# PlacementConstraint

The placement constraints to use for tasks in the service. For more information, see [Amazon ECS Task Placement Constraints](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-placement-constraints.html).

Tasks will only be placed on instances that match these rules.

- Source: [`aws-ecs/lib/placement.ts`](https://github.com/aws/aws-cdk/blob/v2.275.0/packages/aws-cdk-lib/aws-ecs/lib/placement.ts#L103)

## Example

```ts
const vpc = ec2.Vpc.fromLookup(this, 'Vpc', {
  isDefault: true,
});

const cluster = new ecs.Cluster(this, 'Ec2Cluster', { vpc });
cluster.addCapacity('DefaultAutoScalingGroup', {
  instanceType: new ec2.InstanceType('t2.micro'),
  vpcSubnets: { subnetType: ec2.SubnetType.PUBLIC },
});

const taskDefinition = new ecs.TaskDefinition(this, 'TD', {
  compatibility: ecs.Compatibility.EC2,
});

taskDefinition.addContainer('TheContainer', {
  image: ecs.ContainerImage.fromRegistry('foo/bar'),
  memoryLimitMiB: 256,
});

const runTask = new tasks.EcsRunTask(this, 'Run', {
  integrationPattern: sfn.IntegrationPattern.RUN_JOB,
  cluster,
  taskDefinition,
  launchTarget: new tasks.EcsEc2LaunchTarget({
    placementStrategies: [
      ecs.PlacementStrategy.spreadAcrossInstances(),
      ecs.PlacementStrategy.packedByCpu(),
      ecs.PlacementStrategy.randomly(),
    ],
    placementConstraints: [
      ecs.PlacementConstraint.memberOf('blieptuut'),
    ],
  }),
  propagatedTagSource: ecs.PropagatedTagSource.TASK_DEFINITION,
});
```

## Methods

- `distinctInstances(): PlacementConstraint // chainable` (static) — Use distinctInstance to ensure that each task in a particular group is running on a different container instance.

- `memberOf(...expressions: string[]): PlacementConstraint // chainable` (static) — Use memberOf to restrict the selection to a group of valid candidates specified by a query expression.

  Multiple expressions can be specified. For more information, see
  [Cluster Query Language](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/cluster-query-language.html).

  You can specify multiple expressions in one call. The tasks will only be placed on instances matching all expressions.

- `toJson(): CfnService.PlacementConstraintProperty[]` — Return the placement JSON.