feat(ecs): add a service extension interface to ECS services

packages/@aws-cdk/aws-ecs/README.md

@@ -788,3 +788,32 @@ new ecs.FargateService(stack, 'FargateService', {
 
 app.synth();
 ```
+
+## Add Service Extensions
+
+You may create and apply packaged sets of modifications to ECS services by
+implementing one or both of `IFargateServiceExtension` or `IEc2ServiceExtension`
+in your code and by adding the extension to your ECS service.
+
+```ts
+class MyStandardScaling implements ecs.IFargateServiceExtension, ecs.IEc2ServiceExtension {
+  // Compatible with both FargateService and Ec2Service
+  extend(service: ecs.FargateService | ecs.Ec2Service): void {
+    service.autoScaleTaskCount({
+      maxCapacity: 100,
+      minCapacity: 2,
+    }).scaleOnCpuUtilization('Target40', {
+      targetUtilizationPercent: 40,
+    });
+  }
+}
+
+// Create a fargate service
+const fargateService = new ecs.FargateService(...);
+// Apply your neatly packaged modification to the service.
+fargateService.addExtension(new MyStandardScaling());
+
+// Or create an EC2 service and apply it there.
+const ec2Service = new ecs.Ec2Service(...);
+ec2Service.addExtension(new MyStandardScaling());
+```

packages/@aws-cdk/aws-ecs/lib/base/task-definition.ts

@@ -522,7 +522,7 @@ export class TaskDefinition extends TaskDefinitionBase {
   }
 
   /**
-   * Adds the specified extention to the task definition.
+   * Adds the specified extension to the task definition.
    *
    * Extension can be used to apply a packaged modification to
    * a task definition.

packages/@aws-cdk/aws-ecs/lib/ec2/ec2-service.ts

@@ -258,6 +258,16 @@ export class Ec2Service extends BaseService implements IEc2Service {
     }
   }
 
+  /**
+   * Adds the specified extension to the service.
+   *
+   * Extension can be used to apply a packaged modification to
+   * a service.
+   */
+  public addExtension(extension: IEc2ServiceExtension) {
+    extension.extend(this);
+  }
+
   /**
    * Validates this Ec2Service.
    */
@@ -335,3 +345,21 @@ export class BuiltInAttributes {
    */
   public static readonly OS_TYPE = 'attribute:ecs.os-type';
 }
+
+/**
+ * An extension for `FargateService`
+ *
+ * Classes that want to make changes to a FargateService (such as applying a
+ * standard autoscaling pattern) can implement this interface, and can then
+ * be "added" to a service like so:
+ *
+ *    service.addExtension(new MyExtension("some_parameter"));
+ */
+export interface IEc2ServiceExtension {
+  /**
+   * Apply the extension to the given service
+   *
+   * @param service [disable-awslint:ref-via-interface]
+   */
+  extend(service: Ec2Service): void;
+}

packages/@aws-cdk/aws-ecs/lib/fargate/fargate-service.ts

@@ -176,6 +176,16 @@ export class FargateService extends BaseService implements IFargateService {
       validate: () => !this.taskDefinition.defaultContainer ? ['A TaskDefinition must have at least one essential container'] : [],
     });
   }
+
+  /**
+   * Adds the specified extention to the service.
+   *
+   * Extension can be used to apply a packaged modification to
+   * a service.
+   */
+  public addExtension(extension: IFargateServiceExtension) {
+    extension.extend(this);
+  }
 }
 
 /**
@@ -233,3 +243,21 @@ const SECRET_JSON_FIELD_UNSUPPORTED_PLATFORM_VERSIONS = [
   FargatePlatformVersion.VERSION1_2,
   FargatePlatformVersion.VERSION1_3,
 ];
+
+/**
+ * An extension for `FargateService`
+ *
+ * Classes that want to make changes to a FargateService (such as applying a
+ * standard autoscaling pattern) can implement this interface, and can then
+ * be "added" to a service like so:
+ *
+ *    service.addExtension(new MyExtension("some_parameter"));
+ */
+export interface IFargateServiceExtension {
+  /**
+   * Apply the extension to the given service
+   *
+   * @param service [disable-awslint:ref-via-interface]
+   */
+  extend(service: FargateService): void;
+}

packages/@aws-cdk/aws-ecs/test/service-extensions.test.ts

@@ -0,0 +1,84 @@
+import * as cdk from '@aws-cdk/core';
+import * as ecs from '../lib';
+import { expect as expectCDK, haveResource } from '@aws-cdk/assert';
+
+describe('service extensions', () => {
+  test('allows the user to create an extension that works for both ec2 and fargate services', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const cluster = new ecs.Cluster(stack, 'Cluster');
+
+    // A very compatible task definition
+    const taskDefinition = new ecs.TaskDefinition(stack, 'TaskDefinition', {
+      compatibility: ecs.Compatibility.EC2_AND_FARGATE,
+      cpu: '256',
+      memoryMiB: '512',
+    });
+    const mainContainer = taskDefinition.addContainer('main', {
+      image: ecs.ContainerImage.fromRegistry('nginx'),
+      memoryLimitMiB: 512,
+    });
+    mainContainer.addPortMappings({ containerPort: 80 });
+
+    // A very compatible service extension
+    class MyStandardScaling implements ecs.IFargateServiceExtension, ecs.IEc2ServiceExtension {
+      extend(s: ecs.FargateService | ecs.Ec2Service): void {
+        s.autoScaleTaskCount({
+          maxCapacity: 100,
+          minCapacity: 2,
+        }).scaleOnCpuUtilization('Target40', {
+          targetUtilizationPercent: 40,
+        });
+      }
+    }
+
+    const myStandardScalingExtension = new MyStandardScaling();
+    const extendSpy = jest.spyOn(myStandardScalingExtension, 'extend');
+
+    const fargateService = new ecs.FargateService(stack, 'FargateService', {
+      cluster,
+      taskDefinition,
+    });
+
+    const ec2Service = new ecs.FargateService(stack, 'Ec2Service', {
+      cluster,
+      taskDefinition,
+    });
+
+    // WHEN
+    fargateService.addExtension(myStandardScalingExtension);
+    ec2Service.addExtension(myStandardScalingExtension);
+
+    // THEN
+    expect(extendSpy).toBeCalledWith(fargateService);
+    expect(extendSpy).toBeCalledWith(ec2Service);
+
+    expectCDK(stack).to(haveResource('AWS::ApplicationAutoScaling::ScalableTarget', {
+      ResourceId: {
+        'Fn::Join': [
+          '',
+          [
+            'service/',
+            { Ref: 'ClusterEB0386A7' },
+            '/',
+            { 'Fn::GetAtt': ['FargateServiceAC2B3B85', 'Name'] },
+          ],
+        ],
+      },
+    }));
+
+    expectCDK(stack).to(haveResource('AWS::ApplicationAutoScaling::ScalableTarget', {
+      ResourceId: {
+        'Fn::Join': [
+          '',
+          [
+            'service/',
+            { Ref: 'ClusterEB0386A7' },
+            '/',
+            { 'Fn::GetAtt': ['Ec2Service04A33183', 'Name'] },
+          ],
+        ],
+      },
+    }));
+  });
+});