Amazon EC2 Container Service
Developer Guide (API Version 2014-11-13)

Application Architecture

When you’re considering how to model task definitions and services, it helps to think about what processes need to run together on the same instance and how you will scale each component. As an example, imagine an application that consists of the following components:

  • A front-end service that displays information on a web page

  • A back-end service that provides APIs for the front-end service

  • A data store

In your development environment, you probably run all three containers together on your Docker host. You might be tempted to use the same approach for your production environment, but this approach has several drawbacks:
  • Changes to one component can impact all three components, which may be a larger scope for the change than you want

  • Each component is more difficult to scale because you have to scale every container proportionally

  • Task definitions can only have 10 container definitions and your application stack might require more, either now or in the future

  • Every container in a task definition must land on the same container instance, which may limit your instance choices to the largest sizes

Instead, you should create task definitions that group the containers that are used for a common purpose, and separate the different components into multiple task definitions. In this example, three task definitions each specify one container. The example cluster below has three container instances registered with three front-end service containers, two back-end service containers, and one data store service container.

                Application architecture example

You can group related containers in a task definition, such as linked containers that must be run together. For example, you could add a log streaming container to your front-end service and include that in the same task definition.

After you have your task definitions, you can create services from them to maintain the availability of your desired tasks. For more information, see Creating a Service. In your services, you can associate containers with Elastic Load Balancing load balancers. For more information, see Service Load Balancing. When your application requirements change, you can update your services to scale the number of desired tasks up or down, or to deploy newer versions of the containers in your tasks. For more information, see Updating a Service.