feat(ecs): give cluster a method that provides task arn

packages/aws-cdk-lib/aws-ecs/README.md

@@ -186,6 +186,15 @@ const capacityProvider = new ecs.AsgCapacityProvider(this, 'AsgCapacityProvider'
 cluster.addAsgCapacityProvider(capacityProvider);
 ```
 
+It is also possible to obtain the ARN of a task based on the key pattern from Cluster.
+
+```ts
+const cluster = new ecs.Cluster(this, 'Cluster', {
+  vpc,
+});
+const taskArn = cluster.arnForTasks('*') // arn:aws:ecs:<region>:<account>:task/<clusterName>/*
+```
+
 
 ### Bottlerocket
 

packages/aws-cdk-lib/aws-ecs/lib/cluster.ts

@@ -583,6 +583,16 @@ export class Cluster extends Resource implements ICluster {
     }
   }
 
+  /**
+   * Returns an ARN that represents all tasks within the cluster that match
+   * the task pattern specified. To represent all tasks, specify ``"*"``.
+   *
+   * @param keyPattern Task id pattern
+   */
+  public arnForTasks(keyPattern: string): string {
+    return this.clusterArn.replace(/cluster\/(.*)$/, `task/$1/${keyPattern}`);
+  }
+
   private configureWindowsAutoScalingGroup(autoScalingGroup: autoscaling.AutoScalingGroup, options: AddAutoScalingGroupCapacityOptions = {}) {
     // clear the cache of the agent
     autoScalingGroup.addUserData('Remove-Item -Recurse C:\\ProgramData\\Amazon\\ECS\\Cache');

packages/aws-cdk-lib/aws-ecs/test/cluster.test.ts

@@ -1055,6 +1055,20 @@ describe('cluster', () => {
     expect(cluster.defaultCloudMapNamespace!.namespaceName).toBe('foo');
   });
 
+  test('arnForTasks returns a task arn from key pattern', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'MyVpc', {});
+    const cluster = new ecs.Cluster(stack, 'EcsCluster', { vpc });
+    const taskIdPattern = 'taskIdPattern';
+
+    // THEN
+    const taskArn = cluster.arnForTasks(taskIdPattern);
+    expect(taskArn).toEqual(
+      `arn:aws:ecs:${cluster.env.region}:${cluster.env.account}:task/${cluster.clusterName}/${taskIdPattern}`,
+    );
+  });
+
   /*
    * TODO:v2.0.0 END OF OBSOLETE BLOCK
    */