Amazon ECS Task Definitions
A task definition is required to run Docker containers in Amazon ECS. Some of the parameters you can specify in a task definition include:
Which Docker images to use with the containers in your task
How much CPU and memory to use with each container
Whether containers are linked together in a task
What (if any) ports from the container are mapped to the host container instance
Whether the task should continue to run if the container finishes or fails
The command the container should run when it is started
What (if any) environment variables should be passed to the container when it starts
Any data volumes that should be used with the containers in the task
What (if any) IAM role your tasks should use for permissions
You can define multiple containers and data volumes in a task definition. For a complete description of the parameters available in a task definition, see Task Definition Parameters.
Your entire application stack does not need to exist on a single task definition, and in most cases it should not. Your application can span multiple task definitions by combining related containers into their own task definitions, each representing a single component. For more information, see Application Architecture.