"EC2 Container Service"

Posted on Mon 01 December 2014 in cloud

At AWS re:Invent (November 2014) a new technology was introduced. This was the AWS EC2 Container Service. A service provided by AWS to run docker containers on top of EC2 instances.

We have been using docker for a while now within our organization, and I have to say that I am a huge fan of Docker. This is a great step in the right direction and I believe can help to decrease deploys to AWS while increasing stability and extensibility of a given architecture.

EC2 Container Service

At this point in time EC2 Container Service is still in preview, which means that you will need to request access to this preview in your own AWS account to follow this pattern. However AWS does have some great material that will allow you to see the benefits of this new service without requiring you to have preview access. This material can be found here.

Service Breakdown

The main idea of this service is to give you the ability to create complese architectures that can be broken down into smaller docker containers, which in turn can be deployed to a cluster of actual ec2 instances. This meanst hat you could have a single m3.xlarge instance for your application while keeping the database and application code seperate, but without requiring you to have more instances than absolutely necessary.

The service pieces are broken down into the following.

  1. Tasks
  2. Containers
  3. Clusters
  4. Container Instances

Tasks

Tasks are basically the starting point of your cluster deploy. Anytime you want to deploy your application you will start by defining the task. Tasks themselves are defined as json objects.

{
  "family": "application-name",
  "version": "9a56714245e7e603127",    -- This can be a simple version or git SHA1
  "containers": [
    << CONTAINER DEFINITIONS >>
  ]
}

So with this json definition we are defining the entire application that we are providing, so if I had an application that acted as an API endpoint I would provide the load balancing server as a container, the actual web server as a container and then a container for the database (if one exists).

When you have your task defined, you can register that task with EC2 Container Service to specify that you have the new task.

aws ecs register-task-definition --family "custom-name" --version "custom-version" definition.json

After you have registered the task and you have the cluster created you can run the task using the following command.

aws ecs run-task custom-name:custom-version

Containers

Container definitions are very simple and can follow a lot of the docker idioms in creation.

{
  "name": "container-name", 
  "image": "app-container:latest", 
  "cpu": 128,                        -- Note CPU is in units, defines the instances that can fit a given instance
  "memory": 512,
  "portMappings": [
    {
      "containerPort": 9443, 
      "hostPort": 443 
    }
  ], 
  "links": ["frontend"], 
  "essential": true
}

So the main things to understand on this definition is the cpu field. This represents the unit of measurement for a cpu that should be used. You can think of this as almost a percentage of the total CPU to use (which I believe 100% would be 1024). So if I wanted to use 50% of the cpu for a given instance I would have "cpu": 512.

The links is the list of containers that this container should reference, you can find information about linking containers on the docker documentation site.

Finally the essential flag is set to let the cluster know if the task is basically good or not. If a single container is essential, but cannot be created or fails to run, this would mean the task is not valid anymore.

Clusters

Clusters are basically grouping of container instances that are releated for a given task. When the cluster is first created it is empty and it then populates with container as requirements come into play.

AWS does have a command line tool that you can use to create a cluster.

aws ec2 create-cluster cluster-name

This will create a cluster an give you the ability to start creating container instances that can be part of this cluster. When this cluster is created you will be given an arn to reference this cluster. This is a very similar process to SQS, SNS, etc.

Container Instances

These are instances that AWS have setup with a go application (container agent) that will tie into the cluster mechanism.

Conclusion

While I have not yet been able to test out ECS I am very excited about this service and very excited about the flow they have created as I feel that it allows us to create much more stable and scalable systems.

Once I have access to the preview I will add my experiences in a follow-up post.