Amazon ECS task definitions - Amazon Elastic Container Service
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Amazon ECS task definitions

A task definition is a blueprint for your application. It is a text file in JSON format that describes the parameters and one or more containers that form your application.

The following are some of the parameters that you can specify in a task definition:

  • The launch type to use, which determines the infrastructure that your tasks are hosted on

  • The Docker image to use with each container in your task

  • How much CPU and memory to use with each task or each container within a task

  • The memory and CPU requirements

  • The operating system of the container that the task runs on

  • The Docker networking mode to use for the containers in your task

  • The logging configuration to use for your tasks

  • Whether the task continues to run if the container finishes or fails

  • The command that the container runs when it's started

  • Any data volumes that are used with the containers in the task

  • The IAM role that your tasks use

For a complete list of task definition parameters, see Amazon ECS task definition parameters for the Fargate launch type.

After you create a task definition, you can run the task definition as a task or a service.

  • A task is the instantiation of a task definition within a cluster. After you create a task definition for your application within Amazon ECS, you can specify the number of tasks to run on your cluster.

  • An Amazon ECS service runs and maintains your desired number of tasks simultaneously in an Amazon ECS cluster. How it works is that, if any of your tasks fail or stop for any reason, the Amazon ECS service scheduler launches another instance based on your task definition. It does this to replace it and thereby maintain your desired number of tasks in the service.

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