Hello World

CMMI

Wed, 09 Mar 2011 10:59:31 +1100

CMMI#

The Capability Maturity Model Integration (CMMI) is a process and behavioral model that helps organizations streamline process improvement and encourage productive, efficient behaviors that decrease risks in software, product and service development.

CMMI model#

The CMMI starts with an appraisal process that evaluates three specific areas: process and service development, service establishment and management, and product and service acquisition. It’s designed to help improve performance by providing businesses with everything they need to consistently develop better products and services.

CMMI 2.0

Wed, 09 Mar 2011 10:59:31 +1100

CMMI 2.0#

Guilding Principles#

Focus of delivering business value
Focus on business performance and results
Flexible, scalable architecture
Reduce redundancy
Use of plain language
Increased use of graphics and iconography for understanding and adoption

Key Improvements#

Demonstrate the value and ROI of aclopting CMMI

Performance capabilities built-in at every level of the model will help organizations to:
- Understand performance needs
- Track, measure and achieve
- Establish performance goals those goals
Improve the overall value for CMMI appraisals and lower time, effort and cost of the appraisal process

COBIT 5

Wed, 09 Mar 2011 10:59:31 +1100

COBIT 5#

COBIT (Control Objectives for Information and Related Technologies) is a business framework for the governance and management of Enterprise IT, created by ISACA.

The framework contains the COBIT 5 framework for governing and managing enterprise IT. It defines a set of generic processes for the management of IT, with each process defined together with process inputs and outputs, key process-activities, process objectives, performance measures and an elementary maturity model.

Scrum VS Kanban

Wed, 09 Mar 2011 10:59:31 +1100

Scrum VS Kanban#

Kanban and scrum are frameworks that help teams adhere to agile principles and get stuff done. Both frameworks will help you build better products(and services) with fewer headaches. While the practices differ, the principles are largely the same.

Agile#

Agile is a structured and iterative approach to project management and product development. t recognizes the volatility of product development, and provides a methodology for self-organizing teams to respond to change without going off the rails.

AWS: IAM

Mon, 01 Jan 0001 00:00:00 +0000

IAM#

AWS Identity and Access Management (IAM) enables you to manage access to AWS services and resources securely. Using IAM, you can create and manage AWS users and groups, and use permissions to allow and deny their access to AWS resources.

Root User#

Every account has a root user in AWS. A root user is something that’s created automatically for you whenever you create an AWS account.
Every single AWS account has a root user.
The trouble is that root users have unrestricted access to every service and resource that is in AWS inside of your account.
The permissions of root user can’t be restricted in any way.

Dos and Don’ts#

You should not be accessing the root account on a regular basis, whether that’s daily, weekly, or whatever.
Make sure that you turn on multi-factor authentication on the root account. Multi-factor authentication used to be called two-factor authentication. It really just means that we know the password and we have some sort of a token that we will get a number generated. It’s something that you might even use your smartphone for. But it now means that I have to know the username and password and I have to have this token that’s going to generate a code. We’ll see more about how you’ll do that later.
Make sure that you’ve disabled your root access keys. This isn’t the interactive login for root, it has to do with how we can access the account programmatically.
Make sure that you rotate the credentials. Just because we say don’t log in doesn’t mean set the password and then forget it.
Don’t share the root user credentials. password. And all that the audit logs show is that root logged in and did the job. Kind of dangerous.
Make sure that you create a user that has administrative privileges that’s assigned to you and that you know the password only.

Features & Functions#

Allows user to have very secure access including through the use of multi-factor authentication and federation.
Grant user a lot of granular control over the specific resources.
Grant temporary access to different people.
Simplify the number of logins by using federating identities
Integrate the IAM solution is with all of the different products that AWS offers.

MFA#

MFA stands for multi-factor authentication
Extra layer of security.
Prevent against imposters, somebody who just happened to guess the right password or happened to actually shoulder surf and watch somebody key in their username and password.

IAM User#

It is an entity that you create in AWS. The IAM user represents the person or service who uses the IAM user to interact with AWS. A primary use for IAM users is to give people the ability to sign in to the AWS Management Console for interactive tasks and to make programmatic requests to AWS services using the API or CLI. A user in AWS consists of a name, a password to sign into the AWS Management Console, and up to two access keys that can be used with the API or CLI.

Azure: CAF - 1

Mon, 01 Jan 0001 00:00:00 +0000

Cloud Adoption Framework#

The Microsoft Cloud Adoption Framework for Azure is proven guidance that’s designed to help you create and implement the business and technology strategies necessary for your organization to succeed in the cloud. It provides best practices, documentation, and tools that cloud architects, IT professionals, and business decision makers need to successfully achieve short-term and long-term objectives.

The Cloud Adoption Framework brings together cloud adoption best practices from Microsoft employees, partners, and customers. It provides a set of tools, guidance, and narratives that help shape technology, business, and people strategies for driving desired business outcomes during your cloud adoption effort. Review the guidance for each methodology below, providing you with easy access to the right guidance at the right time.

Azure: CAF - 2

Mon, 01 Jan 0001 00:00:00 +0000

Function#

Cloud adoption functions deliver technical solutions.
Cloud strategy functions align technical change with business needs.
Cloud operations functions support and operate adopted solutions.
Cloud center of excellence (CCoE) functions improve quality, speed, and resiliency of adoption.
Cloud governance functions manage risk.
Cloud platform functions operate and mature the platform.
Cloud automation functions accelerate adoption and innovation.
Cloud security functions manage security risks.

Team#

cloud strategy team#

To be successful, every cloud adoption journey needs to involve some level of strategic planning. This getting started guide is designed to help you establish a dedicated team or virtual team that can build and deliver on a solid cloud strategy.

Azure: CAF - 3

Mon, 01 Jan 0001 00:00:00 +0000

cloud adoption strategy#

Define and document your motivations: Meet with key stakeholders and executives to document the motivations behind cloud adoption.
Document business outcomes: Engage motivated stakeholders and executives to document specific business outcomes.
Develop a business case: Develop a business case to validate the financial model that supports your motivations and outcomes.
Choose the right first project: Your first cloud adoption project will help align motivations with technical effort. This article can help you choose your first project wisely.

Azure: RBAC - 1

Mon, 01 Jan 0001 00:00:00 +0000

RBAC#

Azure RBAC is an authorization system built on Azure Resource Manager that provides fine-grained access management of Azure resources.

What to do with RBAC#

Allow one user to manage virtual machines in a subscription and another user to manage virtual networks
Allow a DBA group to manage SQL databases in a subscription
Allow a user to manage all resources in a resource group, such as virtual machines, websites, and subnets
Allow an application to access all resources in a resource group

How it works#

The way you control access to resources using Azure RBAC is to create role assignments. This is a key concept to understand – it’s how permissions are enforced. A role assignment consists of three elements: security principal, role definition, and scope.

Azure: RBAC - 2

Mon, 01 Jan 0001 00:00:00 +0000

Roles#

Classic subscription administrator roles
Azure roles
Azure Active Directory (Azure AD) roles

History#

When Azure was initially released, access to resources was managed with just three administrator roles: Account Administrator, Service Administrator, and Co-Administrator. Later, Azure role-based access control (Azure RBAC) was added. Azure RBAC is a newer authorization system that provides fine-grained access management to Azure resources. Azure RBAC includes many built-in roles, can be assigned at different scopes, and allows you to create your own custom roles. To manage resources in Azure AD, such as users, groups, and domains, there are several Azure AD roles. To manage resources in Azure AD, such as users, groups, and domains, there are several Azure AD roles.

Azure: RBAC - 3

Mon, 01 Jan 0001 00:00:00 +0000

Best practices#

Only grant the access users need#

Scope	Roles

| Reader | Resource-specific | Custom | Contributor | Owner|

Data Types & Ownership

Mon, 01 Jan 0001 00:00:00 +0000

Mutability#

Rust encourages you to favor immutability. It’s important that we get compile-time errors when we attempt to change a value that we previously designated as immutable because this very situation can lead to bugs.

But mutability can be very useful. To make them mutable is simply adding mut in front of the variable name. In addition to allowing this value to change, mut conveys intent to future readers of the code by indicating that other parts of the code will be changing this variable value.

DigitialOcean: Droplet

Mon, 01 Jan 0001 00:00:00 +0000

Droplet#

DigitalOcean Droplets are Linux-based virtual machines (VMs) that run on top of virtualized hardware. Each Droplet you create is a new server you can use, either standalone or as part of a larger, cloud-based infrastructure.

Prerequisite#

Prepare a bank account or credit card
Signup DigitalOcean account and activate it
Create a new prject

OS Options#

Ubuntu
FreeBSD
Fedora
Debian
CentOS

Plans and Pricing#

We offer four different kinds of Droplet plans: one shared CPU plan and three dedicated CPU plans.

F# Overview

Mon, 01 Jan 0001 00:00:00 +0000

F`#`#

F# is an open-source, cross-platform, interoperable programming language for writing succinct, robust and performant code. Your focus remains on your problem domain, rather than the details of programming.

Organizing F# Code#

The following table shows reference articles related to organizing your F# code.

Title	Description
Namespaces	Learn about namespace support in F#. A namespace lets you organize code into areas of related functionality by enabling you to attach a name to a grouping of program elements.
Modules	Learn about modules. An F# module is like a namespace and can also include values and functions. Grouping code in modules helps keep related code together and helps avoid name conflicts in your program.
open Declarations	Learn about how open works. An open declaration specifies a module, namespace, or type whose elements you can reference without using a fully qualified name.
Signatures	Learn about signatures and signature files. A signature file contains information about the public signatures of a set of F# program elements, such as types, namespaces, and modules. It can be used to specify the accessibility of these program elements.
Access Control	Learn about access control in F#. Access control means declaring what clients are able to use certain program elements, such as types, methods, functions, and so on.
XML Documentation	Learn about support for generating documentation files for XML doc comments, also known as triple slash comments. You can produce documentation from code comments in F# as in other .NET languages.

Literals and Strings#

The following table shows reference articles that describe literals and strings in F#.

Getting started

Mon, 01 Jan 0001 00:00:00 +0000

Go Introduction#

Golang’s popularity is skyrocketing. The thriving of Docker and Kubernetes push the Golang to a higher level.

Go is easy to become functional with and appropriate for junior developers to work on. Also, having a language that encourages readability and comprehension is extremely useful. The mixture of duck typing (via interfaces) and convenience features such as “:=” for short variable declarations give Go the feel of a dynamically typed language while retaining the positives of a strongly typed one.

Package & Module

Mon, 01 Jan 0001 00:00:00 +0000

Package & Module#

Packages are modules that contain other modules.
Packages are generally implemented as directories containing a special __init__.py file.
The __init__.py file is executed when the package is imported.
Packages can contain sub packages which themselves are implemented with __init__.py files in directories.
The module objects for packages have a __path__ attribute.

sys.path#

List of directories which Python searches for modules.
```
# list directories
>>>import sys
>>>sys.path
```
Use append to attach the package directory to sys.path

AWS : CLI - 1

Mon, 01 Jan 0001 00:00:00 +0000

AWS CLI#

Amazon Virtual Private Cloud (Amazon VPC) enables you to launch AWS resources into a virtual network that you’ve defined. This virtual network closely resembles a traditional network that you’d operate in your own data center, with the benefits of using the scalable infrastructure of AWS.

CLI installation (Version 1)#

Install Python 3#

Python 2.7 is no longer supported. Please install python3
```
 sudo yum install python3
 pip3 --version
```

Profile Setup#

A named profile is a collection of settings and credentials that you can apply to a AWS CLI command. When you specify a profile to run a command, the settings and credentials are used to run that command.

AWS : CLI - 2

Mon, 01 Jan 0001 00:00:00 +0000

AWS CLI & VPC#

Following is a sample to create a VPC with 2 private subnets, 2 public subnets across 2 avaliable zones and NAT Gateway.

#!/bin/bash
#******************************************************************************
# AWS VPC CLI Script
#******************************************************************************
#
# SYNOPSIS
# Automates the creation of a custom IPv4 VPC, having both a public and a
# private subnet, and a NAT gateway.
#
#==============================================================================
#
# NOTES
# VERSION: 1.0
# AUTHOR: Harry Ho
#
#==============================================================================
# MODIFY THE SETTINGS BELOW
#==============================================================================
#
AWS_REGION="ap-southeast-2"
VPC_NAME="DEV-PG-II"
VPC_CIDR="10.5.0.0/16"
SUBNET_PUBLIC_CIDR="10.5.1.0/24"
SUBNET_PUBLIC_AZ="ap-southeast-2a"
SUBNET_PUBLIC_NAME="$VPC_NAME-PubSub-AZ2a"
SUBNET_PRIVATE_CIDR="10.5.2.0/24"
SUBNET_PRIVATE_AZ="ap-southeast-2b"
SUBNET_PRIVATE_NAME="$VPC_NAME-PrvSub-AZ2b"
IGW_NAME="$VPC_NAME-IGW"
NAT_GW_NAME="$VPC_NAME-NAT-GW"
CHECK_FREQUENCY=5
#
#==============================================================================
# DO NOT MODIFY CODE BELOW
#==============================================================================
#
# Create VPC
echo "Creating VPC in preferred region..."
VPC_ID=$(aws ec2 create-vpc \
 --cidr-block $VPC_CIDR \
 --query 'Vpc.{VpcId:VpcId}' \
 --output text \
 --region $AWS_REGION)
echo " VPC ID '$VPC_ID' CREATED in '$AWS_REGION' region."

# Add Name tag to VPC
aws ec2 create-tags \
 --resources $VPC_ID \
 --tags "Key=Name,Value=$VPC_NAME" \
 --region $AWS_REGION
echo " VPC ID '$VPC_ID' NAMED as '$VPC_NAME'."

# Create Public Subnet
echo "Creating Public Subnet..."
SUBNET_PUBLIC_ID=$(aws ec2 create-subnet \
 --vpc-id $VPC_ID \
 --cidr-block $SUBNET_PUBLIC_CIDR \
 --availability-zone $SUBNET_PUBLIC_AZ \
 --query 'Subnet.{SubnetId:SubnetId}' \
 --output text \
 --region $AWS_REGION)
echo " Subnet ID '$SUBNET_PUBLIC_ID' CREATED in '$SUBNET_PUBLIC_AZ'" \
 "Availability Zone."

# Add Name tag to Public Subnet
aws ec2 create-tags \
 --resources $SUBNET_PUBLIC_ID \
 --tags "Key=Name,Value=$SUBNET_PUBLIC_NAME" \
 --region $AWS_REGION
echo " Subnet ID '$SUBNET_PUBLIC_ID' NAMED as" \
 "'$SUBNET_PUBLIC_NAME'."

# Create Private Subnet
echo "Creating Private Subnet..."
SUBNET_PRIVATE_ID=$(aws ec2 create-subnet \
 --vpc-id $VPC_ID \
 --cidr-block $SUBNET_PRIVATE_CIDR \
 --availability-zone $SUBNET_PRIVATE_AZ \
 --query 'Subnet.{SubnetId:SubnetId}' \
 --output text \
 --region $AWS_REGION)
echo " Subnet ID '$SUBNET_PRIVATE_ID' CREATED in '$SUBNET_PRIVATE_AZ'" \
 "Availability Zone."

# Add Name tag to Private Subnet
aws ec2 create-tags \
 --resources $SUBNET_PRIVATE_ID \
 --tags "Key=Name,Value=$SUBNET_PRIVATE_NAME" \
 --region $AWS_REGION
echo " Subnet ID '$SUBNET_PRIVATE_ID' NAMED as '$SUBNET_PRIVATE_NAME'."

# Create Internet gateway
echo "Creating Internet Gateway..."
IGW_ID=$(aws ec2 create-internet-gateway \
 --query 'InternetGateway.{InternetGatewayId:InternetGatewayId}' \
 --output text \
 --region $AWS_REGION)
echo " Internet Gateway ID '$IGW_ID' CREATED."

# Add Name tag to Internet gateway
aws ec2 create-tags \
 --resources $IGW_ID \
 --tags "Key=Name,Value=$IGW_NAME" \
 --region $AWS_REGION
echo " Internet gateway '$IGW_ID' NAMED as '$IGW_NAME'."


# Attach Internet gateway to your VPC
aws ec2 attach-internet-gateway \
 --vpc-id $VPC_ID \
 --internet-gateway-id $IGW_ID \
 --region $AWS_REGION
echo " Internet Gateway ID '$IGW_ID' ATTACHED to VPC ID '$VPC_ID'."

# Create Route Table
echo "Creating Route Table..."
ROUTE_TABLE_ID=$(aws ec2 create-route-table \
 --vpc-id $VPC_ID \
 --query 'RouteTable.{RouteTableId:RouteTableId}' \
 --output text \
 --region $AWS_REGION)
echo " Route Table ID '$ROUTE_TABLE_ID' CREATED."


# Create route to Internet Gateway
RESULT=$(aws ec2 create-route \
 --route-table-id $ROUTE_TABLE_ID \
 --destination-cidr-block 0.0.0.0/0 \
 --gateway-id $IGW_ID \
 --region $AWS_REGION)
echo " Route to '0.0.0.0/0' via Internet Gateway ID '$IGW_ID' ADDED to" \
 "Route Table ID '$ROUTE_TABLE_ID'."

# Associate Public Subnet with Route Table
RESULT=$(aws ec2 associate-route-table \
 --subnet-id $SUBNET_PUBLIC_ID \
 --route-table-id $ROUTE_TABLE_ID \
 --region $AWS_REGION)
echo " Public Subnet ID '$SUBNET_PUBLIC_ID' ASSOCIATED with Route Table ID" \
 "'$ROUTE_TABLE_ID'."

# Enable Auto-assign Public IP on Public Subnet
aws ec2 modify-subnet-attribute \
 --subnet-id $SUBNET_PUBLIC_ID \
 --map-public-ip-on-launch \
 --region $AWS_REGION
echo " 'Auto-assign Public IP' ENABLED on Public Subnet ID" \
 "'$SUBNET_PUBLIC_ID'."

# Allocate Elastic IP Address for NAT Gateway
echo "Creating NAT Gateway..."
EIP_ALLOC_ID=$(aws ec2 allocate-address \
 --domain vpc \
 --query '{AllocationId:AllocationId}' \
 --output text \
 --region $AWS_REGION)
echo " Elastic IP address ID '$EIP_ALLOC_ID' ALLOCATED."

# Create NAT Gateway
NAT_GW_ID=$(aws ec2 create-nat-gateway \
 --subnet-id $SUBNET_PUBLIC_ID \
 --allocation-id $EIP_ALLOC_ID \
 --query 'NatGateway.{NatGatewayId:NatGatewayId}' \
 --output text \
 --region $AWS_REGION)

FORMATTED_MSG="Creating NAT Gateway ID '$NAT_GW_ID' and waiting for it to "
FORMATTED_MSG+="become available.\n Please BE PATIENT as this can take some "
FORMATTED_MSG+="time to complete.\n ......\n"
printf " $FORMATTED_MSG"
FORMATTED_MSG="STATUS: AVAILABLE - Total of %02d seconds elapsed for process"
FORMATTED_MSG+="\n ......\n NAT Gateway ID '%s' is now AVAILABLE.\n"
start_time="$(date -u +%s)"

aws ec2 wait nat-gateway-available \
 --nat-gateway-ids $NAT_GW_ID

end_time="$(date -u +%s)"
elapsed="$(($end_time-$start_time))" 

printf " $FORMATTED_MSG" $elapsed $NAT_GW_ID

# Add Name tag to NAT Gateway
aws ec2 create-tags \
 --resources $NAT_GW_ID \
 --tags "Key=Name,Value=$NAT_GW_NAME" \
 --region $AWS_REGION
echo " Internet gateway '$NAT_GW_ID' NAMED as '$NAT_GW_NAME'."


# Create route to NAT Gateway
MAIN_ROUTE_TABLE_ID=$(aws ec2 describe-route-tables \
 --filters Name=vpc-id,Values=$VPC_ID Name=association.main,Values=true \
 --query 'RouteTables[*].{RouteTableId:RouteTableId}' \
 --output text \
 --region $AWS_REGION)
echo " Main Route Table ID is '$MAIN_ROUTE_TABLE_ID'."
RESULT=$(aws ec2 create-route \
 --route-table-id $MAIN_ROUTE_TABLE_ID \
 --destination-cidr-block 0.0.0.0/0 \
 --gateway-id $NAT_GW_ID \
 --region $AWS_REGION)
echo " Route to '0.0.0.0/0' via NAT Gateway with ID '$NAT_GW_ID' ADDED to" \
 "Route Table ID '$MAIN_ROUTE_TABLE_ID'."
echo "COMPLETED"

AWS : CLI - 3

Mon, 01 Jan 0001 00:00:00 +0000

AWS CLI & & Security Group#

Sometimes it is so annoying to update the rules of security group one by one, because of the change of your public IP address. Following is a script to make such change easier.

The script will only update the SSH / RDP protocals of specified the security groups. The SSH and RDP are most popular ones which allow admin to access the remote EC2.

Closure & Decorator

Mon, 01 Jan 0001 00:00:00 +0000

Closure & Decorator#

LEGB rules#

Local, Enclosing, Gloable, Built-in

Local function#

Useful for specialized, one-off functions
Aid in code organization and readability
Similar to lambdas, but more general
May contain multiple expressions
May contain statements

Closure#

Closure maintain references to objects from earlier scopes
LEGB does not apply when making new bindings

Usage of nonlocal

Example

def make_timer():
 last_called = None

 def elapsed():
 nonlocal last_called
 now = time.time()
 if last_called is None:
 last_called = now
 return None
 result = now - last_called
 last_called = now
 return result
 return elapsed


if __name__ == "__main__":
 mt = make_timer()
 print(mt ())
 print('-----------------------------')
 print(mt ())
 print('-----------------------------')
 print(mt ())

Use as function factory

DigitialOcean: Get Started

Mon, 01 Jan 0001 00:00:00 +0000

User Setup#

Create a new admin user#

Add a new user#

# Add new user 
# set password
adduser <admin_user>

# user to sudo group
usermod -aG sudo <admin_user>

Set SSH access for new user#

# Switch session to new user 
su - <admin_user>

# navigate to user home 
cd

# Prepare ssh directory
mkdir .ssh
chmod 700 ~/.ssh

# Copy root key
sudo cp /root/.ssh/authorized_keys ~/.ssh/authorized_keys
chmod 644 /home/<admin_user>/.ssh/authorized_keys
sudo chown -R <admin_user>:<admin_user> ~/

ssh -i ~/.ssh/<your_droplet_rsa> <admin_user>@<your_droplet_ip>

Set root password & disable SSH#

sudo passwd

# rename key file
sudo mv /root/.ssh/authorized_keys /root/.ssh/disabled_authorized_keys

Security Update#

# Update only for security
sudo apt-get install unattended-upgrades

# Update security packages
sudo unattended-upgrade -d --dry-run
sudo unattended-upgrade -d

# Update quietly
sudo unattended-upgrade

Tagging & Cloud Firewall#

Tags are custom labels you apply to Droplets that have multiple uses
- Add tags to your droplet. e.g. my-web-server
DigitalOcean Cloud Firewalls are a free, network-based, stateful firewall service for your DigitalOcean Droplets. They block all traffic that isn’t expressly permitted by a rule. You can define the Droplets protected by a firewall individually or by using tags.
Always setup Firewall for your droplets
- Set SSH permission for only given IP address
- Set HTTP for port 80
- Set HTTPS for port 443

Other Features#

Floating IPs#

DigitalOcean Floating IPs are publicly-accessible static IP addresses that you can assign to Droplets. A floating IP provides an additional static address you can use to access a Droplet without replacing or changing the Droplet’s original public IP address.

Map, Function & Closure

Mon, 01 Jan 0001 00:00:00 +0000

Map#

Maps are a special kind of data structure: an unordered collection of pairs of items, where one element of the pair is the key, and the other element, associated with the key, is the data or the value, hence they are also called associative arrays or dictionaries.
The key type can be any type for which the operations == and != are defined, like string, int, float. The value type can be any type.

Project, Vector, String & Hashmap

Mon, 01 Jan 0001 00:00:00 +0000

Project management#

Rust has a number of features that allow you to manage your code’s organization, including which details are exposed, which details are private, and what names are in each scope in your programs.
- Packages: A Cargo feature that lets you build, test, and share crates
- Crates: A tree of modules that produces a library or executable
- Modules and use: Let you control the organization, scope, and privacy of paths
- Paths: A way of naming an item, such as a struct, function, or module

Package & Crate#

A package is one or more crates that provide a set of functionality. A package contains a Cargo.toml file that describes how to build those crates.

