@aws-cdk-containers/ecs-service-extensions

CDK Construct library for building ECS services

---

The APIs of higher level constructs in this module are experimental and under active development. They are subject to non-backward compatible changes or removal in any future version. These are not subject to the Semantic Versioning model and breaking changes will be announced in the release notes. This means that while you may use them, you may need to update your source code when upgrading to a newer version of this package.

---

This library provides a high level, extensible pattern for constructing services deployed using Amazon ECS.

The Service construct provided by this module can be extended with optional ServiceExtension classes that add supplemental ECS features including:

• AWS X-Ray for tracing your application
• Amazon CloudWatch Agent for capturing per task stats
• AWS AppMesh for adding your application to a service mesh
• Application Load Balancer, for exposing your service to the public
• AWS FireLens, for filtering and routing application logs

The ServiceExtension class is an abstract class which you can also implement in order to build your own custom service extensions for modifying your service, or attaching your own custom resources or sidecars.

Example

import { AppMeshExtension, CloudwatchAgentExtension, Container, Environment, FireLensExtension, HttpLoadBalancerExtension, Service, ServiceDescription, XRayExtension } from 'ecs-service-builder';

// Create an environment to deploy a service in.
const environment = new Environment(stack, 'production');

// Build out the service description
const nameDescription = new ServiceDescription();
nameDescription.add(new Container({
  cpu: 1024,
  memoryMiB: 2048,
  trafficPort: 80,
  image: ContainerImage.fromRegistry('nathanpeck/name'),
  environment: {
    PORT: '80',
  },
}));
nameDescription.add(new AppMeshExtension({ mesh }));
nameDescription.add(new FireLensExtension());
nameDescription.add(new XRayExtension());
nameDescription.add(new CloudwatchAgentExtension());
nameDescription.add(new HttpLoadBalancerExtension());

// Implement the service description as a real service inside
// an environment.
const nameService = new Service(stack, 'name', {
  environment: environment,
  serviceDescription: nameDescription,
});

Creating an Environment

An Environment is a place to deploy your services. You can have multiple environments on a single AWS account. For example you could create a test environment as well as a production environment so you have a place to verify that you application works as intended before you deploy it to a live environment.

Each environment is isolated from other environments. In specific by default when you create an environment the construct supplies its own VPC, ECS Cluster, and any other required resources for the environment:

const environment = new Environment(stack, 'production');

However, you can also choose to build an environment out of a pre-existing VPC, or ECS Cluster:

const vpc = new ec2.Vpc(stack, 'VPC');
const cluster = new ecs.Cluster(stack, 'Cluster', { vpc });

const environment = new Environment(stack, 'production', {
  vpc,
  cluster,
});

Defining your ServiceDescription

The ServiceDescription defines what application you want the service to run and what optional extensions you want to add to the service. The most basic form of a ServiceExtension looks like this:

const nameDescription = new ServiceDescription();
nameDescription.add(new Container({
  cpu: 1024,
  memoryMiB: 2048,
  trafficPort: 80,
  image: ContainerImage.fromRegistry('nathanpeck/name'),
  environment: {
    PORT: '80',
  },
}));

Every ServiceDescription requires at minimum that you add a Container extension which defines the main application container to run for the service.

After that you can optionally enable additional features for the service using the ServiceDescription.add() method:

nameDescription.add(new AppMeshExtension({ mesh }));
nameDescription.add(new FireLensExtension());
nameDescription.add(new XRayExtension());
nameDescription.add(new CloudwatchAgentExtension());
nameDescription.add(new HttpLoadBalancerExtension());

Launching the ServiceDescription as a Service

Once the service description is defined, you can launch it as a service:

const nameService = new Service(stack, 'name', {
  environment: environment,
  serviceDescription: nameDescription,
});

At this point, all the service resources will be created. This includes the ECS Task Definition, Service, as well as any other attached resources, such as App Mesh Virtual Node or an Application Load Balancer.

