feat(lambda): expose function.deadLetterQueue

Expose DLQ as a readonly attribute of the Function construct.

Fixes aws#6170

packages/@aws-cdk/aws-lambda/lib/function.ts

@@ -407,6 +407,11 @@ export class Function extends FunctionBase {
    */
   public readonly grantPrincipal: iam.IPrincipal;
 
+  /**
+   * The DLQ associated with this Lambda Function (this is an optional attribute).
+   */
+  public readonly deadLetterQueue?: sqs.IQueue;
+
   public readonly permissionsNode = this.node;
 
   protected readonly canCreatePermissions = true;
@@ -450,6 +455,8 @@ export class Function extends FunctionBase {
     const code = props.code.bind(this);
     verifyCodeConfig(code, props.runtime);
 
+    this.deadLetterQueue = this.buildDeadLetterQueue(props);
+
     const resource: CfnFunction = new CfnFunction(this, 'Resource', {
       functionName: this.physicalName,
       description: props.description,
@@ -467,7 +474,7 @@ export class Function extends FunctionBase {
       environment: Lazy.anyValue({ produce: () => this.renderEnvironment() }),
       memorySize: props.memorySize,
       vpcConfig: this.configureVpc(props),
-      deadLetterConfig: this.buildDeadLetterConfig(props),
+      deadLetterConfig: this.buildDeadLetterConfig(this.deadLetterQueue),
       tracingConfig: this.buildTracingConfig(props),
       reservedConcurrentExecutions: props.reservedConcurrentExecutions
     });
@@ -668,7 +675,7 @@ export class Function extends FunctionBase {
     };
   }
 
-  private buildDeadLetterConfig(props: FunctionProps) {
+  private buildDeadLetterQueue(props: FunctionProps) {
     if (props.deadLetterQueue && props.deadLetterQueueEnabled === false) {
       throw Error('deadLetterQueue defined but deadLetterQueueEnabled explicitly set to false');
     }
@@ -686,9 +693,17 @@ export class Function extends FunctionBase {
       resources: [deadLetterQueue.queueArn]
     }));
 
-    return {
-      targetArn: deadLetterQueue.queueArn
-    };
+    return deadLetterQueue;
+  }
+
+  private buildDeadLetterConfig(deadLetterQueue?: sqs.IQueue) {
+    if (deadLetterQueue) {
+      return {
+        targetArn: deadLetterQueue.queueArn
+      };
+    } else {
+      return undefined;
+    }
   }
 
   private buildTracingConfig(props: FunctionProps) {

packages/@aws-cdk/aws-lambda/test/test.function.ts

@@ -1,5 +1,6 @@
 import * as logs from '@aws-cdk/aws-logs';
 import * as s3 from '@aws-cdk/aws-s3';
+import * as sqs from '@aws-cdk/aws-sqs';
 import * as cdk from '@aws-cdk/core';
 import * as _ from 'lodash';
 import {Test, testCase} from 'nodeunit';
@@ -101,6 +102,54 @@ export = testCase({
     test.done();
   },
 
+  'dlq is returned when provided by user'(test: Test) {
+    const stack = new cdk.Stack();
+
+    const dlQueue = new sqs.Queue(stack, 'DeadLetterQueue', {
+      queueName: 'MyLambda_DLQ',
+      retentionPeriod: cdk.Duration.days(14)
+    });
+
+    const fn = new lambda.Function(stack, 'fn', {
+      handler: 'foo',
+      runtime: lambda.Runtime.NODEJS_10_X,
+      code: lambda.Code.fromInline('foo'),
+      deadLetterQueue: dlQueue,
+    });
+    const deadLetterQueue = fn.deadLetterQueue;
+    test.ok(deadLetterQueue?.queueArn);
+    test.ok(deadLetterQueue?.queueName);
+    test.ok(deadLetterQueue?.queueUrl);
+    test.done();
+  },
+
+  'dlq is returned when setup by cdk'(test: Test) {
+    const stack = new cdk.Stack();
+    const fn = new lambda.Function(stack, 'fn', {
+      handler: 'foo',
+      runtime: lambda.Runtime.NODEJS_10_X,
+      code: lambda.Code.fromInline('foo'),
+      deadLetterQueueEnabled: true,
+    });
+    const deadLetterQueue = fn.deadLetterQueue;
+    test.ok(deadLetterQueue?.queueArn);
+    test.ok(deadLetterQueue?.queueName);
+    test.ok(deadLetterQueue?.queueUrl);
+    test.done();
+  },
+
+  'dlq is undefined when not setup'(test: Test) {
+    const stack = new cdk.Stack();
+    const fn = new lambda.Function(stack, 'fn', {
+      handler: 'foo',
+      runtime: lambda.Runtime.NODEJS_10_X,
+      code: lambda.Code.fromInline('foo'),
+    });
+    const deadLetterQueue = fn.deadLetterQueue;
+    test.ok(deadLetterQueue === undefined);
+    test.done();
+  },
+
   'one and only one child LogRetention construct will be created'(test: Test) {
     const stack = new cdk.Stack();
     const fn = new lambda.Function(stack, 'fn', {