ECS - Elastic Container Service

• ECS tasks can also be assigned with IAM ROLES just like IAM Role or EC2 instances

• Task definitions

  • Container information for your application

    • Docker image to use with each container , Docker networking mode

    • CPU and memory to use with each task

    • The IAM role that your tasks should use

    • The launch type to use (EC2 or Fargate)

    • The logging configuration,

    • what to do in case of failures

    • The command the container should run when it is started

    • Any data volumes that should be used with the containers in the task

• ECS Task placement

  • Task placement strategies

    • Algorithm for selecting instances for task placement or tasks for termination.

    • binpack

      • minimizes the number of instances in use

      • Place tasks based on the least available amount of CPU or memory

    • random

      • randomly place the tasks

      • requires the LEAST amount of configuration (EASIEST)

      • follow the constraints that you specified both implicitly or explicitly

      • it makes sure that tasks are scheduled on instances with enough resources to run them

    • spread

      • Place tasks evenly based on the specified value

        • Host (instanceId)

        • Availability Zone ( attributes:ecs.availabiltiy-zone)

  • Task placement constraints

    • Rule that is considered during task placement.

    • Ex: place tasks based on Availability Zone or instance type

    • distinctInstance

      • Place each task on a different container instance

    • memberOf

      • based on expression

    • Task groups: set of related tasks

  • Cluster query language

    • Expressions that enable you to group objects

    • you can group container instances by Availability Zone, Instance type, or custom metadata

  • Task placement constraints place the tasks, but Cluster query language is the one which provides you with expression to group the task

  • Task placement strategies and constraints are usually used together

  • Task placement strategies and constraints are NOT supported for tasks using the Fargate launch type.

  • Fargate tasks are spread across Availability Zones

  • https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-placement-strategies.html

• ECS Deployment types

  • Rolling update

    • Amazon ECS service scheduler replaces the currently running tasks with new tasks

  • Blue/Green deployment with CodeDeploy

    • Controlled by CodeDeploy

    • enables you to verify a new deployment of a service before sending production traffic to it

    • Canary: Traffic is shifted in two increments.

    • Linear: Traffic is shifted in equal increments with an equal number of minutes between each increment

    • All-at-once: All traffic is shifted from the original task set to the updated task set all at once.

  • External Deployment

    • third-party deployment

• ECR

  • Fully Managed Docker container registry provided by AWS

  • Alternative to Docker Hub