Creating your own custom ServiceExtension

In addition to using the default service extensions that come with this module, you can choose to implement your own custom service extensions. The ServiceExtension class is an abstract class you can implement yourself. The following example implements a custom service extension that could be added to a service in order to autoscale it based on CPU:

export class MyCustomAutoscaling extends ServiceExtension {
  constructor() {
    super('my-custom-autoscaling');
  }

  // This function modifies properties of the service prior
  // to construct creation.
  public modifyServiceProps(props: ServiceBuild) {
    return {
      ...props,

      // Initially launch 10 copies of the service
      desiredCount: 10
    } as ServiceBuild;
  }

  // This hook utilizes the resulting service construct
  // once it is created
  public useService(service: ecs.Ec2Service | ecs.FargateService) {
    const scalingTarget = service.autoScaleTaskCount({
      minCapacity: 5, // Min 5 tasks
      maxCapacity: 20 // Max 20 tasks
    });

    scalingTarget.scaleOnCpuUtilization('TargetCpuUtilization50', {
      targetUtilizationPercent: 50,
      scaleInCooldown: cdk.Duration.seconds(60),
      scaleOutCooldown: cdk.Duration.seconds(60),
    });
  }
}

This ServiceExtension can now be reused and added to any number of different service descriptions. This allows you to develop reusable bits of configuration, attach them to many different services, and centrally manage them. Updating the ServiceExtension in one place would update all services that use it, instead of requiring decentralized updates to many different services.

Every ServiceExtension can implement the following hooks to modify the properties of constructs, or make use of the resulting constructs:

• addHooks() - This hook is called after all the extensions are added to a ServiceDescription, but before any of the other extension hooks have been run. It gives each extension a chance to do some inspection of the overall ServiceDescription and see what other extensions have been added. Some extensions may want to register hooks on the other extensions to modify them. For example, the Firelens extension wants to be able to modify the settings of the application container to route logs through Firelens.
• modifyTaskDefinitionProps() - This is hook is passed the proposed ecs.TaskDefinitionProps for a TaskDefinition that is about to be created. This allows the extension to make modifications to the task definition props before the TaskDefinition is created. For example, the App Mesh extension modifies the proxy settings for the task.
• useTaskDefinition() - After the TaskDefinition is created, this hook is passed the actual TaskDefinition construct that was created. This allows the extension to add containers to the task, modify the task definition's IAM role, etc.
• resolveContainerDependencies() - Once all extensions have added their containers, each extension is given a chance to modify its container's dependsOn settings. Extensions need to check and see what other extensions were enabled and decide whether their container needs to wait on another container to start first.
• modifyServiceProps() - Before an Ec2Service or FargateService is created, this hook is passed a draft version of the service props to change. Each extension adds its own modifications to the service properties. For example, the App Mesh extension needs to modify the service settings to enable CloudMap service discovery.
• useService() - After the service is created, this hook is given a chance to utilize that service. This is used by extensions like the load balancer or App Mesh extension, which create and link other AWS resources to the ECS extension.
• connectToService() - This hook is called when a user wants to connect one service to another service. It allows an extension to implement logic about how to allow connections from one service to another. For example, the App Mesh extension implements this method in order to easily connect one service mesh service to another, which allows the service's Envoy proxy sidecars to route traffic to each other.

Connecting services

One of the hooks that a ServiceExtension can implement is a hook for connection logic. This is utilized when connecting one service to another service, e.g. connecting a user facing web service with a backend API. Usage looks like this:

const frontend = new Service(stack, 'frontend', {
  environment,
  serviceDescription: frontendDescription
});
const backend = new Service(stack, 'backend', {
  environment,
  serviceDescription: backendDescription
});

frontend.connectTo(backend);

The address that a service will use to talk to another service depends on the type of ingress that has been created by the extension that did the connecting. For example if an App Mesh extension has been used then the service is accessible at a DNS address of <service name>.<environment name>. For example:

const environment = new Environment(stack, 'production');

// Define the frontend tier
const frontendDescription = new ServiceDescription();
frontendDescription.add(new Container({
  cpu: 1024,
  memoryMiB: 2048,
  trafficPort: 80,
  image: ContainerImage.fromRegistry('my-frontend-service'),
  environment: {
    BACKEND_URL: 'http://backend.production'
  },
}));
const frontend = new Service(stack, 'frontend', {
  environment,
  serviceDescription: frontendDescription
});

// Define the backend tier
const backendDescription = new ServiceDescription();
backendDescription.add(new Container({
  cpu: 1024,
  memoryMiB: 2048,
  trafficPort: 80,
  image: ContainerImage.fromRegistry('my-backend-service'),
  environment: {
    FRONTEND_URL: 'http://frontend.production'
  },
}));
const backend = new Service(stack, 'backend', {
  environment,
  serviceDescription: backendDescription
});

// Connect the two tiers to each other
frontend.connectTo(backend);

The above code uses the well known service discovery name for each service, and passes it as an environment variable to the container so that the container knows what address to use when communicating to the other service.