AWS: VPC - 1

Mon, 01 Jan 0001 00:00:00 +0000

VPC Part 1#

Key concepts#

A virtual private cloud (VPC) is a virtual network dedicated to your AWS account.
A subnet is a range of IP addresses in your VPC.
A route table contains a set of rules, called routes, that are used to determine where network traffic is directed.
An internet gateway is a horizontally scaled, redundant, and highly available VPC component that allows communication between instances in your VPC and the internet. It therefore imposes no availability risks or bandwidth constraints on your network traffic.
A VPC endpoint enables you to privately connect your VPC to supported AWS services and VPC endpoint services powered by PrivateLink without requiring an internet gateway, NAT device, VPN connection, or AWS Direct Connect connection. Instances in your VPC do not require public IP addresses to communicate with resources in the service. Traffic between your VPC and the other service does not leave the Amazon network.

IP addressing#

Once the VPC is created, its CIDR block range can NOT be chagned.
To change CIDR size, you need to create a new VPC
The different subnets within a VPC can NOT be overlap.
Can expand VPC by adding secondary IPv4 CIDR blocks

Default VPC#

AWS creates a default VPC for you in each region. The default VPC will include 1 CIDR block, 1 route table, 1 DHCP options set, 1 Network ACL, 1 Security Group, 1 Internet Gateway, and 3~6 Subnets. The number of subnet depends on the number of Available Zone in the region.

Azure: App - 1

Mon, 01 Jan 0001 00:00:00 +0000

Azure App Service#

Azure App Service is an HTTP-based service for hosting web applications, REST APIs, and mobile back ends. You can develop in your favorite language, be it .NET, .NET Core, Java, Ruby, Node.js, PHP, or Python. Applications run and scale with ease on both Windows and Linux-based environments.

Built-in auto scale support
Continuous integration/deployment support
Deployment slots

Limitations#

App Service on Linux is not supported on Shared pricing tier.
You can’t mix Windows and Linux apps in the same App Service plan.
The Azure portal shows only features that currently work for Linux apps.

Create a Web App#

Create a web app via docker container#

Set defaout subscriptoin

az account set --subscription XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX

Crate a resource group

az group create --name my-ResourceGroup --location <your-region>

Create a service plan

By default, the command below uses an inexpensive B1 pricing tier that is free for the first month. You can control the tier with the –sku parameter.

DigitialOcean: First Web Host

Mon, 01 Jan 0001 00:00:00 +0000

Here I contineu to setup SSL certificates for all sites on my web host

UFW#

UFW, or Uncomplicated Firewall, is a front-end to iptables. Its main goal is to make managing your firewall drop-dead simple and to provide an easy-to-use interface.

DO NOT Enable UFW

DO NOT enable UFW without reading through the instructions

Enable IP V6#

Open the UFW configuration with vi:

sudo vi /etc/default/ufw

Make sure “IPV6” is set to “yes”, like so:

...
IPV6=yes
...

Set default rules#

sudo ufw deny incoming
sudo ufw allow outgoing

Allow SSH / OpenSSH#

Check app list & enable OpenSSH

# List applications
sudo ufw app list

# Allow SSH
sudo ufw allow OpenSSH

Directly allow port 22 or other SSH port, e.g. 2222

sudo ufw allow 22

Enable UFW#

sudo ufw enable
sudo ufw sattus verbose

Nginx#

Install Nginx#

sudo apt install ngix

Set UFW#

# show applications 
sudo ufw app list

# Allow Nginx 
sudo ufw allow 'Nginx Full'
sudo ufw reload

Build Web Host Block#

Create the Directory Structure#

The document root is the directory where the website files for a domain name are stored and served in response to requests. You can set the document root to any location you want.

Error handling

Mon, 01 Jan 0001 00:00:00 +0000

Error#

Rust groups errors into two major categories: recoverable and unrecoverable errors.
Rust doesn’t have exceptions. Instead, it has the type Result<T, E> for recoverable errors and the panic! macro that stops execution when the program encounters an unrecoverable error.

panic! - Unrecoverable Errors#

Rust has the panic! macro. When the panic! macro executes, your program will print a failure message, unwind and clean up the stack, and then quit. This most commonly occurs when a bug of some kind has been detected and it’s not clear to the programmer how to handle the error.

Unwinding the Stack or Aborting in Response#

By default, when a panic occurs, the program starts unwinding, which means Rust walks back up the stack and cleans up the data from each function it encounters. But this walking back and cleanup is a lot of work. The alternative is to immediately abort, which ends the program without cleaning up. Memory that the program was using will then need to be cleaned up by the operating system.

F# Functions

Mon, 01 Jan 0001 00:00:00 +0000

F# Function#

Functions are the fundamental unit of program execution in any programming language. As in other languages, an F# function has a name, can have parameters and take arguments, and has a body. F# also supports functional programming constructs such as treating functions as values, using unnamed functions in expressions, composition of functions to form new functions, curried functions, and the implicit definition of functions by way of the partial application of function arguments.

String & Representation

Mon, 01 Jan 0001 00:00:00 +0000

String & Representation#

str()#

print() -> str() -> __str(self)__
Fallback to repr(). By default, str() simply calls repr()
Produces a readable, human-friendly representation of an object
It is also the string constructor

repr()#

Exactness is more important than human-friendliness
Suited for debugging. Unambiguous, precise, include type
Includes identifying information.
Generally best for logging and developers
The default repr() is not very helpful
As a rule, you should always write a repr() for your classes

Struct & Interface

Mon, 01 Jan 0001 00:00:00 +0000

Struct#

Go supports user-defined or custom types in the form of alias types or structs. A struct tries to represent a real-world entity with its properties. Structs are composite types, to use when you want to define a type which consist of a number of properties, each having their own type and value, grouping pieces of data together.

Struct with tags#

A field in a struct can, apart from a name and a type, also optionally have a tag: this is a string attached to the field, which could be documentation or some other important label. The tag-content cannot be used in normal programming, only the package reflect can access it.

AWS: VPC - 2

Mon, 01 Jan 0001 00:00:00 +0000

VPC Part 2#

VPC has an implicit router (implied router), and you use route tables to control where network traffic is directed.

Route table#

Have up to 200 route tables per VPC
Have up to 50 route entries per route table
Each subnet must be associated with only one route table
The subent (when created) will be associated with main (default) VPC route table
Can change the subnet association to another route table
Can NOT delete the main route table
Every route table in a VPC comes with a default rule that allows all VPC subnets to comminunicate with one another. This rule can NOT be modified or deleted.

Security Group#

It is a virtual firewall
It controls traffic at the EC2ss level
Up to 5 security groups per EC2
Stateful, return traffic, of allowed inbound traffic, is allowed, even if there are no rules to allow it.
Can only have permit rules, can NOT have deny rules
Implicit deny rule at the end
Security group is associated wth EC2’s network interface
Any change on security group takes effect immediately
Default security groupd can not be deleted
It is VPC resource, hence, different EC2 in differenet AZs within the same VPC, can have the same security group applied to them.
It can NOT block a certain range of IP addresses from Internet from gettting to EC2 fleets

Default vs Customized Group#

The default security group has inbound and outbound rules when created. The inboud rule allows all traffics in from the same security group. The outbound rule allows all traffics to any destination. The customized security group has outbound rule only by default.

Azure: CLI - 1

Mon, 01 Jan 0001 00:00:00 +0000

Azure Cli#

The Azure Command-Line Interface (CLI) is a cross-platform command-line tool to connect to Azure and execute administrative commands on Azure resources. It allows the execution of commands through a terminal using interactive command-line prompts or a script.

Install Azure CLI on macOS#

Mac with Intel CPU

brew update && brew install azure-cli

Install Azure Cli with Docker#

Use docker run

docker run -it mcr.microsoft.com/azure-cli

Run with SSH key

docker run -it -v ${HOME}/.ssh:/root/.ssh mcr.microsoft.com/azure-cli

Get Started#

az login

Show accounts

az account list 
az account show

Setup default subscription

az account set --sbuscription XXXX-XXXXX-xXXXX-XXX

Show App Services

az appservice plan list --query-examples

Show Web Apps

az webapp list --query-examples

DigitialOcean: Lets Encrypt

Mon, 01 Jan 0001 00:00:00 +0000

Here I continue to finish the web host setup. The last step of web host setup is to add SSL certificate for each site

Lets Encrypt#

To enable HTTPS on your website, you need to get a certificate (a type of file) from a Certificate Authority (CA). Let’s Encrypt is a CA. In order to get a certificate for your website’s domain from Let’s Encrypt, you have to demonstrate control over the domain. With Let’s Encrypt, you do this using software that uses the ACME protocol, which typically runs on your web host.

F# C.U.R.S.

Mon, 01 Jan 0001 00:00:00 +0000

Class#

Classes are types that represent objects that can have properties, methods, and events.

Syntax#

// Class definition:
type [access-modifier] type-name [type-params] [access-modifier] ( parameter-list ) [ as identifier ] =
[ class ]
[ inherit base-type-name(base-constructor-args) ]
[ let-bindings ]
[ do-bindings ]
member-list
...
[ end ]
// Mutually recursive class definitions:
type [access-modifier] type-name1 ...
and [access-modifier] type-name2 ...
...

Constructors#

The constructor is code that creates an instance of the class type. In an F# class, there is always a primary constructor whose arguments are described in the parameter-list that follows the type name, and whose body consists of the let (and let rec) bindings at the start of the class declaration and the do bindings that follow. The arguments of the primary constructor are in scope throughout the class declaration.

Generic Type & Trait

Mon, 01 Jan 0001 00:00:00 +0000

Generic Type#

Generics are abstract stand-ins for concrete types or other properties. When we’re writing code, we can express the behavior of generics or how they relate to other generics without knowing what will be in their place when compiling and running the code.

Removing Duplication by Extracting a Function#

steps we took to change the duplication code :
- Identify duplicate code.
- Extract the duplicate code into the body of the function and specify the inputs and return values of that code in the function signature.

IO, Json & XML

Mon, 01 Jan 0001 00:00:00 +0000

IO - Read & Write#

Read from user input#

var (
 firstName, lastName, s string
 i int
 f float32
 input = "56.12 / 5212 / Go"
 format = "%f / %d / %s"
)

func main() {
 fmt.Println("Please enter your full name: ")
 fmt.Scanln(&firstName, &lastName)
 // fmt.Scanf("%s %s", &firstName, &lastName)
 fmt.Printf("Hi %s %s!\n", firstName, lastName) // Hi Chris Naegels
 fmt.Sscanf(input, format, &f, &i, &s)
 fmt.Println("From the string we read: ", f, i, s)
 // ouwtput: From the string we read: 56.12 5212 Go
}

Read command-line argument#

func main() {
 who := "Harry "
 if len(os.Args) > 1 {
 who += strings.Join(os.Args[1:], " ")
 }
 fmt.Println("Good Morning", who)
}

Read from file#

Read by lines

func main() {
 inputFile, inputError := os.Open("hello.go")
 if inputError != nil {
 fmt.Printf("An error occurred on opening the inputfile\n" +
 "Does the file exist?\n" +
 "Have you got acces to it?\n")
 return // exit the function on error
 }
 defer inputFile.Close() // Close file before exits the main func
 inputReader := bufio.NewReader(inputFile)
 for {
 inputString, readerError := inputReader.ReadString('\n')
 if readerError == io.EOF {
 return
 }
 fmt.Printf("The input was: %s", inputString)
 }
}

NOTE: The End-of-line characters of text-files in Unix end on \n, but in Windows this is \r\n. By using the method ReadString or ReadBytes with \n as a delimiter you don’t have to worry about this.

Iteration

Mon, 01 Jan 0001 00:00:00 +0000

Iterables & Iteration#

Comprehensions#

Comprehensions can process more than one input sequence
Multiple input sequences in comprehensions work like nested for-loops
Comprehensions can also have multiple if-clauses interspersed with the for-clauses
Later clauses in a comprehension can reference variables bound in earlier clauses
Comprehension can also appear in the result expression of a comprehension, resulting in nested sequences

Example#

## Comprehensions 
>>> points
[(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
>>> points_c=[(x,y) for x in range(3) for y in range(4) ]
>>> points_c
[(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
>>> points_d=[(x,y)
... for x in range(3)
... if x > 0
... for y in range(4)
... if y > x ]
>>> points_d
[(1, 2), (1, 3), (2, 3)]
>>> points_e = [ [ y-1 for y in range(x) ] for x in range(3)]
>>> points_e
[[], [-1], [-1, 0]]

Functional-style tools#

Python provides a number of functional-style tools for working with iterators

Map#

map() calls a function for each element in its input sequences
map() returns an iterable object, not a fully-evaluated collection
map() results are lazily evaluated, meaning that you must access them to force their calculation
map() results are typically evaluated through the use of iteration constructs such as for-loops
You must provide as many input sequences to map() as the callable argument has parameters
map() takes one element from each input sequence for each output element it produces
map() stops producing output when its shortest input sequence is exhausted
map() can be used to implement the same behavior as comprehensions in some cases

Example#

>>> sizes =['small','medium', 'large']
>>> colors = ['lavender', 'teal', 'burnt orange']
>>> animals = ['koala', 'platypus', 'salamander']
>>> def combine( size, color, animal):
... return '{} {} {}'.format(size, color, animal)
...
>>> list(map(combine, sizes, colors, animals ))
['small lavender koala', 'medium teal platypus', 'large burnt orange salamander']
>>> import itertools
>>> def combine2(quantity, size, color, animal):
... return '{} - {} {} {}'.format(quantity, size, color, animal)
...
>>> list(map(combine2, itertools.count(), sizes, colors, animals ))
['0 - small lavender koala', '1 - medium teal platypus', '2 - large burnt orange salamander']

Filter#

filter() selects values from an input sequence which match a specified criteria
filter() passes each element in its input sequence to the function argument
filter() returns an iterable over the input elements for which the function argument is truthy
Like map(), filter() produces its output lazily If you pass None as the first argument to filter(), it yields the input values which evaluate to True in a boolean context reduce() cumulatively applies a function to the elements of an input sequence

Example#

## filter
>>> negs = filter(lambda x: x<0 , [3, -1, 2,-4,0,9,-33])
>>> list(negs)
[-1, -4, -33]
>>> notnones = filter(None, [0,1, False, True, [], () , {}, (1,2,), [1,2], '', 'yes'])
>>> list(map(type, list(notnones)))
[<class 'int'>, <class 'bool'>, <class 'tuple'>, <class 'list'>, <class 'str'>]

Reduce#

reduce() calls the input function with two arguments: the accumulated result so far, and the next element in the sequence
reduce() is a generalization of summation
reduce() returns the accumulated result after all of the input has been processed
If you pass an empty sequence to reduce() it will raise a TypeError
reduce() accepts an optional initial value argument
This initial value is conceptually added to the front of the input sequence
The initial value is returned if the input sequence is empty
The map() and reduce() functions in Python are related to the ideas in the map-reduce algorithm

Example#

## reduce
>>> from functools import reduce
>>> import operator
>>> reduce(operator.add, [1,2,3,4,5])
15

### x is interim result , y is the next sequence value
>>> def mul(x, y):
... print(' mul {} {} '.format(x,y))
... return x * y
...
>>> reduce( mul, range(1, 5))
mul 1 2
mul 2 3
mul 6 4
24

The next() function#

Python’s next() function calls __next__() on its argument
Iterators in Python must support the __next__() method
__next__() should return the next item in the sequence, or raise StopIteration if it is exhausted
Python’s iter() function calls __iter__() on its argument
Iterable objects in Python must support the __iter__() method
__iter__() should return an iterator for the iterable object
Objects with a __getitem__() method that accepts consecutive integer indices starting at zero are also iterables
Iterables implemented via __getitem__() must raise IndexError when they are exhausted

Example of Iterator#

class ExampleIterator:
def __init__(self, data):
 self.index = 0
 self.data = data

def __iter__(self):
 return self

def __next__(self):
 if self.index >= len(self.data):
 raise StopIteration()

 rslt = self.data[self.index]
 self.index += 1
 return rslt

Example of Iterable#

class ExampleIterable:
 def __init__(self):
 self.data = [1, 2, 3]

 def __iter__(self):
 return ExampleIterator(self.data)

Example of AnotherIterable#

class AnotherIterable:
 def __init__(self):
 self.data = [1, 2, 3]

 def __getitem__(self, idx):
 return self.data[idx]

The iter() function#

The extended form of iter() accepts a zero-argument callable and a sentinel value
Extended iter() repeatedly calls the callable argument until it returns the sentinel value
The values produced by extended iter() are those returned from the callable

Example#

>>> ts = iter(datetime.datetime.now, None)
>>> next(ts)
datetime.datetime(2017, 7, 14, 14, 38, 10, 752761)
>>> next(ts)
datetime.datetime(2017, 7, 14, 14, 38, 13, 373613)
>>> next(ts)
datetime.datetime(2017, 7, 14, 14, 38, 14, 754588)

## Read file 
## Content of the file file.txt
## You are reading 
## the file
## you won't read 
## the 
## END
## but not see the END above

>>> with open('file.txt', 'rt') as f:
... for line in iter(lambda: f.readline().strip(), 'END'):
... print(line)
...
You are reading
the file
you won't read
the

One use case for extended iter() is to iterate using simple functions
Protocol conforming iterators must also be iterable

Example of Sensor#

import datetime
import itertools
import random
import time

class Sensor:
 def __iter__(self):
 return self

 def __next__(self):
 return random.random()

sensor = Sensor()
timestamps = iter(datetime.datetime.now, None)

for stamp, value in itertools.islice(zip(timestamps, sensor), 10):
 print(stamp, value)
 time.sleep(1)

AWS: VPC - 3

Mon, 01 Jan 0001 00:00:00 +0000

VPC Part 3#

Endpoint#

A VPC endpoint enables you to privately connect your VPC to supported AWS services and VPC endpoint services powered by AWS PrivateLink without requiring an internet gateway, NAT device, VPN connection, or AWS Direct Connect connection.

Endpoints are virtual devices. They are horizontally scaled, redundant, and highly available VPC components. They allow communication between instances in your VPC and services without imposing availability risks or bandwidth constraints on your network traffic.

Error handling

Mon, 01 Jan 0001 00:00:00 +0000

Error handling#

Go does not have an exception mechanism, like the try/catch in Java or .NET for instance: you cannot throw exceptions. Instead it has a defer-panic-and-recover mechanism.
The Go way to handle errors is for functions and methods to return an error object as their only or last return value—or nil if no error occurred—and for calling functions to always check the error they receive.
Handle the errors and return from the function in which the error occurred with an error message to the user: that way if something does go wrong, your program will continue to function and the user will be notified. The purpose of panic-and-recover is to deal with genuinely exceptional (so unexpected) problems and not with normal errors.

F# Collections 1

Mon, 01 Jan 0001 00:00:00 +0000

Array#

Arrays are fixed-size, zero-based, mutable collections of consecutive data elements that are all of the same type.

Create array#

// 
let array1 = [| 1; 2; 3 |]

// Put each element on a separate line, in which case the semicolon separator is optional.
let array1 =
 [|
 1
 2
 3
 |]

// The type of the array elements is inferred from the literals used and must be consistent. 
// The following code causes an error because 1.0 is a float and 2 and 3 are integers.
// Causes an error.
// let array2 = [| 1.0; 2; 3 |]


// Use sequence expressions to create arrays.
let array3 = [| for i in 1 .. 10 -> i * i |]

// use Array.zeroCreate
let arrayOfTenZeroes : int array = Array.zeroCreate 10

// use Array.empty
let myEmptyArray = Array.empty
printfn "Length of empty array: %d" myEmptyArray.Length
// Length of empty array: 0

// use Array.create
printfn "Array of floats set to 5.0: %A" (Array.create 10 5.0)
// Area of floats set to 5.0: [|5.0; 5.0; 5.0; 5.0; 5.0; 5.0; 5.0; 5.0; 5.0; 5.0|]

// Array.init
printfn "Array of squares: %A" (Array.init 10 (fun index -> index * index))
// Array of squares: [|0; 1; 4; 9; 16; 25; 36; 49; 64; 81|]

Copy#

open System.Text

let firstArray : StringBuilder array = Array.init 3 (fun index -> new StringBuilder(""))
let secondArray = Array.copy firstArray
// Reset an element of the first array to a new value.
firstArray[0] <- new StringBuilder("Test1")
// Change an element of the first array.
firstArray[1].Insert(0, "Test2") |> ignore
printfn "%A" firstArray
printfn "%A" secondArray
// output
// [|Test1; Test2; |]
// [|; Test2; |]

Access#

// Accesses elements from 0 to 2.
array1[0..2]

// Accesses elements from the beginning of the array to 2.
array1[..2]

// Accesses elements from 2 to the end of the array.
array1[2..]

Functions#

// Array.sub 
let a1 = [| 0 .. 99 |]
let a2 = Array.sub a1 5 10
printfn "%A" a2
// output
// [|5; 6; 7; 8; 9; 10; 11; 12; 13; 14|]


// Array.append creates a new array by combining two existing arrays.
printfn "%A" (Array.append [| 1; 2; 3|] [| 4; 5; 6|])
// output
// [|1; 2; 3; 4; 5; 6|]




// Array.choose selects elements of an array to include in a new array. 
printfn "%A" (Array.choose (fun elem -> if elem % 2 = 0 then
 Some(float (elem*elem - 1))
 else
 None) [| 1 .. 10 |])
// output
// [|3.0; 15.0; 35.0; 63.0; 99.0|]


// Array.collect runs a specified function on each array element of an existing array and then collects the elements generated by the function and combines them into a new array. 
printfn "%A" (Array.collect (fun elem -> [| 0 .. elem |]) [| 1; 5; 10|])
// output
// [|0; 1; 0; 1; 2; 3; 4; 5; 0; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10|]


Array.concat takes a sequence of arrays and combines them into a single array. The following code demonstrates Array.concat.

F#

Copy
Array.concat [ [|0..3|] ; [|4|] ]
//output [|0; 1; 2; 3; 4|]

Array.concat [| [|0..3|] ; [|4|] |]
//output [|0; 1; 2; 3; 4|]



// Array.filter takes a Boolean condition function and generates a new array that contains only those elements from the input array for which the condition is true.
printfn "%A" (Array.filter (fun elem -> elem % 2 = 0) [| 1 .. 10|])
// The output
// [|2; 4; 6; 8; 10|]


// Array.rev generates a new array by reversing the order of an existing array. 
let stringReverse (s: string) =
 System.String(Array.rev (s.ToCharArray()))

printfn "%A" (stringReverse("!dlrow olleH"))
// The output 
// "Hello world!"

// You can easily combine functions in the array module that transform arrays by using the pipeline operator (|>)
[| 1 .. 10 |]
|> Array.filter (fun elem -> elem % 2 = 0)
|> Array.choose (fun elem -> if (elem <> 8) then Some(elem*elem) else None)
|> Array.rev
|> printfn "%A"
// output
// [|100; 36; 16; 4|]

Multidimensional arrays#

let my2DArray = array2D [ [ 1; 0]; [0; 1] ]
let arrayOfArrays = [| [| 1.0; 0.0 |]; [|0.0; 1.0 |] |]
let twoDimensionalArray = Array2D.init 2 2 (fun i j -> arrayOfArrays[i][j])

Slicing#

// Get rows 1 to N from an NxM matrix (returns a matrix):
matrix[1.., *]

// Get rows 1 to 3 from a matrix (returns a matrix):
matrix[1..3, *]

// Get columns 1 to 3 from a matrix (returns a matrix):
matrix[*, 1..3]

// Get a 3x3 submatrix:
matrix[1..3, 1..3]

// Get row 3 from a matrix as a vector:
matrix[3, *]

// Get column 3 from a matrix as a vector:
matrix[*, 3]

Matrix & slicing#


type Matrix<'T>(N: int, M: int) =
 let internalArray = Array2D.zeroCreate<'T> N M

 member this.Item
 with get(a: int, b: int) = internalArray[a, b]
 and set(a: int, b: int) (value:'T) = internalArray[a, b] <- value

 member this.GetSlice(rowStart: int option, rowFinish : int option, colStart: int option, colFinish : int option) =
 let rowStart =
 match rowStart with
 | Some(v) -> v
 | None -> 0
 let rowFinish =
 match rowFinish with
 | Some(v) -> v
 | None -> internalArray.GetLength(0) - 1
 let colStart =
 match colStart with
 | Some(v) -> v
 | None -> 0
 let colFinish =
 match colFinish with
 | Some(v) -> v
 | None -> internalArray.GetLength(1) - 1
 internalArray[rowStart..rowFinish, colStart..colFinish]

 member this.GetSlice(row: int, colStart: int option, colFinish: int option) =
 let colStart =
 match colStart with
 | Some(v) -> v
 | None -> 0
 let colFinish =
 match colFinish with
 | Some(v) -> v
 | None -> internalArray.GetLength(1) - 1
 internalArray[row, colStart..colFinish]

 member this.GetSlice(rowStart: int option, rowFinish: int option, col: int) =
 let rowStart =
 match rowStart with
 | Some(v) -> v
 | None -> 0
 let rowFinish =
 match rowFinish with
 | Some(v) -> v
 | None -> internalArray.GetLength(0) - 1
 internalArray[rowStart..rowFinish, col]

module test =
 let generateTestMatrix x y =
 let matrix = new Matrix<float>(3, 3)
 for i in 0..2 do
 for j in 0..2 do
 matrix[i, j] <- float(i) * x - float(j) * y
 matrix

 let test1 = generateTestMatrix 2.3 1.1
 let submatrix = test1[0..1, 0..1]
 printfn $"{submatrix}"

 let firstRow = test1[0,*]
 let secondRow = test1[1,*]
 let firstCol = test1[*,0]
 printfn $"{firstCol}"

Search#


// Array.find takes a Boolean function and returns the first element for which 
// the function returns true, or raises a 
// System.Collections.Generic.KeyNotFoundException if no element that satisfies
// the conditionis found. 
// Array.findIndex is like Array.find, except that it returns the index of 
// the element instead of the element itself.

