> For the complete documentation index, see [llms.txt](https://ysfang82.gitbook.io/development-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ysfang82.gitbook.io/development-notes/aws-notes/service/compute-and-load-balancing/ecs.md).

# ECS

**Introduction**

* Elastic Container Service (ECS) manages Docker applications across a cluster. It's regional.

**Feature**

* Task Definition
  * Specify one or more containers, including:
    * Docker repository and image
    * memory and CPU
    * shared data volumes
    * Network mode:
      * `none`
      * `bridge` (default): utilizes Docker's built-in virtual network which runs inside the instance.
      * `awsvpc`: each task is allocated an ENI, and must have a NetworkConfiguration for the ECS service. (provides more control over bridge mode)
      * `host`: bypasses virtual network to the instance's network directly. Can't run multiple instantiations of the same task on a single container instance when port mappings are used.
* ECS Cluster can contain multiple different container instance types.
* Can create IAM policies for Clusters, Task Execution roles.
* Schedule ECS in 2 ways:
  * Service Scheduler
  * Custom Scheduler
* Can use ECS agent (Linux only) to connect to EC2 instances of the Cluster.
* Security Groups operate at instance level, not at the task or container level.
* ECS can't be the origin of CloudFront.

**Reference**

* Docker
  * Packages code, configurations, dependencies into containers (standard units).
  * Docker is infinitely scalable so running docker on AWS is a great way to run distributed applications at any scale.
  * Strength:
    * No more dependency hell
    * Consistent progression from DEV -> TEST -> QA -> UAT -> PROD
    * Isolation (applications are devided into different containers)
    * Extreme code portability
    * Microservices
* Virtualization vs Contrainerization:\
  ![](https://3303577320-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4cDbT2F2VmcAohuhSN%2F-M4cDbsP_Q866yrLCgLp%2F-M4cDmT0-vlBhXBCPiQj%2FVirtualisation%20vs%20Containerisation.png?generation=1586591644516359\&alt=media)