EC2 Container Service (ECS) Essentials:

• ECS is a container management service that supports Docker.
• It allows you to easily create and mange a fleet of Docker containers on a cluster of EC2 instances.

Why use ECS/Containers?

• Create distributed application and Microservices:
  • Create application architecture comprised of independent tasks or processes (micro services).
  • For example, you can have separate containers for various components of your application:
    • Webserver
    • Application server
    • Message queue
    • Backend servers
  • This allows you to start, stop, manage, monitor and scale each container independently.
• Batch and ETL Jobs:
  • Package batch and ETL jobs into containers and deploy them into an shared EC2 cluster(s).
  • Run different versions of the same job or multiple jobs on the same cluster.
  • Share cluster capacity with other processes and or grow job dynamically on-demand to improve resource utilization.
• Continuous Integration and Deployment
  • By using Dockers Image versioning, and create a Docker Image that can be deployed into your containers.
  • This allows you to avoid an application from working in a developer environment and not working in a production environment because the Docker daemon is the same across all environment.

Dockerfile:

• A plain text file (script) that specifies all of the components that are included in the container.
• Basically, it's the instructions for what will be placed inside a given container.

Container/Docker Image:

• A container/docker image is built from a Dockerfile.
• The container/docker image contains all the downloaded software, code, runtime, system tools, and libraries (as outlined in the Dockfile).
  • i.e. if the Dockerfile specifies PHP to be downloaded and installed, then the container/docker image will have PHP downloaded an installed.

Container Registry:

• A container registry is a repository where container/docker images are stored and accessed from when needed.

• A container registry can be:

  • Located on AWS via the ECR service (EC2 Container Registry).

  A 3rd party repository like Docker Hub.

  • Self-hosted registry.

ECS Task Definition:

• A JSON formatted text file that contains the "blueprint" for your application, including:
  • Which container/docker image to use.
  • The repository (container registry) the image is located in.
  • Which ports should be open on the container instance.
  • What data volumes should be used with the containers.

ECS Agent:

• The ECS Agent runs on each EC2 instance in the ECS cluster.
• It communicates information about the instances to ECS, including:
  • Running tasks.
  • Resource utilization.
• The ECS Agent is also responsible for starting/stopping tasks (when told to by ECS).

ECS Task:

• An ECS Task is the actual representation of the Task Definition on an EC2 instance inside of your container cluster.
• The ECS Agent will start/stop these tasks based on instruction/schedule.