// The following code uses Array.find and Array.findIndex to locate a number that 
// is both a perfect square and perfect cube.

let arrayA = [| 2 .. 100 |]
let delta = 1.0e-10
let isPerfectSquare (x:int) =
 let y = sqrt (float x)
 abs(y - round y) < delta
let isPerfectCube (x:int) =
 let y = System.Math.Pow(float x, 1.0/3.0)
 abs(y - round y) < delta
let element = Array.find (fun elem -> isPerfectSquare elem && isPerfectCube elem) arrayA
let index = Array.findIndex (fun elem -> isPerfectSquare elem && isPerfectCube elem) arrayA
printfn "The first element that is both a square and a cube is %d and its index is %d." element index
// The output is as follows.
// The first element that is both a square and a cube is 64 and its index is 62.

// ----------------------------------------------------------------------------
// Array.tryFind is like Array.find, except that its result is an option type, 
// and it returns None if no element is found. Array.tryFind should be used 
// instead of Array.find when you do not know whether a matching element is 
// in the array. Similarly, Array.tryFindIndex is like Array.findIndex except 
// that the option type is the return value. If no element is found, the option is None.

let delta = 1.0e-10
let isPerfectSquare (x:int) =
 let y = sqrt (float x)
 abs(y - round y) < delta
let isPerfectCube (x:int) =
 let y = System.Math.Pow(float x, 1.0/3.0)
 abs(y - round y) < delta
let lookForCubeAndSquare array1 =
 let result = Array.tryFind (fun elem -> isPerfectSquare elem && isPerfectCube elem) array1
 match result with
 | Some x -> printfn "Found an element: %d" x
 | None -> printfn "Failed to find a matching element."

lookForCubeAndSquare [| 1 .. 10 |]
lookForCubeAndSquare [| 100 .. 1000 |]
lookForCubeAndSquare [| 2 .. 50 |]
// The output is as follows.
// Found an element: 1
// Found an element: 729
// Failed to find a matching element.


// ----------------------------------------------------------------------------
// Use Array.tryPick when you need to transform an element in addition to finding it. 
// The result is the first element for which the function returns the transformed 
// element as an option value, or None if no such element is found.
// The following code shows the use of Array.tryPick. In this case, instead of
// a lambda expression, several local helper functions are defined to simplify the code.

let findPerfectSquareAndCube array1 =
 let delta = 1.0e-10
 let isPerfectSquare (x:int) =
 let y = sqrt (float x)
 abs(y - round y) < delta
 let isPerfectCube (x:int) =
 let y = System.Math.Pow(float x, 1.0/3.0)
 abs(y - round y) < delta
 // intFunction : (float -> float) -> int -> int
 // Allows the use of a floating point function with integers.
 let intFunction function1 number = int (round (function1 (float number)))
 let cubeRoot x = System.Math.Pow(x, 1.0/3.0)
 // testElement: int -> (int * int * int) option
 // Test an element to see whether it is a perfect square and a perfect
 // cube, and, if so, return the element, square root, and cube root
 // as an option value. Otherwise, return None.
 let testElement elem =
 if isPerfectSquare elem && isPerfectCube elem then
 Some(elem, intFunction sqrt elem, intFunction cubeRoot elem)
 else None
 match Array.tryPick testElement array1 with
 | Some (n, sqrt, cuberoot) -> printfn "Found an element %d with square root %d and cube root %d." n sqrt cuberoot
 | None -> printfn "Did not find an element that is both a perfect square and a perfect cube."

findPerfectSquareAndCube [| 1 .. 10 |]
findPerfectSquareAndCube [| 2 .. 100 |]
findPerfectSquareAndCube [| 100 .. 1000 |]
findPerfectSquareAndCube [| 1000 .. 10000 |]
findPerfectSquareAndCube [| 2 .. 50 |]
// The output is as follows.
// Found an element 1 with square root 1 and cube root 1.
// Found an element 64 with square root 8 and cube root 4.
// Found an element 729 with square root 27 and cube root 9.
// Found an element 4096 with square root 64 and cube root 16.
// Did not find an element that is both a perfect square and a perfect cube.

Modify arrays#

Array.set sets an element to a specified value. Array.fill sets a range of elements in an array to a specified value. The following code provides an example of Array.fill.

F# Collections 2

Mon, 01 Jan 0001 00:00:00 +0000

List#

A list in F# is an ordered, immutable series of elements of the same type. To perform basic operations on lists, use the functions in the List module.

Creating & appending#

Creating and Initializing Lists

// --- creating ---
let list123 = [ 1; 2; 3 ]

// You can also put line breaks between elements, in which case the semicolons are optional. 
let list123 = [
 1
 2
 3 ]


// Normally, all list elements must be the same type. 
// An exception is that a list in which the elements are specified to be a base type
// can have elements that are derived types. Thus the following is acceptable, 
// because both Button and CheckBox derive from Control.
let myControlList : Control list = [ new Button(); new CheckBox() ]

// using a range indicated by integers separated by the range operator (..)
let list1 = [ 1 .. 10 ]


// An empty list.
let listEmpty = []

// use a sequence expression to create a list.
let listOfSquares = [ for i in 1 .. 10 -> i*i ]

// ---- appending -------
// You can attach elements to a list by using the :: (cons) operator. 
// If list1 is [2; 3; 4], the following code creates list2 as [100; 2; 3; 4].
let list2 = 100 :: list1

// You can concatenate lists that have compatible types by using the @ operator, as in the following code. 
// If list1 is [2; 3; 4] and list2 is [100; 2; 3; 4], this code creates list3 as [2; 3; 4; 100; 2; 3; 4].
let list3 = list1 @ list2

Properties#

The list type supports the following properties:

Inheritance & Polymorphism

Mon, 01 Jan 0001 00:00:00 +0000

Inheritance & Polymorphism#

Specify single inheritance by putting a base class in parentheses after defining a class’s name
Subclasses have all of the methods of their base class
It’s often best to explicitly call a base class initializer from a subclass’s initializer
If a class with a single base class doesn’t define an initializer, the base class’s initializer will be called automatically on construction
Python treats __init__() like any other method
Base class __init__() is not called if overridden
Use super() to call base class __init__()
isinstance() takes an object as its first argument and a type as its second
isinstance() determines if its first argument is an instance of the second argument, or any subclass of the second argument
isinstance() can accept a tuple of types as its second argument, in which it returns True if the first argument is of any of those types
Checking for specific types is rare in Python and is sometimes regarded as bad design
isinstance() determines if its first argument is a direct or indirect subclass of, or the same type as, the second argument
Multiple inheritance means having more than one direct base class
You declare multiple base classes with a comma-separated list of class names in parentheses after a class’s name in a class definition
A class can have as many base classes as you want
Python uses a well-defined “method resolution order” to resolve methods at runtime
If a multiply-inheriting class defines no initializer, Python will automatically call the initializer of its first base class on construction
__bases__ is a tuple of types on a class object which defines the base classes for the class
__bases__ is in the same order as in the class definition
__bases__ is populated for both single and multiple inheritance
Method resolution order defines the order in which Python will search an inheritance graph for methods
MRO is short for Method Resolution Order
MRO is stored as a tuple of types in the __mro__ attribute of a class
The mro() method on type objects returns the contents of __mro__ as a list
To resolve a method, Python uses the first entry in a class’s MRO which has the requested method
MRO is dependent on base class declaration order
MRO is calculated by Python using the C3 algorithm
MRO honors base-class ordering from class definitions
MRO puts subclasses before base classes
The relative order of classes in an MRO is consistent across all classes
It is possible to specify an inconsistent base class ordering, in which case Python will raise a TypeError when the class definition is reached
super() operates by using the elements in an MRO that come after some specified type
super() returns a proxy object which forwards calls to the correct objects
There are two distinct types of super() proxies, bound and unbound
Unbound super() proxies are primarily used for implementing other Python features
Bound proxies can be bound to either class objects or instances
Calling super() with a base-class and derived-class argument returns a proxy bound to a class
Calling super() with a class and an instance of that class returns a proxy bound to an instance
A super() proxy takes the MRO of its second argument (or the type of its second argument), finds the first argument in that MRO, and uses everything after it in the MRO for method resolution
Since class-bound proxies aren’t bound to an instance, you can’t directly call instance methods that they resolve for you
However, classmethods resolved by class-bound proxies can be called directly
Python will raise a TypeError if the second argument is not a subclass or instance of the first argument
Inappropriate use of super() can violate some design constraints * Calling super() with no arguments inside an instance method produces an instance-bound proxy
Calling super() with no arguments inside a classmethod produces a class-bound proxy
In both cases, the no-argument form of super() is the same as calling super() with the method’s class as the first argument and the method’s first argument as the second
Since super() works on MROs and not just a class’s base classes, class can be designed to cooperate without prior knowledge of one another
The class object is at the core of Python’s object model
object is the ultimate base class for all other classes in Python
If you don’t specify a base class for a class, Python automatically uses object as the base
Because object is in every class’s inheritance graph, it shows up in every MRO.
object provides hooks for Python’s comparison operators
object provides default __repr__() and __str__() implementations
object implements the core attribute lookup and management functionality in Python
Inheritance in Python is best used as a way to share implementation

Explanation with example#

Example code#

The code below demonstrates the weird super() in Python

AWS: VPC - 4

Mon, 01 Jan 0001 00:00:00 +0000

VPC Part 4#

Simples demo#

Diagram of customized VPC - MyDemoVPC with Internet Gatway and VPN connect

graph LR
 InternetGW(Internet Gateway)
 VirtualGW(Virtual Gateway)
 INTER(Internet - Public)
 InternetGW --- INTER
 VirtualGW --- SERVER
 subgraph MyDemoVPC
 EC2_A(EC2 Instannce A)
 EC2_B(EC2 Instannce B)
 EC2_E(EC2 Instannce E)
 EC2_F(EC2 Instannce F)
 EC2_C[(Database Master)]
 EC2_D[(Database Slave)]
 MainRouteTable(10.0.0.0/16)
 PrvSubnet(10.0.2.0/24)
 PubSubnet(10.0.1.0/24)
 VPNSubnet(10.0.3.0/24)
 MainRouteTable --- InternetGW
 MainRouteTable --- NetworkACL
 NetworkACL --- PubSecGrp
 NetworkACL --- PrivSecGrp
 PrivSecGrp --- PrvSubnet
 VPNSubnet --- VirtualGW
 VPNSubnet --- MainRouteTable
 PubSecGrp --- PubSubnet
 subgraph Implied_Router
 MainRouteTable(10.0.0.0/16)
 end 
 subgraph Private_Subnet
 PrvSubnet
 EC2_C
 EC2_D
 end
 subgraph Public_Subnet
 PubSubnet
 EC2_A
 EC2_B
 end
 subgraph VPN_Subnet
 VPNSubnet
 EC2_E
 EC2_F
 end
 end
 InternetGW
 subgraph Internet
 INTER
 end
 subgraph OnPremise
 SERVER
 end

Customized Route tables of Subnet Public_Subnet

Destination	Target
10.0.1.0/16	local
2002:0a00:0100:0:0:0:0:0/56	local
0.0.0.0/0	InternetGW
::0/0	InternetGW

Main Route tables of Subnet Private_Subnet

Destination	Target
10.0.1.0/16	local
2002:0a00:0100:0:0:0:0:0/56	local

Route table of Subnet VPN_Subnet

Destination	Target
10.0.1.0/16	local
2002:0a00:0100:0:0:0:0:0/56	local
0.0.0.0/0	VirtualGW

AWS: VPC - 5

Mon, 01 Jan 0001 00:00:00 +0000

VPC Part 5#

Direct Connect#

AWS Direct Connect is a cloud service solution that makes it easy to establish a dedicated network connection from your premises to AWS. Using AWS Direct Connect, you can establish private connectivity between AWS and your datacenter, office, or colocation environment, which in many cases can reduce your network costs, increase bandwidth throughput, and provide a more consistent network experience than Internet-based connections.

Using industry standard 802.1q VLANs, this dedicated connection can be partitioned into multiple virtual interfaces. This allows you to use the same connection to access public resources such as objects stored in Amazon S3 using public IP address space, and private resources such as Amazon EC2 instances running within an Amazon Virtual Private Cloud (VPC) using private IP space, while maintaining network separation between the public and private environments. Virtual interfaces can be reconfigured at any time to meet your changing needs.

Collection

Mon, 01 Jan 0001 00:00:00 +0000

Collection#

Collection protocols#

To implement a protocol, objects must support certain operations.
Most collections implement container, sized and iterable.
All except dict and set are sequences
Container: membership testing using in and not in
Sized: Determine number of elements with len(s)

Iterable: Can produce an iterator with iter(s), e.g.

 for item in iterable:
 do_something(item) `len(s)`

Sequence:
- Retrieve elements by index, e.g. item = seq[index]
- Find items by value index = seq.index(item)
- Count items num = seq.count(item)
- Produce a reversed sequence r = reversed(seq)
Set: set algebra operations, including method and infix operators . e.g.

Goroutine & Channel - 1

Mon, 01 Jan 0001 00:00:00 +0000

Goroutine#

A goroutine is implemented as a function or method (this can also be an anonymous or lambda function) and called (invoked) with the keyword go. This starts the function running in parallel with the current computation but in the same address space and with its own stack.
Go’s concurrency primitives provide the basis for a good concurrency program design: expressing program structure so as to represent independently executing actions; so Go’s emphasis is not in the 1 st place on parallelism: concurrent programs may or may not be parallel. Parallelism is the ability to make things run quickly by using multiple processors. But it turns out most often that a well designed concurrent program also has excellent performing parallel capabilities.

AWS: S3 - 1

Mon, 01 Jan 0001 00:00:00 +0000

S3 Part 1#

Amazon Simple Storage Service (Amazon S3) is an object storage service that offers industry-leading scalability, data availability, security, and performance.

Storage feature#

Amazon S3 has various features you can use to organize and manage your data in ways that support specific use cases, enable cost efficiencies, enforce security, and meet compliance requirements. Data is stored as objects within resources called “buckets”, and a single object can be up to 5 terabytes in size. Amazon S3 offers a range of storage classes designed for different use cases.

AWS: S3 - 2

Mon, 01 Jan 0001 00:00:00 +0000

S3 Part 2#

Access#

Access status#

The list buckets view shows whether your bucket is publicly accessible. Amazon S3 labels the permissions for a bucket as follows:

Public – Everyone has access to one or more of the following: List objects, Write objects, Read and write permissions.
Objects can be public – The bucket is not public, but anyone with the appropriate permissions can grant public access to objects.
Buckets and objects not public – The bucket and objects do not have any public access.

AWS: S3 - 3

Mon, 01 Jan 0001 00:00:00 +0000

Use Case#

Problem#

Block all traffic to my Amazon Simple Storage Service (Amazon S3) bucket unless the traffic is from specific Amazon Virtual Private Cloud (VPC) endpoints or certain external IP addresses.

Resolution#

Use a bucket policy to specify which VPC endpoints or external IP addresses can access the S3 bucket.

Note: An external IP address is a public IP address that can be from within a VPC or outside of a VPC. For example, an external IP address can be an Amazon Elastic Compute Cloud (Amazon EC2) instance’s Elastic IP address, or the IP address of a VPC’s NAT gateway or proxy server.

AWS: SQS,SNS,SES - 1

Mon, 01 Jan 0001 00:00:00 +0000

SQS#

Amazon Simple Queue Service (SQS) is a fully managed message queuing service that enables you to decouple and scale microservices, distributed systems, and serverless applications. SQS eliminates the complexity and overhead associated with managing and operating message oriented middleware, and empowers developers to focus on differentiating work. Using SQS, you can send, store, and receive messages between software components at any volume, without losing messages or requiring other services to be available. Get started with SQS in minutes using the AWS console, Command Line Interface or SDK of your choice, and three simple commands.

AWS: SQS,SNS,SES - 2

Mon, 01 Jan 0001 00:00:00 +0000

Use Case#

Overview#

graph LR
 Sender_Email("test@test.com")
 Email_Failed
 Email_Delivered
 SNS_Subscriptions --> Email_Failed
 SNS_Subscriptions --> Email_Delivered
 Bounce_Notification --> Email_Failed
 Complaint_Notification --> Email_Failed
 Delivery_Notification --> Email_Delivered
 subgraph SQS 
 subgraph Email_Status_Queue
 SNS_Subscriptions
 end
 end 
 subgraph SNS
 subgraph Topics
 Email_Failed
 Email_Delivered
 end
 end
 subgraph SES
 Sender_Email
 subgraph Notifications
 Bounce_Notification 
 Complaint_Notification 
 Delivery_Notification 
 end
 end

Create a topic for failed email, e.g. bounce or spam complaint
- It is named Email_Failed in the diagram above
Create a topic for delivered email

Exception & Assertion

Mon, 01 Jan 0001 00:00:00 +0000

Exception & Assertion#

Avoid bad practices in Python exception handling.
Always specify an exception type with except, but don’t be too general.
Don’t Use Assertions for checking arguments

EXamples

lookup exception

def lookups():
 s = [1, 4, 6]
 try:
 item = s[5]
 except LookupError:
 print("Handled IndexError")

 d = dict(a=65, b=66, c=67)
 try:
 value = d['x']
 except LookupError:
 print("Handled KeyError")

if __name__ == '__main__':
 lookups()

## test result 
## Handled IndexError
## Handled KeyError

unicode exception

F# Collections 3

Mon, 01 Jan 0001 00:00:00 +0000

Seq#

A sequence is a logical series of elements all of one type. Sequences are particularly useful when you have a large, ordered collection of data but do not necessarily expect to use all of the elements. Individual sequence elements are computed only as required, so a sequence can provide better performance than a list in situations in which not all the elements are used.

// Sequence that has an increment.
seq { 0 .. 10 .. 100 }

// uses the -> operator, which allows you to specify an expression 
// whose value will become a part of the sequence. 
seq { for i in 1 .. 10 -> i * i }


// specify the do keyword, with an optional yield that follows:
seq { for i in 1 .. 10 do yield i * i }

// The 'yield' is implicit and doesn't need to be specified in most cases.
seq { for i in 1 .. 10 do i * i }

// The following code generates a list of coordinate pairs along with 
// an index into an array that represents the grid. 
// Note that the first for expression requires a do to be specified.
let (height, width) = (10, 10)
let sequence = seq {
 for row in 0 .. width - 1 do
 for col in 0 .. height - 1 ->
 (row, col, row*width + col)
 }

for e in sequence do
 printfn "%A" e

// (0, 0, 0)
// (0, 1, 1)
// (0, 2, 2)
// ...
// (0, 9, 9)
// (1, 0, 10)
// (1, 1, 11)
// (1, 2, 12)
// ...
// (9, 9, 99)

yield! keyword#

// Repeats '1 2 3 4 5' ten times
seq {
 for _ in 1..10 do
 yield! seq { 1; 2; 3; 4; 5}
}

// When yield! is used in an expression, all other single values 
// must use the yield keyword:
// Combine repeated values with their values
seq {
 for x in 1..10 do
 yield x
 yield! seq { for i in 1..x -> i}
}


// Prime number
// Recursive isprime function.
let isprime n =
 let rec check i =
 i > n/2 || (n % i <> 0 && check (i + 1))
 check 2

let aSequence =
 seq {
 for n in 1..100 do
 if isprime n then
 n
 }

for x in aSequence do
 printfn "%d" x
// output
// 1 2 3 5 7 ...47 53 ... 89 97


// Following example creates a multiplication table that consists of 
// tuples of three elements, each consisting of two factors and the product
let multiplicationTable =
 seq {
 for i in 1..9 do
 for j in 1..9 ->
 (i, j, i*j)
 }



// Yield the values of a binary tree in a sequence.
type Tree<'a> =
 | Tree of 'a * Tree<'a> * Tree<'a>
 | Leaf of 'a

// inorder : Tree<'a> -> seq<'a>
let rec inorder tree =
 seq {
 match tree with
 | Tree(x, left, right) ->
 yield! inorder left
 yield x
 yield! inorder right
 | Leaf x -> yield x
 }

let mytree = Tree(6, Tree(2, Leaf(1), Leaf(3)), Leaf(9))
let seq1 = inorder mytree
printfn "%A" seq1
// outut 
// seq [1; 2; 3; 6; ...]

