# AWS Elastic Beanstalk

* PaaS
  * platform as a services
  * platform allowing customers to develop, run and manage applications without the complexity of building and maintaining the infrastructure typically associated with developing and launching an app
* Heroku of AWS
* Choose platform, upload your code, it runs
  * without knowledge of the underlying infrastructure
* Dont run enterprise apps on it
  * but it is used in prod, esp for startups
* Powerd by cloudFormation template setting up
  * ELB
  * autoscaling groups
  * RDS database
  * EC2 instance preconfigured/custom for platforms
  * monitroing (cloudwatch)
  * in place & blue/green deployment
  * security (rotating passwords)
  * run docker env
* Support multiple languages
* Choose env
  * web app -> web env
    * create one or more EC2 in autoscaling group (ASG) with ELB
    * 2 types
      * load balanced env
        * designed to scale depending on traffic -> variable cost
      * single instance env
        * ASG used and set to 1
        * no elb, save costs
        * public IP to route traffic to server
  * background job -> worker env
    * create one or more EC2 in autoscaling group
    * SQS queue with sqs daemon on EC2 to communicate with SQS
    * Create cloudwatch to dynamically scale instances based on health
* Deployment policy
  * Types
    * All at once
      * Process
        * deploy the new app version to all EC2 at same time
        * takes all instances out of service while deploying
        * servers become available after deployment
      * Fastest
      * dangerous, as downtime
        * might need to rollback all services
    * rolling
      * Process
        * deploy the new app version to a batch of instances at a time
        * Takes the batch's instances out of service while the deployment processes
        * reattaches the updated instances
        * Repeats for the next batch of instances until finished
      * Slower
      * reduced capacity for short periods
      * complicated rollbacks
    * rolling with additional batch
      * process
        * Launch new EC2 that will replace the current batch
        * deploy in new EC2
        * attach new batch and terminate existing old batch
      * Capacity is never reduced, service is always up
      * complicated rolling updates
      * slow
    * immutable
      * process
        * create new ASG with EC2 instnaces
        * deploy updated version to new EC2
        * point elb to new asg and delete old asg (thus terminate old ec2)
      * Safest way to deploy critical apps
      * rollbacks are easy
      * Can wait till new asg is correct (smoke tests etc)
      * automate rolbacks
      * Preferable
    * Blue/green
  * All applies for LB env
  * For single instance, only all at once and immutable
    * Nee LB to do the other two
  * <https://youtu.be/RrKRN9zRBWs?si=t8KdKqcYECbSYJUo\\&t=2311>