To run Docker containers with ECS, you first define an [ECS Task](http://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_defintions.html), which is a JSON file that describes what container(s) to run, the resources (memory, CPU) those containers need, the volumes to mount, the environment variables to set, and so on. To actually run an ECS Task, you define an ECS Service, which can: 1. Deploy the requested number of Tasks across an ECS cluster based on the `desired_number_of_tasks` input variable. 2. Restart tasks if they fail.