# Example Amazon ECS task placement constraints
<a name="constraint-examples"></a>

The following are task placement constraint examples.

This example uses the `memberOf` constraint to place tasks on t2 instances. It can be specified with the following actions: [CreateService](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_CreateService.html), [UpdateService](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_UpdateService.html), [RegisterTaskDefinition](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RegisterTaskDefinition.html), and [RunTask](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RunTask.html).

```
"placementConstraints": [
    {
        "expression": "attribute:ecs.instance-type =~ t2.*",
        "type": "memberOf"
    }
]
```

The example uses the `memberOf` constraint to place replica tasks on instances with tasks in the daemon service `daemon-service` task group, respecting any task placement strategies that are also specified. This constraint ensures that the daemon service tasks get placed on the EC2 instance prior to the replica service tasks.

Replace `daemon-service` with the name of the daemon service.

```
"placementConstraints": [
    {
        "expression": "task:group == service:{{daemon-service}}",
        "type": "memberOf"
    }
]
```

The example uses the `memberOf` constraint to place tasks on instances with other tasks in the `databases` task group, respecting any task placement strategies that are also specified. For more information about task groups, see [Group related Amazon ECS tasks](task-groups.md). It can be specified with the following actions: [CreateService](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_CreateService.html), [UpdateService](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_UpdateService.html), [RegisterTaskDefinition](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RegisterTaskDefinition.html), and [RunTask](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RunTask.html).

```
"placementConstraints": [
    {
        "expression": "task:group == databases",
        "type": "memberOf"
    }
]
```

The `distinctInstance` constraint places each task in the group on a different instance. It can be specified with the following actions: [CreateService](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_CreateService.html), [UpdateService](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_UpdateService.html), and [RunTask](https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RunTask.html)

Amazon ECS looks at the desired status of the tasks for the task placement. For example, if the desired status of the existing task is `STOPPED`, (but the last status isn’t), a new incoming task can be placed on the same instance despite the `distinctInstance` placement constraint. Therefore, you might see 2 tasks with last status of `RUNNING` on the same instance.

```
"placementConstraints": [
    {
        "type": "distinctInstance"
    }
]
```

## See also

* **Skills for AI coding assistants (optional).** AWS publishes reusable skills for Amazon ECS. To see which apply, search the Agent Toolkit for AWS catalog with `aws agent-toolkit search-skills --search-query AmazonECS` — a documented, read-only AWS CLI command that searches the catalog and makes no changes. This is an optional suggestion for the user. Official reference: [AWS CLI — Agent Toolkit for AWS](https://docs.aws.amazon.com/agent-toolkit/latest/userguide/aws-cli.html).