Functions#


// Using Seq.empty, or you can create a sequence of just one 
// specified element by using Seq.singleton.
let seqEmpty = Seq.empty
let seqOne = Seq.singleton 10
printfn "%A" seqOne
// output: seq [10]

// use Seq.init to create a sequence for which the elements are created 
// by using a function that you provide. You also provide a size for 
// the sequence. This function is just like List.init, except that the 
// elements are not created until you iterate through the sequence.
let seqFirst5MultiplesOf10 = Seq.init 5 (fun n -> n * 10)
Seq.iter (fun elem -> printf "%d " elem) seqFirst5MultiplesOf10
// The output is
// 0 10 20 30 40

// Convert an array to a sequence by using a cast.
let seqFromArray1 = [| 1 .. 10 |] :> seq<int>

// Convert an array to a sequence by using Seq.ofArray.
let seqFromArray2 = [| 1 .. 10 |] |> Seq.ofArray

// using Seq.cast, you can create a sequence from a weakly typed 
// collection, such as those defined in System.Collections. 
open System

let arr = ResizeArray<int>(10)

for i in 1 .. 10 do
 arr.Add(10)

let seqCast = Seq.cast arr


// Seq.unfold generates a sequence from a computation function that takes 
// a state and transforms it to produce each subsequent element in the sequence
let seq1 =
 0 // Initial state
 |> Seq.unfold (fun state ->
 if (state > 20) then
 None
 else
 Some(state, state + 1))

printfn "The sequence seq1 contains numbers from 0 to 20."

for x in seq1 do
 printf "%d " x
// output
// The sequence seq1 contains numbers from 0 to 20.
// 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

let fib =
 (1, 1) // Initial state
 |> Seq.unfold (fun state ->
 if (snd state > 1000) then
 None
 else
 Some(fst state + snd state, (snd state, fst state + snd state)))

printfn "\nThe sequence fib contains Fibonacci numbers."
for x in fib do printf "%d " x
// output
// The sequence fib contains Fibonacci numbers.
// 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597

Example#

// generateInfiniteSequence generates sequences of floating point
// numbers. The sequences generated are computed from the fDenominator
// function, which has the type (int -> float) and computes the
// denominator of each term in the sequence from the index of that
// term. The isAlternating parameter is true if the sequence has
// alternating signs.
let generateInfiniteSequence fDenominator isAlternating =
 if (isAlternating) then
 Seq.initInfinite (fun index ->
 1.0 /(fDenominator index) * (if (index % 2 = 0) then -1.0 else 1.0))
 else
 Seq.initInfinite (fun index -> 1.0 /(fDenominator index))

// The harmonic alternating series is like the harmonic series
// except that it has alternating signs.
let harmonicAlternatingSeries = generateInfiniteSequence (fun index -> float index) true

// This is the series of reciprocals of the odd numbers.
let oddNumberSeries = generateInfiniteSequence (fun index -> float (2 * index - 1)) true

// This is the series of recipocals of the squares.
let squaresSeries = generateInfiniteSequence (fun index -> float (index * index)) false

// This function sums a sequence, up to the specified number of terms.
let sumSeq length sequence =
 (0, 0.0)
 |>
 Seq.unfold (fun state ->
 let subtotal = snd state + Seq.item (fst state + 1) sequence
 if (fst state >= length) then
 None
 else
 Some(subtotal, (fst state + 1, subtotal)))

// This function sums an infinite sequence up to a given value
// for the difference (epsilon) between subsequent terms,
// up to a maximum number of terms, whichever is reached first.
let infiniteSum infiniteSeq epsilon maxIteration =
 infiniteSeq
 |> sumSeq maxIteration
 |> Seq.pairwise
 |> Seq.takeWhile (fun elem -> abs (snd elem - fst elem) > epsilon)
 |> List.ofSeq
 |> List.rev
 |> List.head
 |> snd

// Compute the sums for three sequences that converge, and compare
// the sums to the expected theoretical values.
let result1 = infiniteSum harmonicAlternatingSeries 0.00001 100000
printfn "Result: %f ln2: %f" result1 (log 2.0)
// output
// Result: 0.693152 ln2: 0.693147

let pi = Math.PI
let result2 = infiniteSum oddNumberSeries 0.00001 10000
printfn "Result: %f pi/4: %f" result2 (pi/4.0)
// output
// Result: 0.785373 pi/4: 0.785398

// Because this is not an alternating series, a much smaller epsilon
// value and more terms are needed to obtain an accurate result.
let result3 = infiniteSum squaresSeries 0.0000001 1000000
printfn "Result: %f pi*pi/6: %f" result3 (pi*pi/6.0)
// output
// Result: 1.644618 pi*pi/6: 1.644934

Transforming#

// Seq.pairwise creates a new sequence in which successive elements of the input
// sequence are grouped into tuples.
let printSeq seq1 = Seq.iter (printf "%A ") seq1; printfn ""
let seqPairwise = Seq.pairwise (seq { for i in 1 .. 10 -> i*i })
printSeq seqPairwise
// output
// (1, 4) (4, 9) (9, 16) (16, 25) (25, 36) (36, 49) (49, 64) (64, 81) (81, 100) 


printfn ""
let seqDelta = Seq.map (fun elem -> snd elem - fst elem) seqPairwise
printSeq seqDelta
// output
// 3 5 7 9 11 13 15 17 19 



// Seq.windowed is like Seq.pairwise, except that instead of producing a 
// sequence of tuples, it produces a sequence of arrays that contain copies 
// of adjacent elements (a window) from the sequence. You specify the number 
// of adjacent elements you want in each array.

let seqNumbers = [ 1.0; 1.5; 2.0; 1.5; 1.0; 1.5 ] :> seq<float>
let seqWindows = Seq.windowed 3 seqNumbers
let seqMovingAverage = Seq.map Array.average seqWindows
printfn "Initial sequence: "
printSeq seqNumbers
// 1.0 1.5 2.0 1.5 1.0 1.5 
printfn "\nWindows of length 3: "
printSeq seqWindows
// [|1.0; 1.5; 2.0|] [|1.5; 2.0; 1.5|] [|2.0; 1.5; 1.0|] [|1.5; 1.0; 1.5|] 

printfn "\nMoving average: "
printSeq seqMovingAverage
// 1.5 1.666666667 1.5 1.333333333

Sorting, Comparing & Grouping#

// Seq.compareWith function. The function compares successive elements in 
// turn, and stops when it encounters the first unequal pair. Any additional 
// elements do not contribute to the comparison.
let sequence1 = seq { 1 .. 10 }
let sequence2 = seq { 10 .. -1 .. 1 }

// Compare two sequences element by element.
let compareSequences =
 Seq.compareWith (fun elem1 elem2 ->
 if elem1 > elem2 then 1
 elif elem1 < elem2 then -1
 else 0)

let compareResult1 = compareSequences sequence1 sequence2
match compareResult1 with
| 1 -> printfn "Sequence1 is greater than sequence2."
| -1 -> printfn "Sequence1 is less than sequence2."
| 0 -> printfn "Sequence1 is equal to sequence2."
| _ -> failwith("Invalid comparison result.")
// val compareResult1: int = -1


// Seq.countBy takes a function that generates a value called a key for 
// each element. A key is generated for each element by calling this function 
// on each element. Seq.countBy then returns a sequence that contains the key 
// values, and a count of the number of elements that generated each value of 
// the key.

let mySeq1 = seq { 1.. 100 }

let printSeq seq1 = Seq.iter (printf "%A ") seq1

let seqResult =
 mySeq1
 |> Seq.countBy (fun elem ->
 if elem % 3 = 0 then 0
 elif elem % 3 = 1 then 1
 else 2)

printSeq seqResult
// (1, 34) (2, 33) (0, 33)



// Seq.groupBy takes a sequence and a function that generates a key from an 
// element. The function is executed on each element of the sequence. 
// Seq.groupBy returns a sequence of tuples, where the first element of each 
// tuple is the key and the second is a sequence of elements that produce 
// that key.

let sequence = seq { 1 .. 100 }

let printSeq seq1 = Seq.iter (printf "%A ") seq1

let sequences3 =
 sequences
 |> Seq.groupBy (fun index ->
 if (index % 3 = 0) then 0
 elif (index % 3 = 1) then 1
 else 2)

sequences3 |> printSeq
// (1, seq [1; 4; 7; 10; ...]) (2, seq [2; 5; 8; 11; ...]) (0, seq [3; 6; 9; 12; ...])




// Seq.distinct. Or Seq.distinctBy, which takes a key-generating function to 
// be called on each element. The resulting sequence contains elements of the 
// original sequence that have unique keys; later elements that produce a 
// duplicate key to an earlier element are discarded.
let binary n =
 let rec generateBinary n =
 if (n / 2 = 0) then [n]
 else (n % 2) :: generateBinary (n / 2)

 generateBinary n
 |> List.rev
 |> Seq.ofList

printfn "%A" (binary 1024)
// [1; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0]


let resultSequence = Seq.distinct (binary 1024)
printfn "%A" resultSequence
// seq [1; 0]

let inputSequence = { -5 .. 10 }
let printSeq seq1 = Seq.iter (printf "%A ") seq1

printfn "Original sequence: "
printSeq inputSequence
// -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 

printf ""
printfn "\nSequence with distinct absolute values: "
let seqDistinctAbsoluteValue = Seq.distinctBy (fun elem -> abs elem) inputSequence
printSeq seqDistinctAbsoluteValue
// -5 -4 -3 -2 -1 0 6 7 8 9 10

Slice#

In F#, a slice is a subset of any data type. Slices are similar to indexers, but instead of yielding a single value from the underlying data structure, they yield multiple ones. Slices use the .. operator syntax to select the range of specified indices in a data type.

Goroutine & Channel - 2

Mon, 01 Jan 0001 00:00:00 +0000

Channel directionality#

A channel type may be annotated to specify that it may only send or only receive

 var send_only chan<- int // channel can only receive data
 var recv_only <-chan int // channel can only send data

Receive-only channels ( <-chan T ) cannot be closed, because closing a channel is intended as a way for a sender to signal that no more values will be sent to the channel, so it has no meaning for receive-only channels.

Context

Mon, 01 Jan 0001 00:00:00 +0000

Context managers#

context manager#

context manager an object designed to be used in a with-statement

with context-manager:
 body

with context-manager:
 context-manager.begin()
 body
 context-manager.end()

with context-manager:
 setup()
 body
 teardown()

with context-manager:
 context-manager.begin()
 body
 context-manager.end() 

with context-manager:
 allocation()
 body
 deallocation()

with context-manager:
 enter()
 body
 exit()

A context-manager ensures that resources are properly and automatically managed

F# Pattern Matching

Mon, 01 Jan 0001 00:00:00 +0000

Pattern#

Patterns are rules for transforming input data. They are used throughout F# to compare data with a logical structure or structures, decompose data into constituent parts, or extract information from data in various ways.

Name	Description	Example
Constant pattern	Any numeric, character, or string literal, an enumeration constant, or a defined literal identifier	1.0, “test”, 30, Color.Red
Identifier pattern	A case value of a discriminated union, an exception label, or an active pattern case	Some(x) Failure(msg)
Variable pattern	identifier	a
as pattern	pattern as identifier	(a, b) as tuple1
OR pattern	pattern1	pattern2
AND pattern	pattern1 & pattern2	(a, b) & (_, “test”)
Cons pattern	identifier :: list-identifier	h :: t
List pattern	[ pattern_1; … ; pattern_n ]	[ a; b; c ]
Array pattern	[	pattern_1; ..; pattern_n
Parenthesized pattern	( pattern )	( a )
Tuple pattern	( pattern_1, … , pattern_n )	( a, b )
Record pattern	{ identifier1 = pattern_1; … ; identifier_n = pattern_n }	{ Name = name; }
Wildcard pattern	_	_
Pattern together with type annotation	pattern : type	a : int
Type test pattern	:? type [ as identifier ]	:? System.DateTime as dt
Null pattern	null	null
Nameof pattern	nameof expr	nameof str

Constant Patterns#


[<Literal>]
let Three = 3

let filter123 x =
 match x with
 // The following line contains literal patterns combined with an OR pattern.
 | 1 | 2 | Three -> printfn "Found 1, 2, or 3!"
 // The following line contains a variable pattern.
 | var1 -> printfn "%d" var1

for x in 1..10 do filter123 x
// Found 1, 2, or 3!
// Found 1, 2, or 3!
// Found 1, 2, or 3!
// 4
// 5
// 6
// 7
// 8
// 9
// 10


type Color =
 | Red = 0
 | Green = 1
 | Blue = 2

let printColorName (color:Color) =
 match color with
 | Color.Red -> printfn "Red"
 | Color.Green -> printfn "Green"
 | Color.Blue -> printfn "Blue"
 | _ -> ()

printColorName Color.Red
printColorName Color.Green
printColorName Color.Blue
// Red
// Green
// Blue

Identifier Patterns#

let printOption (data : int option) =
 match data with
 | Some var1 -> printfn "%d" var1
 | None -> ()

type PersonName =
 | FirstOnly of string
 | LastOnly of string
 | FirstLast of string * string

let constructQuery personName =
 match personName with
 | FirstOnly(firstName) -> printfn "May I call you %s?" firstName
 | LastOnly(lastName) -> printfn "Are you Mr. or Ms. %s?" lastName
 | FirstLast(firstName, lastName) -> printfn "Are you %s %s?" firstName lastName

constructQuery (FirstOnly("john"))
constructQuery (LastOnly("smith"))
constructQuery (FirstLast("john","smith"))
// May I call you john?
// Are you Mr. or Ms. smith?
// Are you john smith?

Variable Patterns#

let function1 x =
 match x with
 | (var1, var2) when var1 > var2 -> printfn "%d is greater than %d" var1 var2
 | (var1, var2) when var1 < var2 -> printfn "%d is less than %d" var1 var2
 | (var1, var2) -> printfn "%d equals %d" var1 var2

function1 (1,2)
function1 (2, 1)
function1 (0, 0)
// 1 is less than 2
// 2 is greater than 1
// 0 equals 0

as Pattern#

The as pattern is a pattern that has an as clause appended to it.

Packaging

Mon, 01 Jan 0001 00:00:00 +0000

Package#

Package is a way to structure code: a program is constructed as a “package” (often abbreviated as pkg), which may use facilities from other packages. Every go-file belongs to one (and only one) package (like a library or namespace in other languages). Many different .go files can belong to one package, so the filename(s) and package name are generally not the same.
The package to which the code-file belongs must be indicated on the first line, e.g.: package main . A standalone executable belongs to package main. Each Go application contains one package called main. An application can consist of different packages, but even if you use only package main, you don’t have to stuff all code in 1 big file: you can make a number of smaller files each having package main as 1 st codeline. If you compile a source file with a package name other than main, like pack1, the object file is stored in pack1.a; a package name is written in lowercase letters.

ABC

Mon, 01 Jan 0001 00:00:00 +0000

ABC - Abstract Base Classes#

Abstract base classes complement duck-typing by providing a way to define interfaces when other techniques like hasattr() would be clumsy or subtly wrong (for example with magic methods). ABCs introduce virtual subclasses, which are classes that don’t inherit from a class but are still recognized by isinstance() and issubclass(); see the abc module documentation. Python comes with many built-in ABCs for data structures (in the collections module), numbers (in the numbers module), and streams (in the io module). You can create your own ABCs with the abc module.

F# Active Patterns

Mon, 01 Jan 0001 00:00:00 +0000

Active Patterns#

Active patterns enable you to define named partitions that subdivide input data, so that you can use these names in a pattern matching expression just as you would for a discriminated union. You can use active patterns to decompose data in a customized manner for each partition.

Syntax#

// Active pattern of one choice.
let (|identifier|) [arguments] valueToMatch = expression

// Active Pattern with multiple choices.
// Uses a FSharp.Core.Choice<_,...,_> based on the number of case names. In F#, the limitation n <= 7 applies.
let (|identifier1|identifier2|...|) valueToMatch = expression

// Partial active pattern definition.
// Uses a FSharp.Core.option<_> to represent if the type is satisfied at the call site.
let (|identifier|_|) [arguments] valueToMatch = expression

Examples#

Multiple choices

let (|Even|Odd|) input = if input % 2 = 0 then Even else Odd
let TestNumber input =
 match input with
 | Even -> printfn "%d is even" input
 | Odd -> printfn "%d is odd" input

TestNumber 7
TestNumber 11
TestNumber 32
// output
// 7 is odd
// 11 is odd
// 32 is even

Decompose data types


open System.Drawing

let (|RGB|) (col : System.Drawing.Color) =
 ( col.R, col.G, col.B )

let (|HSB|) (col : System.Drawing.Color) =
 ( col.GetHue(), col.GetSaturation(), col.GetBrightness() )

let printRGB (col: System.Drawing.Color) =
 match col with
 | RGB(r, g, b) -> printfn " Red: %d Green: %d Blue: %d" r g b

let printHSB (col: System.Drawing.Color) =
 match col with
 | HSB(h, s, b) -> printfn " Hue: %f Saturation: %f Brightness: %f" h s b

let printAll col colorString =
 printfn "%s" colorString
 printRGB col
 printHSB col

printAll Color.Red "Red"
printAll Color.Black "Black"
printAll Color.White "White"
printAll Color.Gray "Gray"
printAll Color.BlanchedAlmond "BlanchedAlmond"

// Red
// Red: 255 Green: 0 Blue: 0
// Hue: 360.000000 Saturation: 1.000000 Brightness: 0.500000
// Black
// Red: 0 Green: 0 Blue: 0
// Hue: 0.000000 Saturation: 0.000000 Brightness: 0.000000
// White
// Red: 255 Green: 255 Blue: 255
// Hue: 0.000000 Saturation: 0.000000 Brightness: 1.000000
// Gray
// Red: 128 Green: 128 Blue: 128
// Hue: 0.000000 Saturation: 0.000000 Brightness: 0.501961
// BlanchedAlmond
// Red: 255 Green: 235 Blue: 205
// Hue: 36.000000 Saturation: 1.000000 Brightness: 0.901961

Partial Active Patterns#

Active patterns that do not always produce a value are called partial active patterns; they have a return value that is an option type. To define a partial active pattern, you use a wildcard character (_) at the end of the list of patterns inside the banana clips.

Pitfalls

Mon, 01 Jan 0001 00:00:00 +0000

Shadowing#

Hiding (shadowing) a variable by misusing short declaration.

Such mistakes occur mostly inside the if-body or for-loop

var remember bool = false
 if something {
 remember := true // Wrong.
 }
// use remember

func shadow() (err error) {
 x, err := check1() // x is created; err is assigned to
 if err != nil {
 return // err correctly returned
 }

 if y, err := check2(x); err != nil { // y and inner err are created
 return // inner err shadows outer err so nil is wrongly returned!
 } else {
 fmt.Println(y)
 }
 return
}

Misusing strings#

String concatenations of the kind a += b are inefficient, especially when performed inside a loop.

Windows cmd & hotkey - 1

Wed, 09 Mar 2011 10:59:31 +1100

Do you want to make your friends amazed by your computer skill and praise you as genius? Or the hacker as watched in Sci-Fi movies? You don’t need Mac, Linux or other operating systems, just Windows, you can show-off and look like hacker and master of Zeroes and Ones, even you have no any idea of it. Here are some tricks by which you can make your friends’ jaw drop.

C# Console App

Mon, 01 Jan 0001 00:00:00 +0000

C# is an elegant and type-safe object-oriented language that enables developers to build a variety of secure and robust applications that run on the .NET Framework. C# syntax is highly expressive, yet it is also simple and easy to learn. The curly-brace syntax of C# will be instantly recognizable to anyone familiar with C, C++ or Java.

Here I am going to demonstrate how to create simple .net project without Visual Studio

F# Computations 1

Mon, 01 Jan 0001 00:00:00 +0000

Computation expressions#

Computation expressions in F# provide a convenient syntax for writing computations that can be sequenced and combined using control flow constructs and bindings. Depending on the kind of computation expression, they can be thought of as a way to express monads, monoids, monad transformers, and applicative functors. However, unlike other languages (such as do-notation in Haskell), they are not tied to a single abstraction, and do not rely on macros or other forms of metaprogramming to accomplish a convenient and context-sensitive syntax.

Template

Mon, 01 Jan 0001 00:00:00 +0000

Template#

Package template implements data-driven templates for generating textual output.
Templates are executed by applying them to a data structure. Annotations in the template refer to elements of the data structure (typically a field of a struct or a key in a map) to control execution and derive values to be displayed. Execution of the template walks the structure and sets the cursor, represented by a period ‘.’ and called “dot”, to the value at the current location in the structure as execution proceeds.

Windows cmd & hotkey - 2

Sat, 24 Mar 2012 10:59:31 +1100

This article will continue the topic of Windows command & hotkeys. Part-1 shows you common hotkeys and short command lines for Run windnow dialog. The rest of this topic will focus on the advanced commands and how to create a batch script with all those commands.

Let me clarify something first. Advanced command here does not mean that commands here are very complicated or much more powerful than common ones, which have been shown in the Part-1. Here we call them advanced, because they are used by experienced users to complete their given tasks, and those commands are used seldom by majority people. Comparing with Part-1, advanced commands have some specific features which allow them to do some special jobs, which usually are done by system admin. Advanced command is known as Admin command as well.

AWS: EKS - 1

Mon, 01 Jan 0001 00:00:00 +0000

EKS - Part 1#

Amazon Elastic Kubernetes Service (Amazon EKS) is a managed service that makes it easy for you to run Kubernetes on AWS without needing to stand up or maintain your own Kubernetes control plane. Kubernetes is an open-source system for automating the deployment, scaling, and management of containerized applications.

EKS runs Kubernetes control plane instances across multiple Availability Zones to ensure high availability.
EKS automatically detects and replaces unhealthy control plane instances.
EKS provides automated version upgrades and patching for them.
EKS is also integrated with many AWS services to provide scalability and security.

eksctl#

Install the Latest AWS CLI

F# Computations 2

Mon, 01 Jan 0001 00:00:00 +0000

Map#

Common Names: map, fmap, lift, Select

Common Operators: <$> <!>

What it does: Lifts a function into the elevated world

Signature: (a->b) -> E<a> -> E<b>.

Alternatively with the parameters reversed: E<a> -> (a->b) -> E<b>

Description “map” is the generic name for something that takes a function in the normal world and transforms it into a corresponding function in the elevated world.

An alternative interpretation of map is that it is a two parameter function that takes an elevated value E<a> and a normal function a->b, and returns a new elevated value E<b> generated by applying the function a->b to the internal elements of E<a>.

AWS: EKS - 2

Mon, 01 Jan 0001 00:00:00 +0000

EKS - Part 2#

The update process consists of Amazon EKS launching new API server nodes with the updated Kubernetes version to replace the existing ones. Amazon EKS performs standard infrastructure and readiness health checks for network traffic on these new nodes to verify that they are working as expected. If any of these checks fail, Amazon EKS reverts the infrastructure deployment, and your cluster remains on the prior Kubernetes version. Running applications are not affected, and your cluster is never left in a non-deterministic or unrecoverable state. Amazon EKS regularly backs up all managed clusters, and mechanisms exist to recover clusters if necessary. We are constantly evaluating and improving our Kubernetes infrastructure management processes.

F# Async

Mon, 01 Jan 0001 00:00:00 +0000

Async expressions#

Async expressions provide one way of performing computations asynchronously, that is, without blocking execution of other work.

Asynchronous Binding by Using let!#

The effect of let! is to enable execution to continue on other computations or threads as the computation is being performed. After the right side of the let! binding returns, the rest of the async expression resumes execution.

// let just stores the result as an asynchronous operation.
let (result1 : Async<byte[]>) = stream.AsyncRead(bufferSize)
// let! completes the asynchronous operation and returns the data.
let! (result2 : byte[]) = stream.AsyncRead(bufferSize)

let! can only be used to await F# async computations Async<T> directly. You can await other kinds of asynchronous operations indirectly:

Windows cmd & hotkey - 3

Sun, 04 May 2014 10:59:31 +1100

This article will continue the topic of Windows command & hotkeys. Part-1 shows you common hotkeys and short command lines for Run window dialog. Part-2 advanced commands and how to create a batch script with all those commands. Here I am going to show you another secret weapon in Windows system-VBScript/JScript

Breif history#

VBScript/JScript is an Active Scripting language developed by Microsoft that is modeled on Visual Basic. It allows Microsoft Windows system administrators to generate powerful tools for managing computers with error handling, subroutines, and other advanced programming constructs.

AWS: EKS - 3

Mon, 01 Jan 0001 00:00:00 +0000

EKS - Part 3#

Cluster Autoscaler#

The Kubernetes Cluster Autoscaler automatically adjusts the number of nodes in your cluster when pods fail to launch due to lack of resources or when nodes in the cluster are underutilized and their pods can be rescheduled onto other nodes in the cluster.

Strategy of auto scaling#

Stateful application

If you are running a stateful application across multiple Availability Zones that is backed by Amazon EBS volumes and using the Kubernetes Cluster Autoscaler, you should configure multiple node groups, each scoped to a single Availability Zone.

F# Task

Mon, 01 Jan 0001 00:00:00 +0000

Tasks expressions#

Asynchronous code is normally authored using async expressions. Using task expressions is preferred when interoperating extensively with .NET libraries that create or consume .NET tasks. Task expressions can also improve performance and the debugging experience. However, task expressions come with some limitations.

task { expression }

The task is started immediately after this code is executed and runs on the current thread until its first asynchronous operation is performed (for example, an asynchronous sleep, asynchronous I/O, or other primitive asynchronous operation). The type of the expression is Task<'T>, where 'T is the type returned by the expression when the return keyword is used.

AWS: EKS - 4

Mon, 01 Jan 0001 00:00:00 +0000

EKS - Part 4#

VPC Tagging#

Key: The value matches your Amazon EKS cluster’s name.
Value: The shared value allows more than one cluster to use this VPC.

Key	Value
kubernetes.io/cluster/<cluster-name>	shared

Load Balancing#

Amazon EKS supports the Network Load Balancer and the Classic Load Balancer for pods running on Amazon EC2 instance worker nodes through the Kubernetes service of type LoadBalancer. Classic Load Balancers and Network Load Balancers are not supported for pods running on AWS Fargate (Fargate).

F# Lazy

Mon, 01 Jan 0001 00:00:00 +0000

Lazy Expressions#

Lazy expressions are expressions that are not evaluated immediately, but are instead evaluated when the result is needed. This can help to improve the performance of your code.

let identifier = lazy ( expression )

Lazy expressions enable you to improve performance by restricting the execution of an expression to only those situations in which a result is needed.

To force the expressions to be performed, you call the method Force. Force causes the execution to be performed only one time. Subsequent calls to Force return the same result, but do not execute any code.

AWS: EKS - 5

Mon, 01 Jan 0001 00:00:00 +0000

EKS - Part 5#

Metrics Server#

The Kubernetes metrics server is an aggregator of resource usage data in your cluster, and it is not deployed by default in Amazon EKS clusters. The metrics server is commonly used by other Kubernetes add ons, such as the Horizontal Pod Autoscaler or the Kubernetes Dashboard.

Deploy the metrics server

 kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/download/v0.3.6/components.yaml

Verify that the metrics-server deployment

 kubectl get deployment metrics-server -n kube-system

Prometheus#

The Kubernetes API server exposes a number of metrics that are useful for monitoring and analysis. These metrics are exposed internally through a metrics endpoint that refers to the /metrics HTTP API. Like other endpoints, this endpoint is exposed on the Amazon EKS control plane.

AWS: RDS - 1

Mon, 01 Jan 0001 00:00:00 +0000

RDS#

Amazon Relational Database Service (Amazon RDS) makes it easy to set up, operate, and scale a relational database in the cloud. It provides cost-efficient and resizable capacity while automating time-consuming administration tasks such as hardware provisioning, database setup, patching and backups.

