DEV Community: Vinoth Kumar

AWS - EC2 Instance purchasing options

Vinoth Kumar — Sun, 20 Sep 2020 10:52:09 +0000

Amazon EC2 provides purchasing options to enable you to optimize your costs based on your needs.

On-Demand Instances

Pay, by the second, for the instances that you launch.
No longer-term commitments or upfront payments are needed.
You have full control over its lifecycle, you decide when to launch, start, stop, reboot, or terminate it.
You pay only when your On-Demand Instances are in the running state.
Can increase or decrease your compute capacity.

Reserved Instances

Up to 75% savings compared to On-Demand Instance pricing.
You can purchase a Reserved Instance for a one-year or three-year commitment, with the three-year commitment offering a bigger discount.
Commitment includes instance type and Region.
Reserved Instances do not renew automatically; when they expire, you can continue using the EC2 instance without interruption, but you are charged On-Demand rates.
After you purchase a Reserved Instance, you cannot cancel your purchase. However, you may be able to modify, exchange, or sell your Reserved Instance if your needs change.

Scheduled Reserved Instances

Purchase instances that are always available on the specified recurring schedule.
Recur on a daily, weekly, or monthly basis, with a specified start time and duration.
You pay for the time that the instances are scheduled, even if you do not use them.
After you purchase a Scheduled Instance, you can't cancel, modify, or resell your purchase.
You must purchase a Scheduled Reserved Instance minimum for one year.
The minimum required utilization is 1,200 hours per year.

Spot Instances

The most cost-efficient instance in AWS. Up to 90% savings compared to On-Demand Instance pricing.
Request unused EC2 instances, which can reduce your Amazon EC2 costs significantly.
Instances that can "lose" at any point of time if your max price is less than the current spot price.
Well-suited for batch jobs, background processing, and optional tasks. Not good for critical jobs.

Dedicated Hosts

Pay for a physical host.
Physical server with EC2 instance capacity fully dedicated to your use.
Full control of the Instance placement.
Visibility into the underlying socket, the core of the hardware.
You must purchase a Dedicated Hosts Instance minimum for one year.

Dedicated Instances

Pay, by the hour, for instances that run on hardware that's dedicated to a single customer.
May share hardware with other instances from the same AWS account.

Great combo

Reserved Instance for baseline + On-Demand and Spot Instances for scaling.

Resource

Original post - https://blog.vnoit.com/ec2-instance-purchasing-options

Redis

Vinoth Kumar — Sat, 20 Jun 2020 10:48:49 +0000

What is Redis?

Redis is an open-source, in-memory data structure store used as database, cache and message broker
Redis, which stands for Remote Dictionary Server.
NoSQL Key/Value Store with some advance features.
The different between MongoDB and Redis is Mongo DB is a disk-based document store while Redis is a memory-based.
Redis does not support any built-in data encryption

Why Redis?

Redis is blazingly fast it's written in C, runs entirely in memory and is optimized to deliver millions of operations with sub-millisecond latency with a single standard server.
Pre-built data structures for popular use cases which are used by developer like LEGO building blocks when creating new apps.
These built-in data structures include lists, sets, sorted sets, hashes, hyperloglogs, bitmaps, geospatial indexes, bitfields, streams and strings.
Redis commands allow data to be processed on the database level rather than the application level, reducing coding effort, code complexity and bandwidth requirements.
Redis can be extended infinitely.
With Redis Modules that expand Redis infinitely, and it allows to add custom functionality and structures.
And Modules that do everything from search to machine learning, security, JSON to graph data processing and more.
Has client libraries for every language.
The hottest Redis uses includes real-time analytics, High-speed transactions, High-speed data ingest, Message queues, Session storage, In-app social functionality, application job management, Search, Machine learning and caching.
Redis has been benchmarked as the world's fastest database.

Data types in Redis

Lists
Sets
Sorted sets
Hashes
Hyperlogs
Bitmaps
Geospatial indexes
Bitfields
Streams
Strings

Installing Redis

Basic commands to install redis.

$ sudo apt update

$ sudo apt install redis-server

$ redis-server # start redis server

$ redis-cli # opens a redis prompt

Basic Redis CLI

SET
SETNX - SET if Not e*X*ists
GET
DEL
EXISTS
MSET - Multi SET
MSETNX - Multi SET if Not e*X*ists
MGET - Multi GET

Note : Other keywords are self-explanatory

SET

Set key to hold the string value.
If the key already holds a value, it is overwritten, regardless of its type.
Time complexity: O(1)

SET key value # Syntax


SET mykey "Hello" # Examples

SETNX

Set key to hold string value if the key does not exist.
In that case, it is equal to SET.
When key already holds a value, no operation is performed.
SETNX is short for "SET if Not e*X*ists".
Time complexity: O(1)

SETNX key value # Syntax


SETNX mykey "Hello" # Examples

GET

Get the value of the key.
If the key does not exist the special value nil is returned.
An error is returned if the value stored at key is not a string, because GET only handles string values.
Time complexity: O(1)

GET key # Syntax


GET mykey # Example

DEL

Removes the specified keys.
A key is ignored if it does not exist.
Time complexity: O(N) where N is the number of keys that will be removed.
Removing a single key that holds a string value is O(1).

