feat(sns-subscriptions): cross-region support for Lambda functions

packages/@aws-cdk/aws-sns-subscriptions/README.md

@@ -19,6 +19,8 @@ Subscriptions can be added to the following endpoints:
 * AWS Lambda
 * Email
 
+Subscriptions to Amazon SQS and AWS Lambda can be added on topics across regions.
+
 Create an Amazon SNS Topic to add subscriptions.
 
 ```ts

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

@@ -1,7 +1,7 @@
 import * as iam from '@aws-cdk/aws-iam';
 import * as lambda from '@aws-cdk/aws-lambda';
 import * as sns from '@aws-cdk/aws-sns';
-import { Construct } from '@aws-cdk/core';
+import { Construct, Stack } from '@aws-cdk/core';
 import { SubscriptionProps } from './subscription';
 
 /**
@@ -35,6 +35,15 @@ export class LambdaSubscription implements sns.ITopicSubscription {
       endpoint: this.fn.functionArn,
       protocol: sns.SubscriptionProtocol.LAMBDA,
       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

@@ -736,7 +736,7 @@ test('with filter policy', () => {
   });
 });
 
-test('region property is present on an imported topic', () => {
+test('region property is present on an imported topic - sqs', () => {
   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));
@@ -746,7 +746,7 @@ test('region property is present on an imported topic', () => {
   });
 });
 
-test('region property on an imported topic as a parameter', () => {
+test('region property on an imported topic as a parameter - sqs', () => {
   const topicArn = new CfnParameter(stack, 'topicArn');
   const imported = sns.Topic.fromTopicArn(stack, 'mytopic', topicArn.valueAsString);
   const queue = new sqs.Queue(stack, 'myqueue');
@@ -758,3 +758,34 @@ test('region property on an imported topic as a parameter', () => {
     },
   });
 });
+
+test('region property is present on an imported topic - lambda', () => {
+  const imported = sns.Topic.fromTopicArn(stack, 'mytopic', 'arn:aws:sns:us-east-1:1234567890:mytopic');
+  const func = new lambda.Function(stack, 'MyFunc', {
+    runtime: lambda.Runtime.NODEJS_10_X,
+    handler: 'index.handler',
+    code: lambda.Code.fromInline('exports.handler = function(e, c, cb) { return cb() }'),
+  });
+  imported.addSubscription(new subs.LambdaSubscription(func));
+
+  expect(stack).toHaveResource('AWS::SNS::Subscription', {
+    Region: 'us-east-1',
+  });
+});
+
+test('region property on an imported topic as a parameter - lambda', () => {
+  const topicArn = new CfnParameter(stack, 'topicArn');
+  const imported = sns.Topic.fromTopicArn(stack, 'mytopic', topicArn.valueAsString);
+  const func = new lambda.Function(stack, 'MyFunc', {
+    runtime: lambda.Runtime.NODEJS_10_X,
+    handler: 'index.handler',
+    code: lambda.Code.fromInline('exports.handler = function(e, c, cb) { return cb() }'),
+  });
+  imported.addSubscription(new subs.LambdaSubscription(func));
+
+  expect(stack).toHaveResource('AWS::SNS::Subscription', {
+    Region: {
+      'Fn::Select': [ 3, { 'Fn::Split': [ ':', { 'Ref': 'topicArn' } ] } ],
+    },
+  });
+});