Backup & Restore SQL Server#

Backup database to S3#

Assumption
- DB name: sample_db
- S3 bucket name: sql-server-backup

Backup with built-in stored proc

 exec msdb.dbo.rds_backup_database 
 @source_db_name='sample_db', 
 @s3_arn_to_backup_to='arn:aws:s3:::sql-server-backup/sample_db_20191221.bak', 
 @overwrite_S3_backup_file=1;

Track status

Good practice - 1

Mon, 01 Jan 0001 00:00:00 +0000

Strings#

Change a character#

How to change a character in a string

str:="hello"
c:=[]byte(s)
c[0]=’c’
s2:= string(c) // s2 == "cello"

Substring#

How to take a part(substring) of a string str

substr := str[n:m]

for-loop#

How to loop over a string str with for or for-range:

// gives only the bytes:
for i:=0; i < len(str); i++ {
 … = str[i]
}
// gives the Unicode characters:
for ix, ch := range str {
 // …
}

bytes of str#

Number of bytes in a string str

Good practice - 2

Mon, 01 Jan 0001 00:00:00 +0000

Goroutines and channels#

Performance advice:

A rule of thumb if you use parallelism to gain efficiency over serial computation: the amount of work done inside goroutine has to be much higher than the costs associated with creating goroutines and sending data back and forth between them.

Using buffered channels#

Using buffered channels for performance:

A buffered channel can easily double its throughput, depending on the context the performance gain can be 10x or more. You can further try to optimize by adjusting the capacity of the channel.

Good practice - 3

Mon, 01 Jan 0001 00:00:00 +0000

Error#

How to stop a program when an error occurs:

if err != nil {
 fmt.Printf("Program stopping with error %v", err)
 os.Exit(1)
}
// OR :
if err != nil {
 panic("ERROR occurred: " + err.Error())
}

Performance best practices and advice#

Use the initializing declaration form := wherever possible (in functions).
Use bytes if possible instead of strings
Use slices instead of arrays.
Use arrays or slices instead of a map where possible (see ref. 15)
Use for range over a slice if you only need the value and not the index; this is slightly faster than having to do a slice lookup for every element.
When the array is sparse (containing many 0 or nil-values), using a map can result in lower memory consumption.
Specify an initial capacity for maps.
When defining methods: use a pointer to a type (struct) as a receiver.
Use constants or flags to extract constant values from the code.
Use caching whenever possible when large amounts of memory are being allocated.
Use template caching

Golang snippets

Mon, 01 Jan 0001 00:00:00 +0000

Convenient logging methods#

Stringer#

package main

import (
 "fmt"
)

// Animal has a Name and an Age to represent an animal.
type Animal struct {
 Name string
 Age uint
}

// String makes Animal satisfy the Stringer interface.
func (a Animal) String() string {
 return fmt.Sprintf("%v (%d)", a.Name, a.Age)
}

func main() {
 a := Animal{
 Name: "Gopher",
 Age: 2,
 }
 fmt.Println(a) // Gopher (2)
}

GoStringer#

package main

import (
 "fmt"
)

// Address has a City, State and a Country.
type Address struct {
 City string
 State string
 Country string
}

// Person has a Name, Age and Address.
type Person struct {
 Name string
 Age uint
 Addr *Address
}

// GoString makes Person satisfy the GoStringer interface.
// The return value is valid Go code that can be used to reproduce the Person struct.
func (p Person) GoString() string {
 if p.Addr != nil {
 return fmt.Sprintf(
 "Person{Name: %q, Age: %d, Addr: &Address{City: %q, State: %q, Country: %q}}", 
 p.Name, int(p.Age), p.Addr.City, p.Addr.State, p.Addr.Country)
 }
 return fmt.Sprintf("Person{Name: %q, Age: %d}", p.Name, int(p.Age))
}

func main() {
 p1 := Person{
 Name: "Warren",
 Age: 31,
 Addr: &Address{
 City: "Denver",
 State: "CO",
 Country: "U.S.A.",
 },
 }
 // If GoString() wasn't implemented, the output of `fmt.Printf("%#v", p1)` would be similar to
 // Person{Name:"Warren", Age:0x1f, Addr:(*main.Address)(0x10448240)}
 fmt.Printf("%#v\n", p1)

 p2 := Person{
 Name: "Theia",
 Age: 4,
 }
 // If GoString() wasn't implemented, the output of `fmt.Printf("%#v", p2)` would be similar to
 // Person{Name:"Theia", Age:0x4, Addr:(*main.Address)(nil)}
 fmt.Printf("%#v\n", p2)

}

// ----- Output ------
// Person{Name: "Warren", Age: 31, Addr: &Address{City: "Denver", State: "CO", Country: "U.S.A."}}
// Person{Name: "Theia", Age: 4}

File#

Read file#

func main() {
 file, err := os.Open("input.dat")

 if err != nil {
 fmt.Printf("An error occurred on opening the input file\n" +
 "Does the file exist?\n" +
 "Have you got acces to it?\n")
 return
 }
 defer file.Close()
 iReader := bufio.NewReader(file)
 for {
 str, err := iReader.ReadString('\n')
 if err != nil {
 return // error or EOF
 }
 fmt.Printf("The input was: %s", str)
 }
}

Read & Write with sliced buffer#

func cat(f *os.File) {
 const NBUF = 512
 var buf [NBUF]byte
 for {
 switch nr, er := f.Read(buf[:]); true {
 case nr < 0:
 fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", f, er)
 os.Exit(1)
 case nr == 0: // EOF
 return
 case nr > 0:
 if nw, ew := os.Stdout.Write(buf[0:nr]); nw != nr {
 fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", f, ew)
 }
 }
 }
}

TCP Client/Sever#

Client#

func main() {
 arguments := os.Args
 if len(arguments) == 1 {
 fmt.Println("Please provide host:port.")
 return
 }

 CONNECT := arguments[1]
 c, err := net.Dial("tcp", CONNECT)
 if err != nil {
 fmt.Println(err)
 return
 }

 for {
 reader := bufio.NewReader(os.Stdin)
 fmt.Print(">> ")
 text, _ := reader.ReadString('\n')
 fmt.Fprintf(c, text+"\n")

 message, _ := bufio.NewReader(c).ReadString('\n')
 fmt.Print("->: " + message)
 if strings.TrimSpace(string(text)) == "STOP" {
 fmt.Println("TCP client exiting...")
 return
 }
 }
}

Server#

func main() {
 arguments := os.Args
 if len(arguments) == 1 {
 fmt.Println("Please provide port number")
 return
 }

 PORT := ":" + arguments[1]
 l, err := net.Listen("tcp", PORT)
 if err != nil {
 fmt.Println(err)
 return
 }
 defer l.Close()

 c, err := l.Accept()
 if err != nil {
 fmt.Println(err)
 return
 }

 for {
 netData, err := bufio.NewReader(c).ReadString('\n')
 if err != nil {
 fmt.Println(err)
 return
 }
 if strings.TrimSpace(string(netData)) == "STOP" {
 fmt.Println("Exiting TCP server!")
 return
 }

 fmt.Print("-> ", string(netData))
 t := time.Now()
 myTime := t.Format(time.RFC3339) + "\n"
 c.Write([]byte(myTime))
 }
}

Ubuntu Desktop 20 LTS note

Mon, 20 Dec 2021 14:59:31 +1100

Ubuntu 20.04.3 LTS (Focal Fossa)#

Ubuntu is the world’s most popular open-source desktop operating system. Ubuntu 20.04 LTS is an enterprise-grade, secure, cost-effective operating system for organisations and home users.

Zsh Prezto#

Install Prezto#

clear
sudo apt-get install -y git
sudo apt-get update && sudo apt-get install -y zsh
# Get prezto
git clone --recursive https://github.com/sorin-ionescu/prezto.git ~/.zprezto

# Backup zsh config if it exists
if [ -f ~/.zshrc ];
 then
 mv ~/.zshrc ~/.zshrc.backup
fi

# Create links to zsh config files
ln -s ~/.zprezto/runcoms/zlogin ~/.zlogin
ln -s ~/.zprezto/runcoms/zlogout ~/.zlogout
ln -s ~/.zprezto/runcoms/zpreztorc ~/.zpreztorc
ln -s ~/.zprezto/runcoms/zprofile ~/.zprofile
ln -s ~/.zprezto/runcoms/zshenv ~/.zshenv
ln -s ~/.zprezto/runcoms/zshrc ~/.zshrc

Change theme & module#

Update the theme ‘sorin’ to ‘steeef’ in .zpreztorc
Add following plugins

zstyle ':prezto:load' pmodule \
 'environment' \
 'terminal' \
 'editor' \
 'history' \
 'directory' \
 'spectrum' \
 'utility' \
 'completion' \
 'git' \
 'syntax-highlighting' \
 'history-substring-search' \
 'prompt'

Change shell to Zsh#

chsh -s $(Which zsh)
source ~/.zshrc

Install docker#

Set up the repository#

 sudo apt-get update

 sudo apt-get install \
 ca-certificates \
 curl \
 gnupg \
 lsb-release

Add Docker’s official GPG key:#

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor \
 -o /usr/share/keyrings/docker-archive-keyring.gpg

# Use the following command to set up the stable repository. 
# To add the nightly or test repository, add the word nightly or test (or both) 
# after the word stable in the commands below. Learn about nightly and test channels.

echo \
"deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Install Docker Engine#

# Update the apt package index, and install the latest version of 
# Docker Engine and containerd, or go to the next step to install 
# a specific version:

 sudo apt-get update

 sudo apt-get install docker-ce docker-ce-cli containerd.io

Post installation of Docker#


# Create the docker group.
sudo groupadd docker

# Add your user to the docker group.
sudo usermod -aG docker $USER

# Log out and log back in so that your group membership is re-evaluated.

# On Linux, you can also run the following command to activate the changes to groups:

newgrp docker

# Test the docker
docker ps

Add Docker completion to Zsh#

Add the completion to prezto

curl -fLo ~/.zprezto/modules/completion/external/src/_docker \
https://raw.githubusercontent.com/docker/cli/master/contrib/completion/zsh/_docker

Add following line to zshrc

autoload -Uz compinit; compinit

Git#

Set git credential store#

git config credential.helper store	
# OR 
git config --global credential.helper store

Dotnet Core 6 SDK#

Add the Microsoft package signing key to your list of trusted keys and add the package repository.


wget https://packages.microsoft.com/config/ubuntu/20.04/packages-microsoft-prod.deb -O packages-microsoft-prod.deb
sudo dpkg -i packages-microsoft-prod.deb
rm packages-microsoft-prod.deb

Install the SDK

sudo apt-get update; \
 sudo apt-get install -y apt-transport-https && \
 sudo apt-get update && \
 sudo apt-get install -y dotnet-sdk-6.0

Golang#

Download & install the golang tal ball

# Download the linux tar ball from golang site
sudo rm -rf /usr/local/go && sudo tar -C /usr/local -xzf go1.17.5.linux-amd64.tar.gz

Set the Go to PATH on file .zshrc

export PATH=$PATH:/usr/local/go/bin

Verify the version

go version

Rustlang#

Use universal script

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Java: OpenJDK#

Install LTS JDK

 sudo apt install -y openjdk-8-jdk \
 openjdk-11-jdk \
 openjdk-17-jdk

Setup default JDK

sudo update-alternatives --config java

Angular 9 CRM Starter Project

Fri, 07 Feb 2020 16:56:21 +1100

Key Takeaways#

Angular 9 is here now.
Angular Material 9 is ready as well.
Reusable starter project

Summary#

Ng-Crm > A reusable CRM starter project for real-world business based on Angular 9, Angular-Material 9.x.

This project was generated with Angular CLI version 9.x. The goal of this project is to create reusable project for real-world business. To achieve this target, we need a solution which includes simple authentication process, restful API feature with token support and simple but elegant UI design.

Docker Kits

Sat, 07 Dec 2019 16:56:21 +1100

Docker Kits#

The repository is the collection of kits built on the top of docker image. At the very begiinning, the repository was built for kits used for infrastructure. It is about to expand the scope from infrastructure to simplify the integration test, even build for speical development.

Repository name in Docker Hub: harryh00/docker-kits

Why chooses docker#

Docker is a tool designed to make it easier to create, deploy, and run applications by using containers. Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and deploy it as one package.

Amazon Linux 2

Tue, 04 Dec 2018 14:59:31 +1100

Amazon Linux 2#

Amazon Linux 2 is the next generation of Amazon Linux, a Linux server operating system from Amazon Web Services (AWS). It provides a secure, stable, and high performance execution environment to develop and run cloud and enterprise applications. With Amazon Linux 2, you get an application environment that offers long term support with access to the latest innovations in the Linux ecosystem. Amazon Linux 2 is provided at no additional charge.

SFTP & GPG

Tue, 04 Dec 2018 14:59:31 +1100

SFTP#

SFTP (SSH File Transfer Protocol) is a secure file transfer protocol. It runs over the SSH protocol. It supports the full security and authentication functionality of SSH.

SFTP has pretty much replaced legacy FTP as a file transfer protocol, and is quickly replacing FTP/S. It provides all the functionality offered by these protocols, but more securely and more reliably, with easier configuration. There is basically no reason to use the legacy protocols any more.

VPN StrongSwam setup

Tue, 04 Dec 2018 14:59:31 +1100

VPN StrongSwan#

strongSwan is a multiplatform IPsec implementation. The focus of the project is on strong authentication mechanisms using X.509 public key certificates and optional secure storage of private keys and certificates on smartcards through a standardized PKCS#11 interface and on TPM 2.0.

Launch an instance with Ubuntu#

Update setup script#

Following is setup.sh

#!/bin/bash
usage() {
 echo "Usage: strongswan.sh [install|start] [PATADDR] [ETHDEV]

 'install' parameters:
 PATADDR The private address on MARKETNET (eg. 172.17.133.10)
 ETHDEV The name of the local ethernet device (eg. etho)
 "
 exit 1
}


install_function () {
 apt update -y
 apt install strongswan -y
 cp ipsec.conf /etc/ipsec.conf
 cp ipsec.secrets /etc/ipsec.secrets
 sysctl -w net.ipv4.ip_forward=1
 ip addr add 172.17.12.127 dev eth0
 iptables -t nat -F
 iptables -t nat -I POSTROUTING -m policy --pol ipsec --dir out -j ACCEPT
 iptables -t nat -A POSTROUTING -d 146.164.46.0/24 -j SNAT --to 172.17.12.127
 iptables-save
}

start_function () {
 ipsec reload
 ipsec rereadsecrets
 ipsec up remote-vpn-b
 ipsec down remote-vpn-b
 ipsec up remote-vpn-a
 ipsec down remote-vpn-a
}

if [ $# -lt 1 ]; then
 echo "No command"
 usage
fi


export operation=$1

if [ "$operation" = "install" ]; then
 install_function
elif [ "$operation" = "start" ]; then
 start_function
fi

Update IPSec config#

config setup
 strictcrlpolicy=no
 uniqueids = no
 charondebug="ike 3,dmn 0, mgr 3, chd 2, cfg 2, knl 0, net 2, enc 0, esp 3"

conn %default
 auto=route
 compress=no
 type=tunnel
 keyexchange=ikev2
 ike=aes256-sha512-modp2048
 esp=aes256-sha512-modp2048
 leftauth=psk
 rightauth=psk
 authby=secret
 lifetime=28800
 ikelifetime=28800
 rekey=yes
 reauth=no
 inactivity=1800
conn remote-vpn-a
 left=%defaultroute
 leftsubnet=172.17.12.127/32
 leftid=13.31.131.113
 right=202.22.20.2
 rightid=202.22.20.2
 rightsubnet=146.164.46.0/24
conn remote-vpn-b
 left=%defaultroute
 leftsubnet=172.17.12.127/32
 leftid=13.31.131.113
 right=202.22.22.2
 rightid=202.22.22.2
 rightsubnet=146.164.46.0/24

Update IPSec secrets#

13.31.131.113 202.22.20.2 : PSK Your_Remote_Key
13.31.131.113 202.22.22.2 : PSK Your_Remote_Key

Setup & Test StrongSwan#

sudo bash strongswan.sh install
sudo ipsec reload
sudo ipsec rereadsecrets
sudo ipsec up remote-vpn-b
sudo ipsec down remote-vpn-b
ipsec up remote-vpn-a
sudo ipsec up remote-vpn-a
ipsec up remote-vpn-b
sudo ipsec up remote-vpn-b

VPN VyOS setup

Tue, 04 Dec 2018 14:59:31 +1100

VPN VyOS#

VyOS is a fully open source network OS that runs on a wide range of hardware, virtual machines, and cloud providers and offers features for any networks, small and large.

VyOS on AWS#

Setup VyOS#

Launch instance with community AMI - VyOS (HVM) 1.x.x
Customize the setup script

#!/bin/bash
source /opt/vyatta/etc/functions/script-template

AWS_PRIVATE_IP=10.104.16.128
AWS_PUBLIC_IP=13.14.15.16
AWS_NAT_SUBNET=10.104.0.0/16
REMOTE_NAT_IP=127.17.12.172
REMOTE_VPN_SUBNET=146.164.46.0/24
REMOTE_1ST_VPN_IP=202.22.20.2
# REMOTE_2ND_VPN_IP=202.22.2.20 # redundant connection not currently used
REMOTE_PRE_SHARED_KEY=Your_Remote_Key

# begin configuration
configure

# input settings using set
set system host-name vyos-vpn

# setting up NAT
set interfaces ethernet eth0 description 'aws-internal'
# create dummy ethernet device to represent REMOTE-provided private IP
set interfaces dummy dum0 address ${REMOTE_NAT_IP}/32
set interfaces dummy dum0 description 'remote-vpn-ip'
# configure SNAT
set nat source rule 100 description 'Internal to REMOTE'
set nat source rule 100 destination address ${REMOTE_VPN_SUBNET}
set nat source rule 100 outbound-interface 'any'
set nat source rule 100 source address ${AWS_NAT_SUBNET}
set nat source rule 100 translation address ${REMOTE_NAT_IP}

# setting up VPN
# set primary ethernet interface as the VPN interface
set vpn ipsec ipsec-interfaces interface 'eth0'
set vpn ipsec nat-traversal 'enable'
set vpn ipsec logging log-modes 'all' 
# esp-group
set vpn ipsec esp-group vpn-nat-esp compression 'disable'
set vpn ipsec esp-group vpn-nat-esp lifetime '28800'
set vpn ipsec esp-group vpn-nat-esp mode 'tunnel'
set vpn ipsec esp-group vpn-nat-esp pfs 'dh-group2'
set vpn ipsec esp-group vpn-nat-esp proposal 1 encryption 'aes256'
set vpn ipsec esp-group vpn-nat-esp proposal 1 hash 'sha1'
# ike-group
set vpn ipsec ike-group vpn-nat-ike ikev2-reauth 'no'
set vpn ipsec ike-group vpn-nat-ike key-exchange 'ikev1'
set vpn ipsec ike-group vpn-nat-ike lifetime '28800'
set vpn ipsec ike-group vpn-nat-ike proposal 1 encryption 'aes256'
set vpn ipsec ike-group vpn-nat-ike proposal 1 hash 'sha512'
set vpn ipsec ike-group vpn-nat-ike proposal 1 dh-group '5'
set vpn ipsec ike-group vpn-nat-ike dead-peer-detection action 'restart'
set vpn ipsec ike-group vpn-nat-ike dead-peer-detection interval '30'
set vpn ipsec ike-group vpn-nat-ike dead-peer-detection timeout '30'
# site-to-site peer
edit vpn ipsec site-to-site peer ${REMOTE_NSW_VPN_IP}
set authentication mode 'pre-shared-secret'
set authentication pre-shared-secret ${REMOTE_PRE_SHARED_KEY} 
set authentication id ${AWS_PUBLIC_IP}
set connection-type 'initiate'
set default-esp-group 'vpn-nat-esp'
set ike-group 'vpn-nat-ike'
set ikev2-reauth 'inherit'
set local-address ${AWS_PRIVATE_IP}
set tunnel 0 local prefix ${REMOTE_NAT_IP}/32
set tunnel 0 remote prefix ${REMOTE_VPN_SUBNET}

# commit command applies changes to VyOS device
commit
# save configuration to machine
save
# exit configuration mode
exit
# check status of VPN tunnel
show vpn ipsec sa
# commands to check VPN status/logs/information:

# monitor vpn ipsec
# show vpn debug
# show log vpn ipsec

Update VyOS config#

Manual update the key Your_Remote_Key or remote IP, e.g. 202.22.20.2

interfaces {
 dummy dum0 {
 address 127.17.12.172/32
 address 172.17.130.96/32
 description remote-vpn-ip
 }
 ethernet eth0 {
 address dhcp
 description aws-internal
 duplex auto
 hw-id 06:73:3f:28:dd:68
 smp_affinity auto
 speed auto
 }
 loopback lo {
 }
}
nat {
 source {
 rule 100 {
 description "Internal to REMOTE"
 destination {
 address 146.164.46.0/24
 }
 outbound-interface any
 source {
 address 10.104.0.0/16
 }
 translation {
 address 127.17.12.172
 }
 }
 }
}
service {
 ssh {
 disable-password-authentication
 port 22
 }
}
system {
 config-management {
 commit-revisions 20
 }
 console {
 device ttyS0 {
 speed 9600
 }
 }
 host-name vyos-vpn
 login {
 user vyos {
 authentication {
 encrypted-password "*"
 plaintext-password ""
 public-keys aws.vpn.vyos.key.io-bd:dc:ae:d6:28:b3:5f:5b:2e:43:6f:31:b8:b3:a0:58 {
 key AAAA1234SDjsfwfsfowerudhfhdGV/V1OEqvlpeTM49TyYmGBXzq/6262fsdfyhSOHND+USFHSDGF056nvz+ilB5HcCl/+FUig3sONKKWElxK8O/oUEurERsif+IJynsdfuyhn7ndhfdfhjlshdlfhGA+Z30knWV2QDRiID52U60YijvG4wEWwOf1xEOisccbH+09fdhfbdbfHSF/3Pt0b0uafoySi5yhCX6iuhjavl5p/Rsidfysd534sdfGHdpofygeylsdgflshsFGVNSUDF/rnpludfEqjJe/75TU026vD7A7dNn816iLVnsK+NsjrT8OtXUyGzy403
 type ssh-rsa
 }
 }
 level admin
 }
 }
 ntp {
 server 0.pool.ntp.org {
 }
 server 1.pool.ntp.org {
 }
 server 2.pool.ntp.org {
 }
 }
 package {
 auto-sync 1
 repository community {
 components main
 distribution helium
 password ""
 url http://packages.vyos.net/vyos
 username ""
 }
 }
 syslog {
 global {
 facility all {
 level notice
 }
 facility protocols {
 level debug
 }
 }
 }
 time-zone UTC
}
vpn {
 ipsec {
 esp-group vpn-nat-esp {
 compression disable
 lifetime 28800
 mode tunnel
 pfs dh-group14
 proposal 1 {
 encryption aes256
 hash sha256
 }
 }
 ike-group vpn-nat-ike {
 dead-peer-detection {
 action restart
 interval 30
 timeout 30
 }
 ikev2-reauth no
 key-exchange ikev1
 lifetime 28800
 proposal 1 {
 dh-group 14
 encryption aes256
 hash sha256
 }
 }
 ipsec-interfaces {
 interface eth0
 }
 logging {
 log-modes all
 }
 nat-traversal enable
 site-to-site {
 peer 202.22.20.2 {
 authentication {
 id 13.14.15.16
 mode pre-shared-secret
 pre-shared-secret Your_Remote_Key
 }
 connection-type initiate
 default-esp-group vpn-nat-esp
 ike-group vpn-nat-ike
 ikev2-reauth inherit
 local-address 10.104.16.128
 tunnel 0 {
 allow-nat-networks disable
 allow-public-networks disable
 local {
 prefix 127.17.12.172/32
 }
 remote {
 prefix 146.164.46.0/24
 }
 }
 }
 }
 }
}

Reboot the VyOS

_vyatta_op_run reboot

Dual Boot Windows 10 & Ubuntu 18

Fri, 30 Nov 2018 14:59:31 +1100

Dual boot Ubuntu 18 with Windows 10#

I have a couple Linux workstations, but all of them are old PC or laptop. Today I get a chance to test Ubuntu on a brand new laptop. Here I are going to write down all I did to create this dual boot laptop

Caution#

The laptop I worked on is Lenovo IdeaPad S model with UEFI firmware, but it doesn’t mean all Lenovo laptops will work in the same way, not to mention other brand’s laptop. So before you try anything, please backup all your data first.

Ubuntu Desktop 18 LTS note

Wed, 04 Jul 2018 14:59:31 +1100

Prelude#

This article is mainly to record the stuff to do post Ubuntu Desktop 18.04 Installation.