DEL key [key ...] # Syntax


DEL key1 key2 key3 # Example

EXISTS

Returns 1 if key exists, 0 if the key does not exist.
Time complexity: O(1)

EXISTS key [key ...] # Syntax


EXISTS key1 key2 # Example

MSET

Sets the given keys to their respective values.
Replaces existing values with new values, just as regular SET.
Time complexity: O(N) where N is the number of keys to set.

MSET key value [key value ...] # Syntax


MSET key1 "Hello" key2 "World" # Example

MSETNX

Sets the given keys to their respective values.
Will not perform any operation at all even if just a single key already exists.
Time complexity: O(N) where N is the number of keys to set.

MSETNX key value [key value ...] # Syntax


MSETNX key1 "Hello" key2 "there" # Example

MGET

Returns the values of all specified keys.
For every key that does not hold a string value or does not exist, the special value nil is returned.
Time complexity: O(N) where N is the number of keys to retrieve.

MGET key [key ...] # Syntax


MGET key1 key2 # Example

Resource

Optional Chaining

Vinoth Kumar — Tue, 25 Feb 2020 18:41:52 +0000

An optional chain is a chain of one or more property accesses and function calls, the first of which begins with the token ?..

Long chains of property accesses in JavaScript can be error-prone, as any of them might evaluate to null or undefined (also known as “nullish” values).

Checking for property existence on each step easily turns into a deeply-nested structure of if-statements.

// Error prone-version, could throw.
const nameLength = db.user.name.length;

// Less error-prone, but harder to read.
let nameLength;
if (db && db.user && db.user.name) {
  nameLength = db.user.name.length;
}

Using the new optional chaining operator, we can rewrite the above example as follows:

// Still checks for errors and is much more readable.
const nameLength = db?.user?.name?.length;

The ?. operator functions similarly to the . chaining operator, except that instead of causing an error if a reference is nullish (null or undefined), the expression short-circuits with a return value of undefined.

When used with function calls, it returns undefined if the given function does not exist.

let result = someInterface.customMethod?.();

Note: If there is a property with such a name and which is not a function, using ?. will still raise a TypeError exception (x.y is not a function).

Optional callbacks or event handlers

// Written as of ES2019
function doSomething(onContent, onError) {
  try {
    // ... do something with the data
  } catch (err) {
    if (onError) {
      // Testing if onError really exists
      onError(err.message);
    }
  }
}

// Using optional chaining with function calls
function doSomething(onContent, onError) {
  try {
    // ... do something with the data
  } catch (err) {
    // no exception if onError is undefined
    onError?.(err.message);
  }
}

Optional chaining with expressions

let nestedProp = obj?.['prop' + 'Name'];

Optional chaining with an array

let arrayItem = arr?.[42];

Optional chaining is forbidden in write contexts such as a?.b = c.
Optional deletion as in: delete a ?.b is supported.

Let's see what babel transpiler does with this Optional chaining syntax

const nameLength = db?.user;

It transpile into

var _db;

var nameLength = (_db = db) === null || _db === void 0 ? void 0 : _db.user;

If you don't know what void 0 does, it evaluates the given expression and then returns undefined.

Syntax

obj?.prop; // Object
obj?.[expr]; // Expressions
arr?.[index]; // Array
func?.(args); // Function calls

Resources

Thanks for reading!

Setting Up Your React Project

Vinoth Kumar — Sun, 19 Jan 2020 17:57:18 +0000

In the section, we are going to see the necessary things to make sure before you start a react project. We are not going to do any changes in react, instead, we will focus on stuff that needs to be done before that.

You can consider this section as a to-do list for setting up a react project.

We are going to use VS Code in our case

What is React?

React is an open-source JavaScript library for building user interfaces which were created by Jordan Walk and maintained by Facebook and a community of individual developers and companies.

Why Create React App?

Create React App (CRA) is an officially and easiest way to get started building React applications.

Quick Start

npx create-react-app demo
code demo

ESLint

ESLint is a static code analysis tool for identifying problematic patterns found in JavaScript code.

Install ESLint in your code editor.

Create a .eslintrc file in the root directory of the project.

{
  "extends": ["react-app", "plugin:jsx-a11y/strict"]
}

EditorConfig

Why EditorConfig?

EditorConfig helps maintain consistent coding styles for multiple developers working on the same project across various editors and IDEs.

Install EditorConfig in your code editor.

Create a .editorconfig file in the root directory of the project.

root = true

[*]
charset = utf-8
end_of_line = lf
indent_size = 2
indent_style = space
insert_final_newline = true
max_line_length = 80
trim_trailing_whitespace = true

[*.md]
max_line_length = 0
trim_trailing_whitespace = false

[COMMIT_EDITMSG]
max_line_length = 0

Prettier

Prettier is a code formatter.

Add Prettier to your editor.

Create a .prettierrc file in the root directory of the project.

{
  "tabWidth": 2,
  "semi": true,
  "singleQuote": true,
  "jsxSingleQuote": true
}

Add or remove rules according to your convenience

Go to VS Code Setting

Search for "Editor: Formate On Save" and make sure you check the box to formate the code when you save the file.

If you are in the middle of the project and the codes are not formatted well you can do then as well.

npx prettier --write "src/**/*.{js,jsx,json,css,scss,md}"

Checklist

ESLint
EditorConfig
Prettier

Resources

Thanks for reading!