feat(elbv2): use addAction() on an imported application listener

packages/@aws-cdk/aws-elasticloadbalancingv2/lib/alb/application-listener.ts

@@ -508,6 +508,21 @@ export interface IApplicationListener extends IResource, ec2.IConnectable {
    * Don't call this directly. It is called by ApplicationTargetGroup.
    */
   registerConnectable(connectable: ec2.IConnectable, portRange: ec2.Port): void;
+
+  /**
+   * Perform the given action on incoming requests
+   *
+   * This allows full control of the default action of the load balancer,
+   * including Action chaining, fixed responses and redirect responses. See
+   * the `ListenerAction` class for all options.
+   *
+   * It's possible to add routing conditions to the Action added in this way.
+   *
+   * It is not possible to add a default action to an imported IApplicationListener.
+   * In order to add actions to an imported IApplicationListener a `priority`
+   * must be provided.
+   */
+  addAction(id: string, props: AddApplicationActionProps): void;
 }
 
 /**
@@ -627,6 +642,36 @@ abstract class ExternalApplicationListener extends Resource implements IApplicat
     // eslint-disable-next-line max-len
     throw new Error('Can only call addTargets() when using a constructed ApplicationListener; construct a new TargetGroup and use addTargetGroup.');
   }
+
+  /**
+   * Perform the given action on incoming requests
+   *
+   * This allows full control of the default action of the load balancer,
+   * including Action chaining, fixed responses and redirect responses. See
+   * the `ListenerAction` class for all options.
+   *
+   * It's possible to add routing conditions to the Action added in this way.
+   *
+   * It is not possible to add a default action to an imported IApplicationListener.
+   * In order to add actions to an imported IApplicationListener a `priority`
+   * must be provided.
+   */
+  public addAction(id: string, props: AddApplicationActionProps): void {
+    checkAddRuleProps(props);
+
+    if (props.priority !== undefined) {
+      // New rule
+      //
+      // TargetGroup.registerListener is called inside ApplicationListenerRule.
+      new ApplicationListenerRule(this, id + 'Rule', {
+        listener: this,
+        priority: props.priority,
+        ...props,
+      });
+    } else {
+      throw new Error('priority must be set for actions added to an imported listener');
+    }
+  }
 }
 
 /**

packages/@aws-cdk/aws-elasticloadbalancingv2/test/alb/listener.test.ts

@@ -707,6 +707,85 @@ describe('tests', () => {
     });
   });
 
+  test('Can add actions to an imported listener', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const stack2 = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'VPC');
+    const lb = new elbv2.ApplicationLoadBalancer(stack, 'LoadBalancer', {
+      vpc,
+    });
+    const listener = lb.addListener('Listener', {
+      port: 80,
+    });
+
+    // WHEN
+    listener.addAction('Default', {
+      action: elbv2.ListenerAction.fixedResponse(404, {
+        contentType: 'text/plain',
+        messageBody: 'Not Found',
+      }),
+    });
+
+    const importedListener = elbv2.ApplicationListener.fromApplicationListenerAttributes(stack2, 'listener', {
+      listenerArn: 'listener-arn',
+      defaultPort: 443,
+      securityGroup: ec2.SecurityGroup.fromSecurityGroupId(stack2, 'SG', 'security-group-id', {
+        allowAllOutbound: false,
+      }),
+    });
+    importedListener.addAction('Hello', {
+      action: elbv2.ListenerAction.fixedResponse(503),
+      conditions: [elbv2.ListenerCondition.pathPatterns(['/hello'])],
+      priority: 10,
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::ElasticLoadBalancingV2::Listener', {
+      DefaultActions: [
+        {
+          FixedResponseConfig: {
+            ContentType: 'text/plain',
+            MessageBody: 'Not Found',
+            StatusCode: '404',
+          },
+          Type: 'fixed-response',
+        },
+      ],
+    });
+
+    Template.fromStack(stack2).hasResourceProperties('AWS::ElasticLoadBalancingV2::ListenerRule', {
+      ListenerArn: 'listener-arn',
+      Priority: 10,
+      Actions: [
+        {
+          FixedResponseConfig: {
+            StatusCode: '503',
+          },
+          Type: 'fixed-response',
+        },
+      ],
+    });
+  });
+
+  test('actions added to an imported listener must have a priority', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+
+    const importedListener = elbv2.ApplicationListener.fromApplicationListenerAttributes(stack, 'listener', {
+      listenerArn: 'listener-arn',
+      defaultPort: 443,
+      securityGroup: ec2.SecurityGroup.fromSecurityGroupId(stack, 'SG', 'security-group-id', {
+        allowAllOutbound: false,
+      }),
+    });
+    expect(() => {
+      importedListener.addAction('Hello', {
+        action: elbv2.ListenerAction.fixedResponse(503),
+      });
+    }).toThrow(/priority must be set for actions added to an imported listener/);
+  });
+
   testDeprecated('Can add redirect responses', () => {
     // GIVEN
     const stack = new cdk.Stack();