Amazon S3

Simple Storage Service

• Files can be stored and retrieved from  anywhere on the web .

• Used for live streaming . Netflix, Hotstar use it for hosting.

• Used for content distribution , big data analytics , backup etc .

• Files are stored in buckets , a max of 100 buckets can be created by a developer .
  
• Replica of the file is available in 3 different Availability Zones , all in the same region . AWS also supports cross region replication which can be configured manually .
  
• Supports periodic automatic archival/deletion , using lifecycle rules.
  

Storage class
Standard available in 3 availability zone
Glacier : cold data.
Archival data ..
Glacier deep
Long data retention

Requester pays
The one who download pays

Object lifecycle management
Move file automatically to glacier after 50 days
Cannot move back from glacier to S3 via lifecycle

Retreival options

EFS : multiple EC2 share same storage .
Nfs : network file system.

Snowball.
Hardware device to migrate a data .
Like a briefcase .
Device will be shipped.

Aws elastic block storage

IaaS

Infrastructure as a Service  :

 provides access to virtual or physical hardware .

EBS

     Elastic Block Storage

• Similar to a hard drive
• Block storage for EC2 and other services
• Automatic replication within its AZ
• Snapshot backup to Amazon S3
• Restore a snapshot to a new EBS volume
• Multiple volumes can be attached a single EC2
  
• Volumes can be shared between multiple EC2
  

SSD
HDD

Amazon ECS

ECS supports docker

Eliminate need to install operate your cluster.

Fleet of docker container

Fargate : managed ECS .
Next step to ECS.

Container as a Service

AWS Auto Scaling

• AWS Auto Scaling

  Before getting start , lets revisit the following topics .

s

EC2

  Create an Elastic Cloud Compute instance . This is like linux server where you are going to deploy your application code . For Example , if you want to host a Web Application which runs on Node.js , you need to install Node.js and run you Web Application .

 a

VPC

Create an Amazon Machine Image of an EC2 instance .

a

AMI 

Create an Amazon Machine Image of an EC2 instance .

a

s

Load Balancer

Application Load Balancer : used for Http and Https

Network Load Balancer : used for TCP,UDP and TLS .

a

s

Auto Scaling Group

 a

a

s

Scaling Policy

 a

a

s

CloudWatch

 a

s

CloudWatch Alarms

 a

 a

S3

Simple storage service . Static files of the application can be placed in S3 to reduce the load on the application .

 a

CloudFront

Simple storage service . Static files of the application can be placed in S3 to reduce the load on the application .

a

Error: Objects are not valid as a React child

Error Blog 

This blog is about the error Error: Objects are not valid as a React child 

Problem Statement

error on start of reactjs application

Error Details 

error Log

ERROR DETAILS 

Error: Objects are not valid as a React child (found: object with keys {TASK_ID, TASK_DESC, TASK_REF, TASK_STATUS, UPDATED_ON}). If you meant to render a collection of children, use an array instead. in div (at task-list.js:22) in TaskList (at App.js:10) in div (at App.js:9) in App (at src/index.js:9) in StrictMode (at src/index.js:8)

Error Code 

You will face this error if you try to convert an array response to json .

router.get('/', function (req, res) { Task.getAllTask(function (err, task) { console.log('controller') if (err) res.send(err); console.log('res', task); res.send( task); }); });

Solution

change the code so that the array is handled .

Code Changes 

wrap the array inside a json .

  

        

    

router.get('/', function (req, res) { Task.getAllTask(function (err, task) { console.log('controller') if (err) res.send(err); console.log('res', task); res.send({'resp':task}); }); });

         

OUTPUT

works 

Thanks for reading . Let me know your thoughts in the comments below    .

TypeError: Class extends value undefined is not a constructor or null

Error Blog 

This blog is about the error TypeError: Class extends value undefined is not a constructor or null

Problem Statement

unable to start reactjs application

Error Details 

error Log

ERROR DETAILS 

Uncaught TypeError: Class extends value undefined is not a constructor or null
    at Module../src/task/task-list.js (task-list.js:5)
    at __webpack_require__ (bootstrap:784)
    at fn (bootstrap:150)
    at Module../src/App.js (App.css?4433:45)
    at __webpack_require__ (bootstrap:784)
    at fn (bootstrap:150)
    at Module../src/index.js (index.css?f3f6:45)
    at __webpack_require__ (bootstrap:784)
    at fn (bootstrap:150)
    at Object.1 (task.js:11)
    at __webpack_require__ (bootstrap:784)
    at checkDeferredModules (bootstrap:45)
    at Array.webpackJsonpCallback [as push] (bootstrap:32)
    at main.chunk.js:1

Error Code 

You will face this error if you have improper syntax in extends React.Component.

import React from 'react';

class TaskList extends React.Component() {

  constructor() {

    super();

    this.state = {

      name: 'React',assetName:"asset name"

    };

  }

 

  render() {

     return (

    <div  >

       Task List

    </div>

  );

  }

}

export default TaskList;

Solution

change the code so that the syntax is proper for extends  . .

Code Changes 

add the following import in your component.ts file .

  

        

     class TaskList extends React.Component  {

         

OUTPUT

works 

Thanks for reading . Let me know your thoughts in the comments below    .

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

Error Blog 

This blog is about the error Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

Problem Statement

unable to start node js express application

Error Details 

error Log

ERROR DETAILS 

\node_modules\mysql\lib\protocol\Parser.js:437
      throw err; // Rethrow non-MySQL errors
      ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:470:11)
    at ServerResponse.header (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\express\lib\response.js:771:10)
    at ServerResponse.send (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\express\lib\response.js:267:15)
    at F:\ \study\gitRepo\new\learn\nodejs\expressjs\service\users.js:24:11
    at Query.<anonymous> (F:\ \study\gitRepo\new\learn\nodejs\expressjs\service\task.service.js:20:21)
    at Query.<anonymous> (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\Connection.js:526:10)
    at Query._callback (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\Connection.js:488:16)
    at Query.Sequence.end (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\protocol\sequences\Sequence.js:83:24)
    at Query._handleFinalResultPacket (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\protocol\sequences\Query.js:149:8)

Error Code 

You will face this error if you res.send twice in an express js application.

var express = require('express');

var router = express.Router();

var Task = require('./task.service.js');

router.get('/', function(req, res){

   Task.getAllTask(function(err, task) {

      console.log('controller')

      if (err)

        res.send(err);

        console.log('res', task);

      res.send(task);

    });

});

router.post('/create', function(req, res){

   console.log(req.body);

   var new_task = new Task(req.body);

   console.log(new_task);

   Task.createTask(new_task, function(err, task) {

    

      if (err)

        res.send(err);

      res.json(task);

    });

   res.send('success.');

});

//export this router to use in our index.js

module.exports = router;

Solution

change the code so that res.send is not called twice . .

Code Changes 

add the following import in your component.ts file .

  

        

      if (err)

        res.send(err);

      res.json(task);

    });

  // res.send('success.');

         

OUTPUT

works 

Thanks for reading . Let me know your thoughts in the comments below    .