chore(codepipeline): add example of an ECS Deploy Action

packages/@aws-cdk/aws-codepipeline-actions/README.md

@@ -809,6 +809,25 @@ Here's an example:
 
 [example ECS pipeline for an application in a separate source code repository](test/integ.pipeline-ecs-separate-source.lit.ts)
 
+#### Deploying to an existing ECS service across account and/or regions
+
+CodePipeline can deploy to an existing ECS service, even across accounts and/or regions.
+This requires importing the ECS service in the pipeline stack using the service's full ARN,
+which is then used to determine the correct account and region for the ECS Action.
+Here's an example:
+
+[example pipeline deploying to an existing ECS service cross account and region](test/integ.ecs-pipeline-cross-region-account-existing.lit.ts)
+
+#### Deploying to a new ECS service across account and/or regions
+
+CodePipeline can also deploy to a new ECS service across accounts and/or regions.
+This can be accomplished by using the `Stack.formatArn` method to save the full ARN of the service,
+which can then be used to import the ECS service in the pipeline stack,
+and the region and account of the ECS Action will be determined from that ARN.
+Here's an example:
+
+[example pipeline deploying to a new ECS service cross account and region](test/integ.ecs-pipeline-cross-region-account-new.lit.ts)
+
 ### AWS S3 Deployment
 
 To use an S3 Bucket as a deployment target in CodePipeline:

packages/@aws-cdk/aws-codepipeline-actions/test/ecs-pipeline-cross-region-account-helpers.ts

@@ -0,0 +1,39 @@
+import * as codepipeline from '@aws-cdk/aws-codepipeline';
+import * as s3 from '@aws-cdk/aws-s3';
+import * as cdk from '@aws-cdk/core';
+import { Construct } from 'constructs';
+import * as cpactions from '../lib';
+
+/**
+ * This is our pipeline which has initial actions.
+ */
+export class EcsServiceCrossRegionAccountPipelineStack extends cdk.Stack {
+  public artifact: codepipeline.Artifact;
+  public pipeline: codepipeline.Pipeline;
+
+  constructor(scope: Construct, id: string, props: cdk.StackProps) {
+    super(scope, id, props);
+
+    const artifact = new codepipeline.Artifact('Artifact');
+    this.artifact = artifact;
+    const bucket = new s3.Bucket(this, 'PipelineBucket', {
+      versioned: true,
+      removalPolicy: cdk.RemovalPolicy.DESTROY,
+    });
+    const source = new cpactions.S3SourceAction({
+      actionName: 'Source',
+      output: artifact,
+      bucket,
+      bucketKey: 'key',
+    });
+    this.pipeline = new codepipeline.Pipeline(this, 'Pipeline', {
+      stages: [
+        {
+          stageName: 'Source',
+          actions: [source],
+        },
+      ],
+    });
+
+  }
+}