feat(ecs-service-extensions): create an Environment from attributes

packages/@aws-cdk-containers/ecs-service-extensions/README.md

@@ -283,3 +283,20 @@ 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.
+
+## Importing a pre-existing cluster
+
+To create an environment with a pre-existing cluster, you must import the cluster first, then use `Environment.fromEnvironmentAttributes()`. When a cluster is imported into an environment, the cluster is treated as immutable. As a result, no extension may modify the cluster to change a setting.
+
+```ts
+
+const cluster = ecs.Cluster.fromClusterAttributes(stack, 'Cluster', {
+  ...
+});
+
+const environment = Environment.fromEnvironmentAttributes(stack, 'Environment', {
+  capacityType: EnvironmentCapacityType.EC2, // or `FARGATE`
+  cluster,
+});
+
+```

packages/@aws-cdk-containers/ecs-service-extensions/lib/environment.ts

@@ -28,13 +28,50 @@ export interface EnvironmentProps {
   readonly capacityType?: EnvironmentCapacityType
 }
 
+/**
+ * An environment into which to deploy a service.
+ */
+export interface IEnvironment {
+  /**
+   * The name of this environment.
+   */
+  readonly id: string;
+
+  /**
+   * The VPC into which environment services should be placed.
+   */
+  readonly vpc: ec2.IVpc;
+
+  /**
+   * The cluster that is providing capacity for this service.
+   */
+  readonly cluster: ecs.ICluster;
+
+  /**
+   * The capacity type used by the service's cluster.
+   */
+  readonly capacityType: EnvironmentCapacityType;
+
+  /**
+   * Add a default cloudmap namespace to the environment's cluster.
+   */
+  addDefaultCloudMapNamespace(options: ecs.CloudMapNamespaceOptions): void;
+}
+
 /**
  * An environment into which to deploy a service. This environment
  * can either be instantiated with a preexisting AWS VPC and ECS cluster,
  * or it can create it's own VPC and cluster. By default it will create
  * a cluster with Fargate capacity.
  */
-export class Environment extends cdk.Construct {
+export class Environment extends cdk.Construct implements IEnvironment {
+  /**
+   * Import an existing environment from its attributes.
+   */
+  public static fromEnvironmentAttributes(scope: cdk.Construct, id: string, attrs: EnvironmentAttributes): IEnvironment {
+    return new ImportedEnvironment(scope, id, attrs);
+  }
+
   /**
    * The name of this environment.
    */
@@ -81,4 +118,47 @@ export class Environment extends cdk.Construct {
       this.capacityType = EnvironmentCapacityType.FARGATE;
     }
   }
+
+  /**
+   * Add a default cloudmap namespace to the environment's cluster.
+   */
+  addDefaultCloudMapNamespace(options: ecs.CloudMapNamespaceOptions) {
+    this.cluster.addDefaultCloudMapNamespace(options);
+  }
+}
+
+export interface EnvironmentAttributes {
+  /**
+   * The capacity type used by the service's cluster.
+   */
+  capacityType: EnvironmentCapacityType;
+
+  /**
+   * The cluster that is providing capacity for this service.
+   */
+  cluster: ecs.ICluster;
 }
+
+export class ImportedEnvironment extends cdk.Construct implements IEnvironment {
+  public readonly capacityType: EnvironmentCapacityType;
+  public readonly cluster: ecs.ICluster;
+  public readonly id: string;
+  public readonly vpc: ec2.IVpc;
+
+  constructor(scope: cdk.Construct, id: string, props: EnvironmentAttributes) {
+    super(scope, id);
+
+    this.id = id;
+    this.capacityType = props.capacityType;
+    this.cluster = props.cluster;
+    this.vpc = props.cluster.vpc;
+  }
+
+  /**
+   * Refuses to add a default cloudmap namespace to the cluster as we don't
+   * own it.
+   */
+  addDefaultCloudMapNamespace(_options: ecs.CloudMapNamespaceOptions) {
+    throw new Error('the cluster environment is immutable when imported');
+  }
+}

packages/@aws-cdk-containers/ecs-service-extensions/lib/extensions/appmesh.ts

@@ -70,7 +70,7 @@ export class AppMeshExtension extends ServiceExtension {
     // Make sure that the parent cluster for this service has
     // a namespace attached.
     if (!this.parentService.cluster.defaultCloudMapNamespace) {
-      this.parentService.cluster.addDefaultCloudMapNamespace({
+      this.parentService.environment.addDefaultCloudMapNamespace({
         // Name the namespace after the environment name.
         // Service DNS will be like <service id>.<environment id>
         name: this.parentService.environment.id,

packages/@aws-cdk-containers/ecs-service-extensions/lib/service.ts

@@ -1,7 +1,7 @@
 import * as ec2 from '@aws-cdk/aws-ec2';
 import * as ecs from '@aws-cdk/aws-ecs';
 import * as cdk from '@aws-cdk/core';
-import { Environment } from './environment';
+import { IEnvironment } from './environment';
 import { EnvironmentCapacityType, ServiceBuild } from './extensions/extension-interfaces';
 import { ServiceDescription } from './service-description';
 
@@ -17,7 +17,7 @@ export interface ServiceProps {
   /**
    * The environment to launch the service in
    */
-  readonly environment: Environment
+  readonly environment: IEnvironment
 }
 
 /**
@@ -44,7 +44,7 @@ export class Service extends cdk.Construct {
    * The cluster that is providing capacity for this service
    * [disable-awslint:ref-via-interface]
    */
-  public readonly cluster: ecs.Cluster;
+  public readonly cluster: ecs.ICluster;
 
   /**
    * The capacity type that this service will use
@@ -59,7 +59,7 @@ export class Service extends cdk.Construct {
   /**
    * The environment this service was launched in
    */
-  public readonly environment: Environment;
+  public readonly environment: IEnvironment;
 
   /**
    * The generated task definition for this service, is only