feat(sns): support cross-region subscription on imported topics (#4917)

Use the 'region' property on subscribing to imported SNS topics so that
the user can avail cross-region subscriptions.

fixes #3842

packages/@aws-cdk/aws-sns-subscriptions/lib/sqs.ts

@@ -1,7 +1,7 @@
 import iam = require('@aws-cdk/aws-iam');
 import sns = require('@aws-cdk/aws-sns');
 import sqs = require('@aws-cdk/aws-sqs');
-import { Construct } from '@aws-cdk/core';
+import { Construct, Stack } from '@aws-cdk/core';
 import { SubscriptionProps } from './subscription';
 
 /**
@@ -50,6 +50,15 @@ export class SqsSubscription implements sns.ITopicSubscription {
       protocol: sns.SubscriptionProtocol.SQS,
       rawMessageDelivery: this.props.rawMessageDelivery,
       filterPolicy: this.props.filterPolicy,
+      region: this.regionFromArn(topic),
     };
   }
+
+  private regionFromArn(topic: sns.ITopic): string | undefined {
+    // no need to specify `region` for topics defined within the same stack
+    if (topic instanceof sns.Topic) {
+      return undefined;
+    }
+    return Stack.of(topic).parseArn(topic.topicArn).region;
+  }
 }

packages/@aws-cdk/aws-sns-subscriptions/test/subs.test.ts

@@ -2,7 +2,7 @@ import '@aws-cdk/assert/jest';
 import lambda = require('@aws-cdk/aws-lambda');
 import sns = require('@aws-cdk/aws-sns');
 import sqs = require('@aws-cdk/aws-sqs');
-import { SecretValue, Stack } from '@aws-cdk/core';
+import { CfnParameter, SecretValue, Stack } from '@aws-cdk/core';
 import subs = require('../lib');
 
 // tslint:disable:object-literal-key-quotes
@@ -550,3 +550,26 @@ test('with filter policy', () => {
     }
   });
 });
+
+test('region property is present on an imported topic', () => {
+  const imported = sns.Topic.fromTopicArn(stack, 'mytopic', 'arn:aws:sns:us-east-1:1234567890:mytopic');
+  const queue = new sqs.Queue(stack, 'myqueue');
+  imported.addSubscription(new subs.SqsSubscription(queue));
+
+  expect(stack).toHaveResource('AWS::SNS::Subscription', {
+    Region: 'us-east-1'
+  });
+});
+
+test('region property on an imported topic as a parameter', () => {
+  const topicArn = new CfnParameter(stack, 'topicArn');
+  const imported = sns.Topic.fromTopicArn(stack, 'mytopic', topicArn.valueAsString);
+  const queue = new sqs.Queue(stack, 'myqueue');
+  imported.addSubscription(new subs.SqsSubscription(queue));
+
+  expect(stack).toHaveResource('AWS::SNS::Subscription', {
+    Region: {
+      "Fn::Select": [ 3, { "Fn::Split": [ ":", { "Ref": "topicArn" } ] } ]
+    }
+  });
+});

packages/@aws-cdk/aws-sns/lib/subscription.ts

@@ -34,6 +34,13 @@ export interface SubscriptionOptions {
    * @default - all messages are delivered
    */
   readonly filterPolicy?: { [attribute: string]: SubscriptionFilter };
+
+  /**
+   * The region where the topic resides, in the case of cross-region subscriptions
+   * @link https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-sns-subscription.html#cfn-sns-subscription-region
+   * @default - the region where the CloudFormation stack is being deployed.
+   */
+  readonly region?: string;
 }
 /**
  * Properties for creating a new subscription
@@ -85,6 +92,7 @@ export class Subscription extends Resource {
       topicArn: props.topic.topicArn,
       rawMessageDelivery: props.rawMessageDelivery,
       filterPolicy: this.filterPolicy,
+      region: props.region,
     });
 
   }