Purpose#

All actions post installation is to make the Ubuntu Desktop a wonderful toolkit for developer.

Prerequisite#

Install all essentials

sudo apt install -y git curl
sudo apt-get install -y apt-transport-https ca-certificates gnupg-agent
sudo apt install -y software-properties-common

Install & Setup Zsh#

Install Zsh

sudo apt install -y zsh

Setup Zsh

I prefer Prezto Zsh, which is the minimal version of Oh-My-Zsh. In my opinion, Oh-My-Zsh is kind of slow and sort of overblown.

Raspberry Pi setup

Sat, 06 Jan 2018 14:59:31 +1100

Prelude

*This note is mainly to record how to setup Raspberry Pi as file server.

Prerequisites#

You have a Raspberry Pi with pre-installed raspbian SD card
You are happy to get your hands dirty
You have some basic computer concept.
RPi is short for Raspberry Pi

My Raspberry Pi is a bit old#

I only have the RPi 1 model B with pre-installed raspbian SD card in place. It is quite outdated. If you don’t know the model of your RPi, please don’t worry it now. I will explain how to get the info later. I got this RPi as a gift 2 years ago. I left it in the garage and totally forgot it, until I cleaned up my garage a couple months ago. Actually I loved the old model with transparent plastic box more than the new one. I knew if I continued to leave it in the garage, it would be a rubbish soon, because it is not easy to find some equipment or software compatible with the old RPi. Luckily the lifespan of RPi is much longer than the mobile phone, but it still took me some effort to setup the wifi adapter.

Lubuntu 16 desktop

Thu, 04 Jan 2018 13:59:31 +1100

Prelude

There is no big difference against setup between Lubuntu and Ubuntu. I just want to keep a latest version of setup for myself as reference

Prerequisites#

You have Lubuntu 16 in place
Internet is available

UFW setup#

sudo ufw enable
sudo ufw allow 80/tcp
sudo ufw allow ssh
sudo ufw allow 443/tcp
sudo ufw allow 8000/tcp

SSH server setup#

!!! For production environment, SSH should be secured by the CA

Try Minikube

Wed, 11 Oct 2017 11:59:31 +1100

Prerequisites#

Install KVM or VirtualBox
Install Ubuntu / Debian on KVM or VirtualBox
Install Minikube

Check K8s version and config#

kubectl version
kubectl config
kubectl cluster-info

Get / Describe command#

kubectl get ndoes
kubectl get pods
kubectl get deployments
kubectl get services

kubectl describe pods

Deploy hello-world node demo app#

Deploy a demo app

kubectl run kubernetes-bootcamp --image=gcr.io/google-samples/kubernetes-bootcamp:v1 --port=8080

# View deployments and pods
kubectl get deployments
kubectl get pods

Pods that are running inside Kubernetes are running on a private, isolated network. By default they are visible from other pods and services within the same kubernetes cluster, but not outside that network.

Grub Trouble Shooting

Wed, 20 Sep 2017 14:59:31 +1100

Change BIOS

Start your PC by pressing a pressing a special function key (usually F12, F10 or F2 depending on the vendor specifications).
Some PC’s BIOS has BOOT tab option, open the BOOT tab, you will find the OS Boot Manager. It is the simplest way to fix the issue. If your PC’s BIOS has no such setting feature, you need to check the next section.

Change the Windows Boot Manager

FlatApi - Restful API for python dev

Thu, 03 Aug 2017 16:56:21 +1100

Summary#

FlatApi is a zero coding and zero configuration restful API server inspired by Json-Server_ and Eve_. It is designed to be used as fake restful api for development, especially for people want to use Python stack. Setup process is less than 10 seconds.

FlatApi#

Zero coding and configuration to setup Restful API FlatApi is designed to use without coding and configuration by default. You just need one config to setup all endpoints you need, then you can use it immediately.

Angular vs React vs Vue

Wed, 07 Jun 2017 16:56:21 +1100

Angular, React, Vue as most popular JavaScript frameworks at present, we just discuss Angular 1.x, Angular 2 / 4, React 15+ (Redux), and Vue 2+ here. There is no Angular 3, if you have not noticed before.

Client side is a battle field#

In past 6–8 years, the Restful API has been accepted as one of standard web interfaces for most web applications, solution architect can simply add REST API on the top of existing web layer or business layer to provide REST API and support multiple client devices. So the developers can continue to develop or maintain system with their favorite programming language, framework or technical stacks.

Ubuntu 16 server note

Thu, 04 May 2017 14:59:31 +1100

Prelude

This article is mainly to help experienced user install and setup Ubuntu 16 LTS Server. If you are looking for the information for Ubuntu 14, please go to the page Ubuntu 14 server setup

Prerequisites#

You are familiar with Ubuntu, at least you have some experience working on Linux system.
You are familiar with basic bash/shell command

Wireless Setup#

If you install ubuntu server on a laptop, you might end up to setup the wifi first. Usually you won’t bring the cable with your laptop wherever you go, also you might just have no cable or run out all cables. Now let’s dive into how to setup the wifi on sever.

Create a blog site on GitHub Pages

Wed, 15 Feb 2017 14:59:31 +1100

If you use Unix-style system, I recommend you to follow the Hugo Quick Start and Hosting on GitHub Pages to create a blog to GitHub pages within 5 mins.

When I decided to use hugo to create a blog on GitHub pages from my windows machine, it took me over 30 mins. I hope this blog can help someone want to do sth similar within Windows environment.*

Step 1 - Plan and prepare#

Prerequisite#

You already have Hugo on your computer. If not, please follow the instruction to install hugo on Windows.

Manage your github repositories#

You will have two repositories blog-hugo and <username>.github.io repositories to hold your hugo content and blog site respectively.

CentOS 7 Server

Fri, 03 Feb 2017 10:59:31 +1100

Prelude

This article is mainly to help experienced user install and setup CentOS 7 Server.

Prerequisites#

You are familiar with CentOS, at least you have some experience working on Linux system.
You are familiar with basic bash/shell command

Things to do after installing CentOS server#

How to setup your server

Firewall setup#

sudo firewall-cmd --permanent --add-port=22/tcp
sudo firewall-cmd --permanent --add-port=21/tcp
sudo firewall-cmd --permanent --add-port=80/tcp
sudo firewall-cmd --permanent --add-port=443/tcp
sudo firewall-cmd --permanent --add-port=8080/tcp

sudo firewall-cmd --reload

SSH server setup#

!!! For production environment, SSH should be secured by the CA

Angular 4 CRM Project

Wed, 07 Dec 2016 16:56:21 +1100

Summary#

Ng4Crm is reusable CRM project for real-world business based on Angular 4, Angular-Material & Bootstrap 3.

This project starts from a popular starter project AngularClass/AngularStarter. The goal of this project is to create reusable project for real-world business. To achieve this target, we need a solution which should include authentication process, restful API feature with token support and simple but elegant UI design.

Features#

This project is built on the top of AngularClass/Angular-Starter.

CNTK Note - 1

Wed, 07 Dec 2016 16:56:21 +1100

Prerequisites#

You are using Windows 7 or higher version
You are using Anaconda to setup the environment

Create CNTK virtual environment#

use follow command to remove existing virtual environment#

 conda remove -n cntk --all
 conda create -n cntk

Activate virtual environment and install CNTK#

activate cntk
pip install https://cntk.ai/PythonWheel/CPU-Only/cntk-2.0rc3-cp36-cp36m-win_amd64.whl

Test CNTK#

python
>>> import cntk
>>> cntk.__version__
'2.0rc3'

Laravel MVC Starter

Wed, 07 Dec 2016 16:56:21 +1100

Summary#

This starter is the starting point of laravel 5 MVC project. This application is meant to be used as a starting place for those looking to get their feet wet with laravel.

Overview of project#

BDD ( Business domain design)#

+-------+ 0...* 0...* +--------+ 1 0...* +---------+ 
| tag | --------------- | post | ----- ----- | comment |
+-------+ +--------+ +---------+ 
 | 1...*
 |
 | 0...*
 +--------+ 
 | like |
 +--------+

Structure of starter#

\path\to\lara-mvc-starter
+---app <-// Customized PHP application code
| +---Console
| +---Exceptions
| +---Http
| | +---Controllers
| | | \---Auth
| | \---Middleware
| \---Providers
+---bootstrap <-// bootstrap the framework and configure autoloading
| \---cache
+---config <-// application configuration
+---database <-// database migration files
| +---factories
| +---migrations
| \---seeds
+---public <-// Distributed website folder including Style sheet
+---resources <-// View files, Javascripts, localization setting
| +---assets
| +---lang
| \---views
| +---admin
| +---blog
| +---errors
| +---layouts
| +---other
| +---partials
| \---vendor
| \---pagination
+---routes <-// Route definitions and setting
+---storage <-//Blade templates, file based sessions, file caches
| +---app
| | \---public
| +---framework
| | +---cache
| | +---sessions
| | \---views
| \---logs
+---tests
\---vendor <-// Laravel framework

Screenshots#

React Redux CRM Project

Wed, 07 Dec 2016 16:56:21 +1100

Summary#

React-Crm is reusable CRM starter project for real-world business based on React 15.4, React-Redux & Material-UI.

The goal of this starter project is to create reusable project for real-world business. To achieve this target, we need a solution which should include authentication process, restful API feature with token support and simple but elegant UI design.

Features#

This project is built on the top of React/Redux.
The UI part of this project uses Material-UI.

Tensorflow Note - 1

Wed, 07 Dec 2016 16:56:21 +1100

TensorFlow is an end-to-end open source platform for machine learning. It has a comprehensive, flexible ecosystem of tools, libraries and community resources that lets researchers push the state-of-the-art in ML and developers easily build and deploy ML powered applications.

Prerequisites#

You are using Ubuntu 16
Your machine has Nvidia GPU card installed
If you are using Ubuntu 14, the installation of CUDA and cuDNN will be a bit different. Please check Google’s instructions.

Install python3 and pip3#

Please find instructions here

Install virtualenv via pip3#

pip3 install virtualenv

Create two tensorflow virtualenvs.#

mkdir ~/.envs
virtualenv --system-site-packages ~/.envs/tf ### CPU only
virtualenv --system-site-packages ~/.envs/tfgpu ### GPU enabled

Install tensorflow for different virtualenvs#

source ~/.envs/tf/bin/activate
source ~/.envs/tfgpu/bin/activate

pip3 install tensorflow ### CPU only
pip3 install tensorflow-gpu ### GPU enabled

Install CUDA and cuDNN for tensorflow-gpu#

Use following command to check you GPU information

Tensorflow Note - 2

Wed, 07 Dec 2016 16:56:21 +1100

Prerequisites#

You are using Windows 7 or higher version
You are using Anaconda to setup the environment

Install Anaconda#

Anaconda® is a package manager, an environment manager, a Python/R data science distribution, and a collection of over 1,500+ open source packages. Anaconda is free and easy to install, and it offers free community support.

Please download Anaconda from the official site

Create tensorflow virtualenv with python 3.5#

Anaconda uses python 3.6 by default. Tensorflow only supports python 3.5.

Vue 2 Admin Project

Wed, 07 Dec 2016 16:56:21 +1100

Summary#

Vue2Admin is a fully responsive admin template that is inspired by AdminLTE.

Features#

This template is built-in with Vue 2 at the start.
It include Vue Resource, Vuex as well.
The plugins for this project are loaded with script loader.

Structure of Reetek Vue2Admin#

path\to\vue2admin
+---build <-// webpack files
+---config <-// configuration of dev or prod environment
+---screenshots
+---src <-// vue components 
| +---components
| | +---charts
| | +---dashboard
| | +---forms
| | +---mailbox
| | +---misc
| | +---pages
| | +---tables
| | +---ui
| | \---widget
| \---filters
+---static <-// css, dump data, fonts, image files and plugins
| +---css
| +---data
| +---fonts
| +---img
| | +---credit
| | \---stock
| \---js
| \---plugins <-// plugins for admin dashboard 
| +---AdminLTE
| +---bootstrap
| +---bootstrap-slider
| +---bootstrap-wysihtml5
| +---chartjs
| +---ckeditor
| + ...
\---test
 +---e2e
 \---unit

Screenshots#

Vue 2 CRM Project

Wed, 07 Dec 2016 16:56:21 +1100

Summary#

Vue2Crm is a reusable Vue.js CRM starter project for real-world business based on Vue 2 PWA template with Vuetify.

The goal of this project is to create a reusable project for real-world business. To achieve this target, we need a solution which includes authentication process, restful API feature and simple but elegant UI design.

Features#

This starter project is built-in with Vue 2 PWA from scratch.
The whole UI is built on the Vuetify
It includes Vuex, Axios as well.
It uses Json-Server as fake Restful API. (You can simple replace it with your own API)

Structure of Vue2Crm#

path\to\vue2crm
+---build <-// webpack files
+---config <-// configuration of dev or prod environment
+---db <-// json files for json-server
| +---db.json <-// dummy db
| \---routes.json <-// configure fake restful api
+---screenshots
+---src <-// vue components 
| +---components
| | +---404.vue
| | +---About.vue
| | +---Customers.vue
| | +---Customer.vue
| | +---Orders.vue
| | +---Order.vue
| | +---Login.vue
| | \---...
| +---router <-// vue-router
| +---utils
| | +---auth.js <-// auth service
| | +---backend-api.js <-// Axios instance 
| | +---store.js <-// Vuex
| \---stylus <-// Customize stylus
+---static <-// css, fonts, image files
| +---img
| \---manifest.json <-// PWA manifest file
\---test
 +---e2e
 \---unit

Screenshots#

Angularjs Webpack ES6 Starter

Tue, 15 Nov 2016 16:56:21 +1100

Summary#

It simply includes font-awesome, bootstrap for the people who don’t want to use boostrap-webpack, font-awesome-webpack. I find it saves us so much effort to create prototype, since we don’t need spectacular UI.

This starter uses angular 1.5 for someone want to build component.
This repo follows mvc patterns instead of component pattern.
ES6, and ES7 support with babel.
Development server with live reload.
Production builds with cache busting.
Testing environment using karma to run tests and jasmine as the framework.
Code coverage when tests are run.
Include font-awesome without font-awesome-loader.
Include Bootstrap 3 without bootstrap-loader.
No gulp and no grunt, just npm scripts.

Structure of starter#


\path\to\angularjs-webpack-es6-starter
| .babelrc <-// default setting es2015.
| karma.conf.js <-// tests and report setup 
| webpack.config.js <-// webpack config
\---src
 | tests.webpack.js
 | 
 +---app
 | | app.html <-// app view
 | | app.js <-// app module
 | | app.routes.js <-// app route to manage all routes 
 | | app.runner.js <-// app runner for state change enhancement 
 | | app.spec.js <-// app spec file for testing 
 | | 
 | +---common <-// common module for whole app
 | | | common.js
 | | | common.spec.js
 | | +---directives <-// common directives for whole app
 | | | appUiDirectives.js
 | | | appUiDirectives.spec.js
 | | | commonDirectives.js
 | | | commonDirectives.spec.js
 | | +---services <-// common views for whole app
 | | | ApiService.js
 | | | ApiService.spec.js
 | | | UtilService.js
 | | | UtilService.spec.js
 | | \---views <-// contains common views
 | | footer-view.html
 | | header-view.html
 | | sidebar-view.html
 | | topbar-view.html
 | \---main <-// built-in fonts, css, images 
 | \---dashboard
 | +---controllers
 | | dashboardController.js
 | | dashboardController.spec.js
 | \---views
 | dashboard-view.html
 | 
 +---public <-// built-in fonts, css, images 
 | | index.html
 | +---fonts
 | | +--- ...
 | \---img
 | +--- favicon.ico
 \---style <-// css files including customized css

Browse Repository #

Git Practices

Thu, 11 Aug 2016 11:59:31 +1100

Push existing repository to remote#

Update the remote git url

 $ git remote set-url origin [your_new_repo_url]

Push it remote branch master/main
```
 $ git push -uf origin [master/main]
```

Create a new branch with git#

Create the branch locally#

Create the branch on your local machine and switch in this branch
```
 $ git checkout -b [name_of_your_new_branch]
```

Push the branch#

Push the branch on git-repository (Github, Bitbucket)

PHP Web Framework

Thu, 11 Aug 2016 11:59:31 +1100

Here we are going to explore some PHP web frameworks.

PHP development environment setup#

Install PHP 5.6.x#

Please find the instruction from home page
Composer

Linux#

Use curl -s https://getcomposer.org/installer | php -- to install composer on Linux
use ‘composer -v ’ to verify.

Windows#

Download the composer and install php on your PC
Use composer -v to verify the composer is ready.

Zend Framework#

Zend Framework 2.x is a collection of 60+ packages for professional PHP development. It can be used to develop web applications and services using PHP 5.6+, and provides 100% object-oriented code using a broad spectrum of language features.

Build mobile app with web tech

Sun, 10 Jul 2016 14:59:31 +1100

What is mobile app#

A mobile application, basically, is a computer generated program designed and developed to run on iPhone, Android Smartphone, and many other mobile devices. In a nutshell, there are three types of apps

Native apps are specific to a given mobile platform (iOS or Android) using the development tools and language that the respective platform. Usaully it looks and performs the best.

HTML5 apps use standard web technologies—typically HTML5, JavaScript and CSS. This write-once-run-anywhere approach to mobile development creates cross-platform mobile applications that work on multiple devices.

Azure Practices

Sun, 10 Apr 2016 14:59:31 +1100

Here we are going to explore how to deploy web applications to Azure. From sep 2015, Microsoft launched new portal for Azure. To be honest, new portal is amazing, IMO, it is one of best changes from Microsoft.

Prerequisites#

You have experience with .net web applications.
You have experience with website or web app deployment.

Getting Started#

Register a Microsoft account. e.g. live.com, outlook.com, etc.
Start free trial account on Azure cloud
Install Azure powershell, Azure CLI, Azure SDK for Visual Studio

App Service#

Web app#

Create a website from portal

Ubuntu 14 -- server setup

Fri, 04 Mar 2016 14:59:31 +1100

Prelude

This article is mainly to help experienced user install and setup Ubuntu server. If you are not familiar with Ubuntu system, please install Ubuntu desktop version at first, and you can follow Ubuntu deskstop setup

Prerequisites#

You are familiar with Ubuntu, at least you have some experience working on Linux system.
You are familiar with bash/shell script
You are going to setup Ubuntu server for special purpose. e.g. Web server, file server, or data center.

UFW setup#

sudo ufw enable
sudo ufw allow 80/tcp
sudo ufw allow ssh
sudo ufw allow 443/tcp
sudo ufw allow 8000/tcp

SSH server setup#

Secure SSH with CA in production#

sudo apt-get install openssh-server 

## backup default config 
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.factory-defaults
sudo chmod a-w /etc/ssh/sshd_config.factory-defaults

## use any editor to update sshd_config 
sudo nano /etc/ssh/sshd_config

## uncomment PasswordAuthentication yes to allow remote password login
## Password authentication is only for test environment

## setup ssh auto-start onboot
sudo update-rc.d ssh defaults

Time Zone setup#

sudo dpkg-reconfigure tzdata

install software-properties-common Package#

software-properties-common python-software-properties

Install byobu screen

Zend Framework 2 MVC Starter

Tue, 09 Feb 2016 16:56:21 +1100

Summary#

This starter is the starting point of zend framework 2 MVC project. This application is meant to be used as a starting place for those looking to get their feet wet with ZF2.

Features#

This starter was built on the zend framework 2.x.
This starter uses mysql as database setting by default.
Include digest authentication by default.
Include font-awesome files.
Include Bootstrap 3 without bootstrap-loader.
Include html5shiiv.js to support older IE browser.

Structure of starter#


\path\to\zf2-mvc-starter
+---config // Database, authorizaion, authentication setting
+---data 
+---module // Customized application sources
| +---Application // Global module used by whole application
| | +---config
| | | \---module.config.php // Register all modules 
| | +---language
| | +---src
| | | \---Application
| | | +---Controller
| | | \---Factory
| | | \---AuthenticationAdapterFactory.php
| | \---view // Contains common master, basic layout files 
| | +---application
| | | \---index
| | +---error
| | +---layout
| | \---partial
| +---BookList // Customized module for business purpose
| | +---config
| | +---src
| | | \---BookList
| | | +---Controller
| | | +---Form
| | | \---Model
| | \---view
| | \---book-list
| | \---book
| \---Test
| \---config
+---public // Contains all fonts, css, images, and js files
| +---css
| +---fonts
| +---img
| \---js
\---vendor // Contains Zend Framework 2 source code

Screenshot of home page#

Ubuntu 14 -- desktop setup & dual boot

Sun, 10 Jan 2016 14:59:31 +1100

This article is mainly to help beginner install Ubuntu desktop at the first time. If you are looking for setup of Ubuntu server, please check out the blog – Ubuntu server setup

Where to install Linux?#

How to answer this quetion really depends user’s computer knowledge and skills. Basically Linux can be installed on almost any PC, laptop, embedded device or tablet. So there are some suggestions for people with different level skills.*

Ubuntu 14 -- desktop, extra tools

Sun, 10 Jan 2016 14:59:31 +1100

Prerequisites#

Install Ubunt 14 Desktop
Internet is availble

Install chrome#

wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
sudo dpkg -i google-chrome-stable_current_amd64.deb

Install Umake#

sudo add-apt-repository ppa:ubuntu-desktop/ubuntu-make
sudo apt-get update
sudo apt-get install ubuntu-make

Install IDEs via Umake#

umake ide pycharm
umake web visual-studio-code
umake android android-studio

General prerequest#

sed -i "/^## deb .*partner/ s/^## //" /etc/apt/sources.list && apt-get update
sudo apt-get install geany byobu p7zip-full gimp pdfshuffler scribus \
filezilla lftp ubuntu-restricted-extras vlc pyrenamer \
imagemagick hugin darktable skype avidemux

Remove Games#


sudo apt-get remove aisleriot gnome-mahjongg gnomine gnome-sudoku

Geany themes#

cd ~/Downloads
git clone https://github.com/codebrainz/geany-themes.git
mkdir ~/.config/geany/colorschemes
cp ~/Downloads/geany-themes/colorschemes/* ~/.config/geany/colorschemes/
rm -rf ~/Downloads/geany-themes

Cloud#

from: http://www.webupd8.org/2014/06/install-copycom-client-in-ubuntu-or.html

Macbook Notes - Intel X64

Sun, 12 Jul 2015 14:59:31 +1100

Prerequisites#

Mac OS 10.12+
Intel X64 CPU

Ownership issue#

If you have Homebrew or other software installed by someone else, you need to change ownership

sudo chown -R $(whoami) /usr/local/brew
sudo chown -R $(whoami) /usr/local/etc
sudo chown -R $(whoami) /usr/local/share
sudo chown -R $(whoami) /usr/local/lib

Install Homebrew#

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"

## Brew commands

brew update
brew upgrade 
brew list

The cask is no longer a brew command from 2021. The command has changed as below

JavaScript and OOP

Thu, 20 Mar 2014 14:59:31 +1100

Prerequisites#

You should have basic knowledge of Javascript and Object Oriented Programming.
You should know how to test sample code on Chrome or Firefox. It is simple, just open your browser and click F12, copy the code to console and then press Enter.

What is JavaScript?#

JavaScript, not to be confused with Java, was created in 10 days in May 1995 by Brendan Eich, then working at Netscape and now of Mozilla. The original name of this language was Mocha, in September of 1995 it was changed to LiveScript, then in December of the same year, the name JavaScript was adopted, because of very popular Java around then.

CentOS 6/7 Multi-Boot Setup

Fri, 10 Jan 2014 14:59:31 +1100

Bootable usb preparation#

Download dvd iso from url or torrent Use Win32 Image Writer to create usb. ( Bootice is useful tool to reformat the USB as origin )

Install CentOS on virtual machine#

Before you install, you are better to backup anything on the device which you are going to install, and chcek your internet is working properly.
CentOS provide a friendly and nice installation process. If you choose VMWare or VirtulBox as machine, you can open installation steps on your browser or use ipad /tablet to access this page. You just need to follow the instruction step by step, it will be done within an hour or more(it varies in computing power of PC).

Generic Predicate & Expression

Mon, 01 Jan 0001 00:00:00 +0000

Generic Predicate and Expression for query#

Prerequisites#

You have experience of developing .net application, which includes entity framework.

You have experience of using SQL to query database

Problem#

Now entity framework is core component in all .net applications, which need to communicate with database.

Business service get a lot of benefits form entity framework’s ORM feature, and we can create a repository layer on the top of ORM to reduce some simple but tedious database operation, such as, delete, insert, query all data. However, when we need to do some complicated query to support business service, we still need to take so much effort to achieve the query result, because entity framework use LINQ as query language, comparing with SQL, native database language, it is a bit more complicated and cumbersome. Luckily, entity framework provide another generic feature to help us DRY. Predicate and expression can help us create generic query and reduce many reduntant code.

Adv Bash - 1

Mon, 01 Jan 0001 00:00:00 +0000

Special Characters#

What makes a character special? If it has a meaning beyond its literal meaning, a meta-meaning, then we refer to it as a special character. Along with commands and keywords, special characters are building blocks of Bash scripts.

Special Shell Variables#

Variable	Meaning
$0	Filename of script
$1	Positional parameter #1
$2 - $9	Positional parameters #2 - #9
${10}	Positional parameter #10
$#	Number of positional parameters
“$*”	All the positional parameters (as a single word) *
“$@”	All the positional parameters (as separate strings)
${#*}	Number of positional parameters
${#@}	Number of positional parameters
$?	Return value
$$	Process ID (PID) of script
$-	Flags passed to script (using set)
$_	Last argument of previous command
$!	Process ID (PID) of last job run in background

Operator Precedence#

In a script, operations execute in order of precedence: the higher precedence operations execute before the lower precedence ones.

Adv Bash - 2

Mon, 01 Jan 0001 00:00:00 +0000

Manipulating Strings#

Bash supports a surprising number of string manipulation operations. Unfortunately, these tools lack a unified focus. Some are a subset of parameter substitution, and others fall under the functionality of the UNIX expr command. This results in inconsistent command syntax and overlap of functionality, not to mention confusion.

String Operations#

Expression	Meaning
${#string}	Length of $string
${string:position}	Extract substring from $string at $position
${string:position:length}	Extract $length characters substring from $string at $position [zero-indexed,
${string#substring}	Strip shortest match of $substring from front of $string
${string##substring}	Strip longest match of $substring from front of $string
${string%substring}	Strip shortest match of $substring from back of $string
${string%%substring}	Strip longest match of $substring from back of $string
${string/substring/replacement}	Replace first match of $substring with $replacement
${string//substring/replacement}	Replace all matches of $substring with $replacement
${string/#substring/replacement}	If $substring matches front end of $string, substitute $replacement for $substring
${string/%substring/replacement}	If $substring matches back end of $string, substitute $replacement for $substring
expr match “$string” ‘$substring’	Length of matching $substring* at beginning of $string
expr “$string” : ‘$substring’	Length of matching $substring* at beginning of $string
expr index “$string” $substring	Numerical position in $string of first character in $substring* that matches [0 if no match, first character counts as position 1]
expr substr $string $position $length	Extract$length characters from $string starting at $position [0 if
expr match “$string” ‘($substring)’	Extract$substring*, searching from beginning of $string
expr “$string” : ‘($substring)’	Extract$substring* , searching from beginning of $string
expr match “$string” ‘.*($substring)’	Extract$substring*, searching from end of $string
expr “$string” : ‘.*($substring)’	Extract$substring*, searching from end of $string

Parameter Substitution and Expansion#

Expression	Meaning
${var}	Value of var (same as $var)
${var-$DEFAULT}	If var not set, evaluate expression as $DEFAULT *
${var:-$DEFAULT}	If var not set or is empty, evaluate expression as $DEFAULT *
${var=$DEFAULT}	If var not set, evaluate expression as $DEFAULT *
${var:=$DEFAULT}	If var not set or is empty, evaluate expression as $DEFAULT *
${var+$OTHER}	If var set, evaluate expression as $OTHER, otherwise as null string
${var:+$OTHER}	If var set, evaluate expression as $OTHER, otherwise as null string
${var?$ERR_MSG}	If var not set, print $ERR_MSG and abort script with an exit status of 1.*
${var:?$ERR_MSG}	If var not set, print $ERR_MSG and abort script with an exit status of 1.*
${!varprefix*}	Matches all previously declared variables beginning with varprefix
${!varprefix@}	Matches all previously declared variables beginning with varprefix

Samples#

Replace file name from abc_noteN to abc_N

touch abc_note1 abc_note2 abc_note3

for f in $(find . -type f -name *abc_note*); 
do 
 mv -- $f "${f//note}" 
done ;

ls abc*
# expected output
# abc_1 abc_2 abc_3

Adv Bash - 3

Mon, 01 Jan 0001 00:00:00 +0000

Operators: Files#

Operator	Tests Whether	Operator	Tests Whether
-e	File exists	-s	File is not zero size
-f	File is a regular file
-d	File is a directory	-r	File has read permission
-h	File is a symbolic link	-w	File has write permission
-L	File is a symbolic link	-x	File has execute permission
-b	File is a block device
-c	File is a character device	-g	sgid flag set
-p	File is a pipe	-u	suid flag set
-S	File is a socket	-k	“sticky bit” set
-t	File is associated with a terminal
-N	File modified since it was last read	F1 -nt F2	File F1 is newer than F2 *
-O	You own the file	F1 -ot F2	File F1 is older than F2 *
-G	Group id of file same as yours	F1 -ef F2	Files F1 and F2 are hard links to the same file *
!	NOT (inverts sense of above tests)

Sample#


function is_symbolic_link(){
 echo "Is the file $1 a symbolic link?";

 if [ -f $1 ] && [ -h $1 ]; 
 then
 echo 'true' ; 
 else 
 echo 'false'; 
 fi;
}

function is_file_empty () {

 echo "Is the file $1 empty?";

 if [ -f $1 ] && [ ! -s $1 ]; 
 then
 echo 'true' ; 
 else 
 echo 'false'; 
 fi;
}

C Lecture - 1

Mon, 01 Jan 0001 00:00:00 +0000

Author: Zed A. Shaw

All content comes from Zed’s Lecture Repository and Libraries Repository. All credit goes to Zed.

Exercise 0 Installing Software#

The Plan

Install software on your system.
Test that it works right.

Linux Install

On Debian/Ubuntu use:

$ sudo apt-get install build-essential

On RedHat/CentOS:

$ sudo yum groupinstall development-tools

Linux Testing

Test that your C compiler works with:

$ cc --version

OSX Install

Install XCode, this will take a while.

C Lecture - 2

Mon, 01 Jan 0001 00:00:00 +0000

Author: Zed A. Shaw

All content comes from Zed’s Lecture Repository and Libraries Repository. All credit goes to Zed.

Exercise 32 Double Linked Lists#

The Plan

Learn about your very first data structure:

Double Linked Lists

Creating A liblcthw Project

We’ll need a project for the rest of the book called liblcthw.

Algorithms and Data Structures

A big step in going from amateur to professional is learning about data structures and algorithms.

C Lecture - 3

Mon, 01 Jan 0001 00:00:00 +0000

Author: Zed A. Shaw

All content comes from Zed’s Lecture Repository and Libraries Repository. All credit goes to Zed.

Exercise 41 Project devpkg#

.\ex41\devpkg

.\ex41\devpkg\commands.c

#include <apr_uri.h>
#include <apr_fnmatch.h>
#include <unistd.h>

#include "commands.h"
#include "dbg.h"
#include "bstrlib.h"
#include "db.h"
#include "shell.h"

int Command_depends(apr_pool_t * p, const char *path)
{
 FILE *in = NULL;
 bstring line = NULL;

 in = fopen(path, "r");
 check(in != NULL, "Failed to open downloaded depends: %s", path);

 for (line = bgets((bNgetc) fgetc, in, '\n');
 line != NULL; 
 line = bgets((bNgetc) fgetc, in, '\n')) 
 {
 btrimws(line);
 log_info("Processing depends: %s", bdata(line));
 int rc = Command_install(p, bdata(line), NULL, NULL, NULL);
 check(rc == 0, "Failed to install: %s", bdata(line));
 bdestroy(line);
 }

 fclose(in);
 return 0;

error:
 if (line) bdestroy(line);
 if (in) fclose(in);
 return -1;
}

int Command_fetch(apr_pool_t * p, const char *url, int fetch_only)
{
 apr_uri_t info = {.port = 0 };
 int rc = 0;
 const char *depends_file = NULL;
 apr_status_t rv = apr_uri_parse(p, url, &info);

 check(rv == APR_SUCCESS, "Failed to parse URL: %s", url);

 if (apr_fnmatch(GIT_PAT, info.path, 0) == APR_SUCCESS) {
 rc = Shell_exec(GIT_SH, "URL", url, NULL);
 check(rc == 0, "git failed.");
 } else if (apr_fnmatch(DEPEND_PAT, info.path, 0) == APR_SUCCESS) {
 check(!fetch_only, "No point in fetching a DEPENDS file.");

 if (info.scheme) {
 depends_file = DEPENDS_PATH;
 rc = Shell_exec(CURL_SH, "URL", url, "TARGET", depends_file,
 NULL);
 check(rc == 0, "Curl failed.");
 } else {
 depends_file = info.path;
 }

 // recursively process the devpkg list
 log_info("Building according to DEPENDS: %s", url);
 rv = Command_depends(p, depends_file);
 check(rv == 0, "Failed to process the DEPENDS: %s", url);

 // this indicates that nothing needs to be done
 return 0;

 } else if (apr_fnmatch(TAR_GZ_PAT, info.path, 0) == APR_SUCCESS) {
 if (info.scheme) {
 rc = Shell_exec(CURL_SH,
 "URL", url, "TARGET", TAR_GZ_SRC, NULL);
 check(rc == 0, "Failed to curl source: %s", url);
 }

 rv = apr_dir_make_recursive(BUILD_DIR,
 APR_UREAD | APR_UWRITE |
 APR_UEXECUTE, p);
 check(rv == APR_SUCCESS, "Failed to make directory %s",
 BUILD_DIR);

 rc = Shell_exec(TAR_SH, "FILE", TAR_GZ_SRC, NULL);
 check(rc == 0, "Failed to untar %s", TAR_GZ_SRC);
 } else if (apr_fnmatch(TAR_BZ2_PAT, info.path, 0) == APR_SUCCESS) {
 if (info.scheme) {
 rc = Shell_exec(CURL_SH, "URL", url, "TARGET", TAR_BZ2_SRC,
 NULL);
 check(rc == 0, "Curl failed.");
 }

 apr_status_t rc = apr_dir_make_recursive(BUILD_DIR,
 APR_UREAD | APR_UWRITE
 | APR_UEXECUTE, p);

 check(rc == 0, "Failed to make directory %s", BUILD_DIR);
 rc = Shell_exec(TAR_SH, "FILE", TAR_BZ2_SRC, NULL);
 check(rc == 0, "Failed to untar %s", TAR_BZ2_SRC);
 } else {
 sentinel("Don't now how to handle %s", url);
 }

 // indicates that an install needs to actually run
 return 1;
error:
 return -1;
}

int Command_build(apr_pool_t * p, const char *url,
 const char *configure_opts, const char *make_opts,
 const char *install_opts)
{
 int rc = 0;

 check(access(BUILD_DIR, X_OK | R_OK | W_OK) == 0,
 "Build directory doesn't exist: %s", BUILD_DIR);

 // actually do an install
 if (access(CONFIG_SCRIPT, X_OK) == 0) {
 log_info("Has a configure script, running it.");
 rc = Shell_exec(CONFIGURE_SH, "OPTS", configure_opts, NULL);
 check(rc == 0, "Failed to configure.");
 }

 rc = Shell_exec(MAKE_SH, "OPTS", make_opts, NULL);
 check(rc == 0, "Failed to build.");

 rc = Shell_exec(INSTALL_SH,
 "TARGET", install_opts ? install_opts : "install",
 NULL);
 check(rc == 0, "Failed to install.");

 rc = Shell_exec(CLEANUP_SH, NULL);
 check(rc == 0, "Failed to cleanup after build.");

 rc = DB_update(url);
 check(rc == 0, "Failed to add this package to the database.");

 return 0;

error:
 return -1;
}

int Command_install(apr_pool_t * p, const char *url,
 const char *configure_opts, const char *make_opts,
 const char *install_opts)
{
 int rc = 0;
 check(Shell_exec(CLEANUP_SH, NULL) == 0,
 "Failed to cleanup before building.");

 rc = DB_find(url);
 check(rc != -1, "Error checking the install database.");

 if (rc == 1) {
 log_info("Package %s already installed.", url);
 return 0;
 }

 rc = Command_fetch(p, url, 0);

 if (rc == 1) {
 rc = Command_build(p, url, configure_opts, make_opts,
 install_opts);
 check(rc == 0, "Failed to build: %s", url);
 } else if (rc == 0) {
 // no install needed
 log_info("Depends successfully installed: %s", url);
 } else {
 // had an error
 sentinel("Install failed: %s", url);
 }

 Shell_exec(CLEANUP_SH, NULL);
 return 0;

error:
 Shell_exec(CLEANUP_SH, NULL);
 return -1;
}

.\ex41\devpkg\commands.h

C Lecture - 4

Mon, 01 Jan 0001 00:00:00 +0000

Author: Zed A. Shaw

All content comes from Zed’s Lecture Repository and Libraries Repository. All credit goes to Zed.

Exercise 48a A Simple Network Server:#

Project Description

The Plan

Start your first long running project:

statserve

The Purpose

You’ll get the project started and get a minimum first hack going.

The Requirements

Create a simple network server that accepts a connection on port 7899 from netclient or the nc command, and echoes back anything you type.
You’ll need to learn how to bind a port, listen on the socket, and answer it. Use your research skills to study how this is done and attempt to implement it yourself.

The Requirements

Cassandra Practices

Mon, 01 Jan 0001 00:00:00 +0000

Apache Cassandra is a free open-source database system that is NoSQL based. Meaning Cassandra does not use the table model seen in MySQL, MSSQL or PostgreSQL, but instead uses a cluster model. It’s designed to handle large amounts of data and is highly scalable.

Install Cassandra on Ubuntu#

Install Java(JRE) 8+#

sudo add-apt-repository ppa:webupd8team/java
sudo apt update
sudo apt-get install oracle-java8-set-default
java -version

Install Python 2.7+#

sudo apt install python
python --version

Install Cassandra#

First, we have to add Cassandra repository to source list by running following command. The 39x is the version. Use 40x if Cassandra 4.0 is the newest version:

echo "deb http://www.apache.org/dist/cassandra/debian 39x main" | \
sudo tee -a /etc/apt/sources.list.d/cassandra.sources.list

Next, run the cURL command to add the repository keys :

curl https://www.apache.org/dist/cassandra/KEYS | \
sudo apt-key add -

We can now update the repositories and install Cassandra:

sudo apt-get update
sudo apt install cassandra
# optional - It works on MacBook
sudo reboot

Check Cassandra status

nodetool status

Install Cassandra with Docker#

Create node n1#

docker run --name n1 -d tobert/cassandra -dc DC1 -rack RAC1
docker ps

Get IP of node n1#

IP=`docker inspect -f '{{ .NetworkSettings.IPAddress }}' n1`
echo $IP

Check status of n1#

docker exec -it n1 nodetool status

# You will see status of Datacenter D1 below

# Datacenter: DC1
# ===============
# Status=Up/Down
# |/ State=Normal/Leaving/Joining/Moving
# -- Address Load Tokens Owns (effective) Host ID Rack
UN 172.17.0.2 51.53 KB 256 100.0% 8965869d-cae8-41a6-bf19-ff69c2605c6c RAC1

Create node n2 on rack RAC2#

docker run --name=n2 -d tobert/cassandra -dc DC1 -rack RAC2 --seeds $IP

docker exec -it n1 nodetool status

# You will see status of Datacenter D1 below

# Datacenter: DC1
# ===============
# Status=Up/Down
# |/ State=Normal/Leaving/Joining/Moving
# -- Address Load Tokens Owns (effective) Host ID Rack
# UN 172.17.0.3 72.01 KB 256 100.0% cfa002b0-350c-41b8-9f86-eb8978a43b26 RAC2
# UN 172.17.0.2 51.53 KB 256 100.0% 8965869d-cae8-41a6-bf19-ff69c2605c6c RAC1

Check node n2 configuration#

docker exec -it n2 cat /data/conf/cassandra.yaml | grep endpoint
docker exec -it n2 cat /data/conf/cassandra-rackdc.properties | grep -e "dc" -e "rack"

Create node n3 on Datacenter D2 and rack RAC1#

docker run --name=n3 -d tobert/cassandra -dc DC2 -rack RAC1 --seeds $IP
docker exec -it n1 nodetool status

# You will see status below. It may take a few seconds to get everything up and run.

# Datacenter: DC1
# ===============
# Status=Up/Down
# |/ State=Normal/Leaving/Joining/Moving
# -- Address Load Tokens Owns (effective) Host ID Rack
# UN 172.17.0.3 134.03 KB 256 66.1% cfa002b0-350c-41b8-9f86-eb8978a43b26 RAC2
# UN 172.17.0.2 102.84 KB 256 64.5% 8965869d-cae8-41a6-bf19-ff69c2605c6c RAC1

# Datacenter: DC2
# ===============
# Status=Up/Down
# |/ State=Normal/Leaving/Joining/Moving
# -- Address Load Tokens Owns (effective) Host ID Rack
UN 172.17.0.4 14.38 KB 256 69.4% 0fad8335-763d-42fa-9934-3ed10c44eaa8 RAC1

Setup replication strategy#

docker 
create keyspace csdb with replication = {'class':'NetworkTopologyStrategy','DC1':2,'DC2':1}

Check csdb status#

docker exec -it n1 nodetool describering csdb

# Run nodetool status and note that the one node in DC2 owns all the data
docker exec -it n1 nodetool status csdb 

# Stop and remove all four docker containers:
docker stop n1 n2 n3 n4; docker rm n1 n2 n3 n4

Create single Datacenter with 3 nodes#

Create 3 nodes with local mounted directory#

docker run --name=n1 -v $PWD/ws/ps/cassdev/scripts:/scripts -d tobert/cassandra
docker exec -it n1 nodetool status

IP=`docker inspect -f '{{ .NetworkSettings.IPAddress }}' n1`
echo $IP

docker run --name=n2 -d tobert/cassandra --seeds $IP
docker run --name=n3 -d tobert/cassandra --seeds $IP

docker exec -it n1 /bin/bash
cd scripts

List scripts#

docker exec -it n1 /bin/bash
cd /scrpts && ls

Create keyspace with simple replication#

docker exec -it n1 cqlsh
create keyspace csdb with replication = 
{'class':'SimpleStrategy', 'replication_factor':1};

Create table and insert data with script#

docker exec -it n1 cqlsh

> desc keyspaces;
> desc tables;
> use ussdb;
> source '/scripts/courses.cql'
> source '/scripts/users.cql'

CQL#

docker exec -it n1 cqlsh

> use ussdb;
> desc tables;
> select * from users;
> select * from courses;

Troubleshoot#

Connection error

Cron Job Note - 1

Mon, 01 Jan 0001 00:00:00 +0000

Introduction#

Cron job is one of most common techniques used on every Unix / Linux.

Common Use Cases#

House keeping - Clean up the backup#

Run every night to remove the daily backup tar ball
Assumption:
- The script file named housekeeping.sh.
- The script sits inside folder bin which is under your user account.
- All backup files have the .tar as extension.
- The script will check the backup tar balls within the folder bacup, which is under your user account as well.
- The script will remove the latest backup if total backup files are over 5.
Cron Job setting -

Cron Job Note - 2

Mon, 01 Jan 0001 00:00:00 +0000

Refresh the database (NoSQL) - Cassandra#

The sample script is used to backup the data from production database and refresh the data to staging or test database. It is not supposed to restore data because of database corruption.

Backup the Cassandra database nightly#

There is a keyspace named hho_ks in the Cassandra nodes store the production data.
Every night the staging Cassandra server will be refreshed with production’s snapshot

Debug PHP with Free IDE

Mon, 01 Jan 0001 00:00:00 +0000

PDT and Netbeans#

PDT and Netbeans are two most popluar free PHP IDEs. We choose such IDE for productivity, so code intelligence and debug are two key factors, which let us love IDE. Because both are not created for PHP development at the start, there is no built-in server to support the PHP web debug. When we want to use it to debug, we would come across some wierd problems. Here is how to prepare the IDE for PHP debug.

Docker Practices

Mon, 01 Jan 0001 00:00:00 +0000

Docker is an open platform for developing, shipping, and running applications. Docker provides the ability to package and run an application in a loosely isolated environment called a container. The isolation and security allow you to run many containers simultaneously on a given host. Containers are lightweight because they don’t need the extra load of a hypervisor, but run directly within the host machine’s kernel. This means you can run more containers on a given hardware combination than if you were using virtual machines. You can even run Docker containers within host machines that are actually virtual machines!

F# Namespace, Module & Import

Mon, 01 Jan 0001 00:00:00 +0000

Namespace#

A namespace lets you organize code into areas of related functionality by enabling you to attach a name to a grouping of F# program elements. Namespaces are typically top-level elements in F# files.

Namespaces cannot directly contain values and functions. Instead, values and functions must be included in modules, and modules are included in namespaces. Namespaces can contain types, modules.

namespace [rec] [parent-namespaces.]identifier

Modules#

A module is a grouping of F# code, such as values, types, and function values, in an F# program. Grouping code in modules helps keep related code together and helps avoid name conflicts in your program.

Java Note - 1: Enum

Mon, 01 Jan 0001 00:00:00 +0000

Prerequisites#

Java 1.5+

New type: Enum#

Enum was a great improvement in Java 1.5. From that more and more developer abandom the interface or abstract class as constant variable container.

Before Java 5#

Before Java 1.5 you will following coding in many Java program.

 // Use interface or abstract class as constant variable container
 public interface Country {
 public static final String AU = "Australian";
 public static final String UK = "United Kingdom"; 
 public static final String US = "United State"; 
 }
 
 public class Util {
 
 public static String getLanguageCode(String country) {
 
 String languageCode = "en";
 switch (country) {
 case Country.AU:
 languageCode = "en-au";
 break;
 case Country.UK:
 languageCode = "en-uk";
 break;
 case Country.US:
 languageCode = "en-us";
 break;
 }
 return languageCode;
 }
 }

Above program looks very good. Please take a close look and check it carefully. You will find the program will never return en-au, since there is a typo in the constant AU. It should be Australia instead of Australian. I believe many developers have short sight problem like me, and it happened again and again. Using string as constant flag is not a good option, but there is no other better solution before Java 1.5.

Java Note - 2: Concurrency

Mon, 01 Jan 0001 00:00:00 +0000

Thread#

Join#

The join method allows one thread to wait for the completion of another. join responds to an interrupt by exiting with an InterruptedException.
Demo code of thread join

public class JoinDemo implements Runnable {
 private Random rand = new Random(System.currentTimeMillis());

 public void run() {
 //simulate some CPU expensive task
 for (int i = 0; i < 100000000; i++) {
 rand.nextInt();
 }
 System.out.println("[" + Thread.currentThread().getName() + "] finished .");
 }

 public static void main(String[] args) throws InterruptedException {
 Thread[] threads = new Thread[5];
 for (int i = 0; i < threads.length; i++) {
 threads[i] = new Thread(new JoinDemo(), "joinThread " + i);
 threads[i].start();
 }
 for (int i = 0; i < threads.length; i++) {
 threads[i].join();
 }
 System.out.println("[" 
 + Thread.currentThread().getName() 
 + "] All -threads have finished.");
 }
}

Common problem of multithred program#

When there are many threads running, the exact sequence in which all running threads are executed depends next to the thread configuration like priority also on the available CPU resources and the way the scheduler chooses the next thread to execute. Although the behavior of the scheduler is completely deterministic, it is hard to predict which threads execute in which moment at a given point in time. This makes access to shared resources critical as it is hard to predict which thread will be the first thread that tries to access it.

Java Note - 3: Path and Files

Mon, 01 Jan 0001 00:00:00 +0000

Prerequisites#

Java 7+

Good stuff from not shiny Java 7#

If you are planning to refactor your code, please give a second thought. It is time to dump to try these new features. When the Java 7 was released, I was kind of disappointed without lambda, jigsaw as most developers, but when I tried new Path, Files API, I found that is great improvement. The enhancement of this new IO is really useful. It save so much effort for Java developer.

Java Note - 4: Date Time

Mon, 01 Jan 0001 00:00:00 +0000

Date-Time API#

Through the java.time packages, Java 8 provides a comprehensive Date-Time API to work with date, time, and datetime. By default, most of the classes are based on the ISO-8601 standards. The main classes are

Instant
- represents an instant on the timeline and it is suitable for machines, for example, as timestamps for event
LocalDate, LocalTime, LocalDateTime
- represents human readable date, time, and datetime without a time zone.
OffsetTime, OffsetDateTime

Java Note - 5: Lambda

Mon, 01 Jan 0001 00:00:00 +0000

Lamda#

Lambda Best Practices#

Use Interfaces#

The most common misstep taken by an over-eager functional programmer is the use of functional interfaces in type signatures. In general, you should avoid using the functional interface types directly and instead provide single-method interfaces as arguments to your methods. These interfaces become a way to create self-documenting code and to provide meaningful type information, as well as leaving open the opportunity for your user to provide an actual Java type.

Java Note - 7: Stream API

Mon, 01 Jan 0001 00:00:00 +0000

Stream#

Iterations#

Collections and Maps#

Filtering#

Mapping#

LambdaCollectionDemo#

Lambda Collection Map Demo#



public class LambdaCollectionMapDemo {

 public static void main(String[] args) {

 // FunctionalInterface 
 System.out.println("x + y:" + engine((x, y) -> x + y));// w w w .j av a 2s. c om
 System.out.println("x - y:" + engine((x, y) -> x * y));
 System.out.println("x * y:" + engine((x, y) -> x / y));
 System.out.println("x / y:" + engine((x, y) -> x % y));

 String[] strArray = new String[] { "abc", "klm", "xyz", "pqr" };
 List list = Arrays.asList(strArray);

 // Default Methods
 list.forEach(System.out::println);

 Arrays.sort(strArray, (first, second) -> first.compareToIgnoreCase(second));
 list = Arrays.asList(strArray);

 System.out.println("After sorting ... ");
 list.forEach(System.out::println);



 // Common Functional Interfaces
 // Runnable
 repeat(5, () -> System.out.println("Hello")) ;

 // UnaryOperator
 UnaryOperator<String> upperCase = str -> str.toUpperCase();
 // BiUnaryOperator
 BinaryOperator<String> concat = (left,right) -> left + right;

 System.out.println( " UnaryOperator upperCase "+upperCase.apply( "hello") );
 System.out.println( " BinaryOperator<String> concat "+ concat.apply("hello","world"));
 

 }

 private static int engine(Calculator calculator) {
 int x = 2, y = 4;
 return calculator.calculate(x, y);
 }

 public static void repeat(int n, Runnable action) {
 for (int i = 0; i < n; i++)
 action.run();
 }
}

@FunctionalInterface
interface Calculator {
 int calculate(int x, int y);
}

Java Note - Part 6: Lambda & Collection

Mon, 01 Jan 0001 00:00:00 +0000

Lambda and Collection#

Iterations#

Collections and Maps#

Filtering#

Mapping#

LambdaCollectionDemo#

Lambda Collection Map Demo#

public class LambdaCollectionMapDemo {

 public static void main(String[] args) {

 // FunctionalInterface 
 System.out.println("x + y:" + engine((x, y) -> x + y));// w w w .j av a 2s. c om
 System.out.println("x - y:" + engine((x, y) -> x * y));
 System.out.println("x * y:" + engine((x, y) -> x / y));
 System.out.println("x / y:" + engine((x, y) -> x % y));

 String[] strArray = new String[] { "abc", "klm", "xyz", "pqr" };
 List list = Arrays.asList(strArray);

 // Default Methods
 list.forEach(System.out::println);

 Arrays.sort(strArray, (first, second) -> first.compareToIgnoreCase(second));
 list = Arrays.asList(strArray);

 System.out.println("After sorting ... ");
 list.forEach(System.out::println);



 // Common Functional Interfaces
 // Runnable
 repeat(5, () -> System.out.println("Hello")) ;

 // UnaryOperator
 UnaryOperator<String> upperCase = str -> str.toUpperCase();
 // BiUnaryOperator
 BinaryOperator<String> concat = (left,right) -> left + right;

 System.out.println( " UnaryOperator upperCase "+upperCase.apply( "hello") );
 System.out.println( " BinaryOperator<String> concat "+ concat.apply("hello","world"));
 

 }

 private static int engine(Calculator calculator) {
 int x = 2, y = 4;
 return calculator.calculate(x, y);
 }

 public static void repeat(int n, Runnable action) {
 for (int i = 0; i < n; i++)
 action.run();
 }
}

@FunctionalInterface
interface Calculator {
 int calculate(int x, int y);
}

JS & ES Note - 1

Mon, 01 Jan 0001 00:00:00 +0000

The most unpredictable keyword and feature#

You may already guessed what I am talking about. Yes, thethis keyword. It is not only a powerful feature, but also often misinterpreted keyword.

In JavaScript, we also have this concept inside a Function constructor when it is invoked using the “new” keyword, however it is not the only rule and “this” can often refer to a different object from a different execution context.

JS & ES Note - 2

Mon, 01 Jan 0001 00:00:00 +0000

The equal operator doesn’t always mean equivalent#

Have you got confused by the equal or not equal expression in the JavaScript? I will say you are definitely not the only one. Even many senior developers come from back-end programming background, they all scratch the head to find out why the equal or not-equal expression doesn’t work as they expect. The truth is those expression are really different from other programming language.

JS & ES Note - 3

Mon, 01 Jan 0001 00:00:00 +0000

The var statement#

var declarations, wherever they occur, are processed before any code is executed. This is called hoisting.
The scope of a variable declared with var is its current execution context, which is either the enclosing function or, for variables declared outside any function, global. If you re-declare a JavaScript variable, it will not lose its value.
Assigning a value to an undeclared variable implicitly creates it as a global variable (it becomes a property of the global object) when the assignment is executed.

JS & ES snippet

Mon, 01 Jan 0001 00:00:00 +0000

Setup the global node modules#

Add an environment variable to tell node where the global node module sits

# I use nvm to manage my node and node modules
export NODE_PATH=${HOME}/.nvm/versions/node/<node_version>/lib/node_modules

If you use npm by default, you may have permission problem to access the node modules. I suggest you to set a customized global node module folder under your home directory.
- Create a new folder under your home directory
- Install npm to new global node module
- update environment variables in the profile
```
mkdir $HOME/.node_modules
npm config set prefix $HOME/.node_modules
npm install -g npm
echo 'export NODE_MODULES=$HOME/.node_modules' >> $HOME/.profile
echo 'export PATH=$PATH:$NODE_MODULES/bin' >> $HOME/.profile
source $HOME/.profile
```

Parsing CSV file#

Parse csv file with fast-csv#

Install package fast-csv globally

Kubernetes Cluster in 5min

Mon, 01 Jan 0001 00:00:00 +0000

Kubernetes#

Kubernetes (K8s) is an open-source system for automating deployment, scaling, and management of containerized applications.

It groups containers that make up an application into logical units for easy management and discovery. Kubernetes builds upon 15 years of experience of running production workloads at Google, combined with best-of-breed ideas and practices from the community.

Purpose#

This project focuses on the training and demonstration. Please DO NOT use it in production environment.

MySql: DDL & DML

Mon, 01 Jan 0001 00:00:00 +0000

As one of most popular open source databases, MySql is mainly used as data storage, aka database. To store the data into MySql server, we need to use SQL - Structural Query Language. But before we store the data to MySql, we need to define the schema which tells MySql how to organize the data in the proper manner. To define the schema, there is a special set of SQL, which we call it DDL - Data Definition Language, such as, CREATE, DROP, ALTER, etc.

MySql: Getting Started

Mon, 01 Jan 0001 00:00:00 +0000

MySQL is the world’s most popular open source database. Whether you are a fast growing web property, technology ISV or large enterprise, MySQL can cost-effectively help you deliver high performance, scalable database applications.

Prerequisite#

Install MySql 5.6+ on your PC or server

Launch & Stop MySql server#

# use systemctl
systemctl status mysql.service
systemctl restart mysql.service

# use service
service mysql status
service mysql restart

Set root password#

mysql_secure_installation

Reset root password#

-- MySql 5.6.x
mysql> UPDATE mysql.user SET password = PASSWORD('YourNewPassword') 
 -> WHERE User = 'root' AND Host = 'localhost';

-- MySql 5.7+
mysql> UPDATE mysql.user SET authentication_string = PASSWORD('YourNewPassword') 
 -> WHERE User = 'root' AND Host = 'localhost'; 

mysql> FLUSH PRIVILEGES;

Connect to MySql server#

mysql -u <user_name> -p -P <port> -h <host_name>

Add a new user#

CREATE USER 'user1'@'%' IDENTIFIED BY 'pass1';
GRANT ALL PRIVILEGES ON * . * TO 'user1'@'%';

Delete a user#

REVOKE ALL PRIVILEGES, GRANT OPTION FROM 'user1'@'%';
DROP USER 'user1'@'%';

MySql: JSON

Mon, 01 Jan 0001 00:00:00 +0000

Json support#

As of MySQL 5.7.8, MySQL supports a native JSON data type defined by RFC 7159 that enables efficient access to data in JSON (JavaScript Object Notation) documents. The JSON data type provides these advantages over storing JSON-format strings in a string column:

Automatic validation of JSON documents stored in JSON columns. Invalid documents produce an error.
Optimized storage format. JSON documents stored in JSON columns are converted to an internal format that permits quick read access to document elements. When the server later must read a JSON value stored in this binary format, the value need not be parsed from a text representation. The binary format is structured to enable the server to look up subobjects or nested values directly by key or array index without reading all values before or after them in the document.

MySql: Schema & Metadata

Mon, 01 Jan 0001 00:00:00 +0000

Information schema#

INFORMATION_SCHEMA provides access to database metadata, information about the MySQL server such as the name of a database or table, the data type of a column, or access privileges. Other terms that are sometimes used for this information are data dictionary and system catalog.

Check out table size#

SET @target_schema='THE_TARGET_SCHEMA';

SELECT 
 TABLE_NAME, table_rows, data_length, index_length, 
 round(((data_length + index_length) / 1024 / 1024 /1024),2) 'Size in GB',
 round(((data_length + index_length) / 1024 / 1024 ),2) 'Size in MB' 
FROM information_schema.TABLES
WHERE table_schema = @target_schema
ORDER BY data_length DESC
LIMIT 50;

Check out running process#

SET @target_schema='THE_TARGET_SCHEMA';

SELECT * FROM information_schema.PROCESSES
WHERE command <> 'Sleep'
 AND db = target_schema 

;

-- Another short cut to show all process

SHOW FULL PROCESSLIST;

Get the information of stored proc or function#

SET @target_schema='THE_TARGET_SCHEMA';

SELECT * FROM information_schema.ROUTINES
WHERE routine_schema = target_schema 
;

Optimize table after deletion#

-- Query the table sorted by data free space
SELECT table_name , data_length, data_free
FROM information_schema.tables
WHERE table_schema=@target_schema 
AND data_free > 0
ORDER BY data_free DESC


-- Get table names which need optimization
SELECT table_name
FROM information_schema.tables
WHERE table_schema=@target_schema 
AND data_free > 0
ORDER BY data_free DESC


-- Optmize table 
OPTIMIZE TABLE XXXXX

MySql: SP & Func

Mon, 01 Jan 0001 00:00:00 +0000

Function - UDF#

For the UDF mechanism to work, functions must be written in C or C++ and your operating system must support dynamic loading. MySQL source distributions include a file sql/udf_example.cc that defines five UDF functions. Consult this file to see how UDF calling conventions work. The include/mysql_com.h header file defines UDF-related symbols and data structures, although you need not include this header file directly; it is included by mysql.h.

NeoVim

Mon, 01 Jan 0001 00:00:00 +0000

This article will show you how to empower your vi with NeoVim.

NeoVim#

Neovim is a refactor, and sometimes redactor, in the tradition of Vim (which itself derives from Stevie). It is not a rewrite but a continuation and extension of Vim. Many clones and derivatives exist, some very clever—but none are Vim. Neovim is built for users who want the good parts of Vim, and more.

Install Neovim#

Please follow the installation instructions here

PostgresQL Note - 1

Mon, 01 Jan 0001 00:00:00 +0000

PostgreSQL is a powerful, open source object-relational database system with over 30 years of active development that has earned it a strong reputation for reliability, feature robustness, and performance.

Getting Started#

Switch to user postges

sudo su - postgres

psql

Create new login id as super admin

It is frequently convenient to group users together to ease management of privileges: that way, privileges can be granted to, or revoked from, a group as a whole. In PostgreSQL this is done by creating a role that represents the group, and then granting membership in the group role to individual user roles.

PowerShell 7

Mon, 01 Jan 0001 00:00:00 +0000

This article will show you how to empower your Windows OS with modern PowerShell & other convenient tools.

PowerShell#

PowerShell is a cross-platform task automation solution made up of a command-line shell, a scripting language, and a configuration management framework. PowerShell runs on Windows, Linux, and macOS.

PowerShell 7#

Differences between PS 5 and PS 7#

Windows PowerShell 5.1 is built on top of the .NET Framework v4.5. With the release of PowerShell 6.0, PowerShell became an open source project built on .NET Core 2.0. PowerShell 7.0 is built on .NET Core 3.1. And, with the release of PowerShell 7.2, PowerShell will be built on .NET 6.0. Moving from the .NET Framework to .NET Core allowed PowerShell to become a cross-platform solution. PowerShell runs on Windows, macOS, and Linux.

Powershell Note - 1

Mon, 01 Jan 0001 00:00:00 +0000

PowerShell is a task-based command-line shell and scripting language built on .NET. PowerShell helps system administrators and power-users rapidly automate tasks that manage operating systems (Linux, macOS, and Windows) and processes.

Prerequisites#

The OS of Windows 7 or later version
Install Powershell 4 or later version. You can find it on Microsoft website
Has basic computer knowledge

Launch PS command prompt#

Type command on windows command prompt: powershell

Get PS Version#

Type $psversiontable

 PS C:\>$psversiontable
 ## You might see sth below

 Name Value
 ---- -----
 PSVersion 4.0
 WSManStackVersion 3.0
 SerializationVersion 1.1.0.1
 CLRVersion 4.0.30319.42000
 BuildVersion 6.3.9600.18773
 PSCompatibleVersions {1.0, 2.0, 3.0, 4.0}
 PSRemotingProtocolVersion 2.2

Install & Uninstall service#

# Install service
New-Service -Name "Your_Service_Name" -BinaryPathName "C:\path_to_your_service\your_service.exe -k netsvcs"

# Uninstall service 
(Get-WmiObject -Class Win32_Service -Filter "Name='Your_Service_Name'").delete()


$Username = 'domain\username'
$PassTxt = 'your secret'
$Password = ConvertTo-SecureString -AsPlainText $PassTxt -Force
 set-executionpolicy remotesigned; 
New-LocalUser $Username -Password $Password -FullName $Username -Description $Username
Add-LocalGroupMember -Group "Administrators" -Member $Username
Add-LocalGroupMember -Group "Remote Desktop Users" -Member $Username

Python Web Framework

Mon, 01 Jan 0001 00:00:00 +0000

Django is a high-level Python Web framework that encourages rapid development and clean, pragmatic design. Built by experienced developers, it takes care of much of the hassle of Web development, so you can focus on writing your app without needing to reinvent the wheel. It’s free and open source.

Install Python, pip and virtualenv#

Windows: Please find in from Home Page
Ubuntu: Please find it from Ubuntu setup
Python 3.4 (released March 2014) and Python 2.7.9 (released December 2014) ship with Pip.

Qemu & Virtual Machine

Mon, 01 Jan 0001 00:00:00 +0000

What is Qemu ?

QEMU is free and open source. And is licensed under GPL 2. it has the ability to run under both KVM and XEN models (if you enabled virtualization technology from your BIOS first) and offers a lot of options and virtualization options. In this article, we’ll explain how to use QEMU and install it.

QEMU is a virtualization technology emulator that allows you to run operating systems and Linux distributions easily on your current system without the need to install them or burn their ISO files. It is like VMware or VirtualBox. You can use it at anytime to emulate running any operating system you want on a lot of devices and architecture.

Scheduled task with window service

Mon, 01 Jan 0001 00:00:00 +0000

Problem#

Set up the some scheduled tasks running in the backgroud to take care of data update or sync for every 15 mins, or everyday or every week

Solution#

Option 1#

Windows Task Scheduler#

Click the Start button.
Click Control Panel.
Click System and Maintenance.
Click Administrative Tools.
Double-click Task Scheduler.

Option 2#

Use Window Service as task scheduler#

Overview of design#

The design here is a simplified version, which I built for previous projects. In the real world, I need to tailor it for different project with different purpose, but fundamental design of architect is the same. IMO, the design below can support most cases, which needs scheduled backgroud task service.

Sql Server Note - 1

Mon, 01 Jan 0001 00:00:00 +0000

SQL Server#

Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which may run either on the same computer or on another computer across a network (including the Internet).

Get db/table size or space#

Get db size

-- Get database size 
SELECT sys.databases.name, 
 CONVERT(VARCHAR,SUM(size)*8/1024)+' MB' AS TotalDiskSpaceMB ,
 CONVERT(VARCHAR,SUM(size)*8/1024/1024)+' GB' AS TotalDiskSpaceGB
FROM sys.databases 
JOIN sys.master_files 
ON sys.databases.database_id=sys.master_files.database_id 

GROUP BY sys.databases.name 
ORDER BY TotalDiskSpaceMB

-- Get database space & unallocated space
exec sp_spaceused

--

Get table size

SELECT 
 t.NAME AS TableName,
 s.Name AS SchemaName,
 p.rows AS RowCounts,
 SUM(a.total_pages) * 8 AS TotalSpaceKB,
 CAST(ROUND(((SUM(a.total_pages) * 8) / 1024.00), 2) AS NUMERIC(36, 2))
 AS TotalSpaceMB,
 SUM(a.used_pages) * 8 AS UsedSpaceKB, 
 CAST(ROUND(((SUM(a.used_pages) * 8) / 1024.00), 2) AS NUMERIC(36, 2))
 AS UsedSpaceMB,
 (SUM(a.total_pages) - SUM(a.used_pages)) * 8 AS UnusedSpaceKB,
 CAST(ROUND(((SUM(a.total_pages) - SUM(a.used_pages)) * 8) / 1024.00, 2) AS NUMERIC(36, 2))
 AS UnusedSpaceMB

FROM sys.tables t
INNER JOIN sys.indexes i ON t.OBJECT_ID = i.object_id
INNER JOIN sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id
INNER JOIN sys.allocation_units a ON p.partition_id = a.container_id
LEFT OUTER JOIN sys.schemas s ON t.schema_id = s.schema_id

WHERE t.NAME NOT LIKE 'dt%' 
 AND t.is_ms_shipped = 0
 AND i.OBJECT_ID > 255 
GROUP BY t.Name, s.Name, p.Rows
ORDER BY t.Name;

Get full text search objects#

SELECT 
 SCHEMA_NAME(tbl.schema_id) as SchemaName,
 tbl.name AS TableName, 
 FT_ctlg.name AS FullTextCatalogName,
 i.name AS UniqueIndexName,
 scols.name AS IndexedColumnName
FROM 
 sys.tables tbl
INNER JOIN 
 sys.fulltext_indexes FT_idx 
ON 
 tbl.[object_id] = FT_idx.[object_id] 
INNER JOIN 
 sys.fulltext_index_columns FT_idx_cols
ON 
 FT_idx_cols.[object_id] = tbl.[object_id]
INNER JOIN
 sys.columns scols
ON 
 FT_idx_cols.column_id = scols.column_id
 AND FT_idx_cols.[object_id] = scols.[object_id]
INNER JOIN 
 sys.fulltext_catalogs FT_ctlg
ON 
 FT_idx.fulltext_catalog_id = FT_ctlg.fulltext_catalog_id
INNER JOIN 
 sys.indexes i
ON 
 FT_idx.unique_index_id = i.index_id
 AND FT_idx.[object_id] = i.[object_id];

Find the table#

Find table by naming pattern

SELECT distinct	t.name AS 'TableName'
FROM sys.columns c
JOIN sys.tables t ON c.object_id = t.object_id
WHERE t.name LIKE '%bk%'
ORDER BY TableName;

Find table by colume name

SELECT c.name AS 'ColumnName'
 ,t.name AS 'TableName'
FROM sys.columns c
JOIN sys.tables t ON c.object_id = t.object_id
WHERE c.name LIKE '%MyName%'
ORDER BY TableName
 ,ColumnName;

EXEC sp_change_users_login Report

EXEC sp_change_users_login 'Auto_Fix', 'your_username', NULL, 'your_password';

USE [master]
GO
CREATE LOGIN [sql_user_id] WITH PASSWORD=N'sql_login_pass', 
DEFAULT_DATABASE=[Your_Database], CHECK_EXPIRATION=OFF, CHECK_POLICY=OFF
GO

USE [Your_Database]
GO
CREATE USER [sql_user_id] FOR LOGIN [sql_user_id]
GO
ALTER USER [sql_user_id] WITH DEFAULT_SCHEMA=[sql_user_id]
GO
CREATE SCHEMA [sql_user_id] AUTHORIZATION [sql_user_id]
GO
ALTER ROLE [db_datareader] ADD MEMBER [sql_user_id]
GO
ALTER ROLE [db_datawriter] ADD MEMBER [sql_user_id]
GO

Get Connection Info#


EXEC sp_who
GO

EXEC sp_who @loginname='user_id'
GO

-- Enhanced verssion
EXEC sp_who2
GO

Thread & Task

Mon, 01 Jan 0001 00:00:00 +0000

C# Thread & Task#

From Net 4.0, .Net applicatoin introduced Parallel Framework Extensions (PFx), along the way it delivered an entirely new model for async processing in .NET. In .NET 4.0 the thread pool queue was redesigned with the new requirements of PFx in mind. Instead of using a simple linked list, the queue was built with arrays of work items with the arrays connected into a linked list.

TS: Basic Types

Mon, 01 Jan 0001 00:00:00 +0000

Basic Types#

In TypeScript, the same types as you would expect in JavaScript are supported, with a convenient enumeration type thrown in to help things along.

Types in JavaScript#

Boolean - The most basic datatype is the simple true/false value, aka boolean value.
```
 let isDone: boolean = false;
```

Number - All numbers in TypeScript are floating point values.

 let decimal: number = 6;
 let hex: number = 0xf00d;
 let binary: number = 0b1010;
 let octal: number = 0o744;

String - Another fundamental part of creating programs in JavaScript for webpages and servers alike is working with textual data. TypeScript also uses double quotes (") or single quotes (’) to surround string data.

VirtualBox Notes

Mon, 01 Jan 0001 00:00:00 +0000

Network#

Not attached.#

In this mode, Oracle VM VirtualBox reports to the guest that a network card is present, but that there is no connection. This is as if no Ethernet cable was plugged into the card. Using this mode, it is possible to “pull” the virtual Ethernet cable and disrupt the connection, which can be useful to inform a guest operating system that no network connection is available and enforce a reconfiguration.

Windows Terminal

Mon, 01 Jan 0001 00:00:00 +0000

Windows Terminal#

The Windows Terminal is a modern, fast, efficient, powerful, and productive terminal application for users of command-line tools and shells like Command Prompt, PowerShell, and WSL. Its main features include multiple tabs, panes, Unicode and UTF-8 character support, a GPU accelerated text rendering engine, and custom themes, styles, and configurations.

Prerequisite#

PowerShell 7
- Install latest PowerShell (version 7.x) from Windows Store
Scoop
- Scoop can be found here or simply execute the command below

Hello World

CMMI

CMMI#

CMMI model#

CMMI 2.0

CMMI 2.0#

Guilding Principles#

Key Improvements#

COBIT 5

COBIT 5#

Scrum VS Kanban

Scrum VS Kanban#

Agile#

AWS: IAM

IAM#

Root User#

Dos and Don’ts#

Features & Functions#

MFA#

IAM User#

Azure: CAF - 1

Cloud Adoption Framework#

Azure: CAF - 2

Function#

Team#

cloud strategy team#

Azure: CAF - 3

cloud adoption strategy#

Azure: RBAC - 1

RBAC#

What to do with RBAC#

How it works#

Azure: RBAC - 2

Roles#

History#

Azure: RBAC - 3

Best practices#

Only grant the access users need#

Data Types & Ownership

Mutability#

DigitialOcean: Droplet

Droplet#

Prerequisite#

OS Options#

Plans and Pricing#

F# Overview

F##

Organizing F# Code#

Literals and Strings#

Getting started

Go Introduction#

Package & Module

Package & Module#

sys.path#

AWS : CLI - 1

AWS CLI#

CLI installation (Version 1)#

Install Python 3#

Profile Setup#

AWS : CLI - 2

AWS CLI & VPC#

AWS : CLI - 3

AWS CLI & & Security Group#

Closure & Decorator

Closure & Decorator#

LEGB rules#

Local function#

Closure#

DigitialOcean: Get Started

User Setup#

Create a new admin user#

Add a new user#

Set SSH access for new user#

Login as new user via SSH#

Set root password & disable SSH#

Security Update#

Tagging & Cloud Firewall#

Other Features#

Floating IPs#

Map, Function & Closure

F`#`#