fix(ecs): new arn format not supported (under feature flag) (aws#18140)

AWS has changed the [ARN format for ECS](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-account-settings.html#ecs-resource-ids). Currently, CDK doesn't return the correct values/ARNs if the new ARN format is used in ECS.

Changed methods:
- `Ec2Service.fromEc2ServiceAttributes()`
- `Ec2Service.fromEc2ServiceArn()`
- `FargateService.fromFargateServiceAttributes()`
- `FargateService.fromFargateServiceArn()`

The logic automatically detects whether the old or new format is used. The format cannot be recognized automatically for tokenized values. Therefore the feature flag `ECS_ARN_FORMAT_INCLUDES_CLUSTER_NAME` is introduced, which controls whether the old or the new format should be used.

In `Ec2Service.fromEc2ServiceAttributes()` and `FargateService.fromFargateServiceAttributes()` an ARN is created. In these methods the feature flag be considered to construct the ARN in the correct format.

Closes aws#16634.
Closes aws#18137.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

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

@@ -703,6 +703,37 @@ There are two higher-level constructs available which include a load balancer fo
 - `LoadBalancedFargateService`
 - `LoadBalancedEc2Service`
 
+### Import existing services
+
+`Ec2Service` and `FargateService` provide methods to import existing EC2/Fargate services.
+The ARN of the existing service has to be specified to import the service.
+
+Since AWS has changed the [ARN format for ECS](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-account-settings.html#ecs-resource-ids), 
+feature flag `@aws-cdk/aws-ecs:arnFormatIncludesClusterName` must be enabled to use the new ARN format.
+The feature flag changes behavior for the entire CDK project. Therefore it is not possible to mix the old and the new format in one CDK project.
+
+```tss
+declare const cluster: ecs.Cluster;
+
+// Import service from EC2 service attributes
+const service = ecs.Ec2Service.fromEc2ServiceAttributes(stack, 'EcsService', {
+  serviceArn: 'arn:aws:ecs:us-west-2:123456789012:service/my-http-service',
+  cluster,
+});
+
+// Import service from EC2 service ARN
+const service = ecs.Ec2Service.fromEc2ServiceArn(stack, 'EcsService', 'arn:aws:ecs:us-west-2:123456789012:service/my-http-service');
+
+// Import service from Fargate service attributes
+const service = ecs.FargateService.fromFargateServiceAttributes(stack, 'EcsService', {
+  serviceArn: 'arn:aws:ecs:us-west-2:123456789012:service/my-http-service',
+  cluster,
+});
+
+// Import service from Fargate service ARN
+const service = ecs.FargateService.fromFargateServiceArn(stack, 'EcsService', 'arn:aws:ecs:us-west-2:123456789012:service/my-http-service');
+```
+
 ## Task Auto-Scaling
 
 You can configure the task count of a service to match demand. Task auto-scaling is

packages/@aws-cdk/aws-ecs/lib/base/from-service-attributes.ts

@@ -1,4 +1,5 @@
-import { ArnFormat, Resource, Stack } from '@aws-cdk/core';
+import { ArnFormat, FeatureFlags, Fn, Resource, Stack, Token } from '@aws-cdk/core';
+import { ECS_ARN_FORMAT_INCLUDES_CLUSTER_NAME } from '@aws-cdk/cx-api';
 import { Construct } from 'constructs';
 import { IBaseService } from '../base/base-service';
 import { ICluster } from '../cluster';
@@ -32,22 +33,25 @@ export function fromServiceAttributes(scope: Construct, id: string, attrs: Servi
     throw new Error('You can only specify either serviceArn or serviceName.');
   }
 
+  const newArnFormat = FeatureFlags.of(scope).isEnabled(ECS_ARN_FORMAT_INCLUDES_CLUSTER_NAME);
+
   const stack = Stack.of(scope);
   let name: string;
   let arn: string;
   if (attrs.serviceName) {
     name = attrs.serviceName as string;
+    const resourceName = newArnFormat ? `${attrs.cluster.clusterName}/${attrs.serviceName}` : attrs.serviceName as string;
     arn = stack.formatArn({
       partition: stack.partition,
       service: 'ecs',
       region: stack.region,
       account: stack.account,
       resource: 'service',
-      resourceName: name,
+      resourceName,
     });
   } else {
     arn = attrs.serviceArn as string;
-    name = stack.splitArn(arn, ArnFormat.SLASH_RESOURCE_NAME).resourceName as string;
+    name = extractServiceNameFromArn(scope, arn);
   }
   class Import extends Resource implements IBaseService {
     public readonly serviceArn = arn;
@@ -58,3 +62,22 @@ export function fromServiceAttributes(scope: Construct, id: string, attrs: Servi
     environmentFromArn: arn,
   });
 }
+
+export function extractServiceNameFromArn(scope: Construct, arn: string): string {
+  const newArnFormat = FeatureFlags.of(scope).isEnabled(ECS_ARN_FORMAT_INCLUDES_CLUSTER_NAME);
+  const stack = Stack.of(scope);
+
+  if (Token.isUnresolved(arn)) {
+    if (newArnFormat) {
+      const components = Fn.split(':', arn);
+      const lastComponents = Fn.split('/', Fn.select(5, components));
+      return Fn.select(2, lastComponents);
+    } else {
+      return stack.splitArn(arn, ArnFormat.SLASH_RESOURCE_NAME).resourceName as string;
+    }
+  } else {
+    const resourceName = stack.splitArn(arn, ArnFormat.SLASH_RESOURCE_NAME).resourceName as string;
+    const resourceNameSplit = resourceName.split('/');
+    return resourceNameSplit.length === 1 ? resourceName : resourceNameSplit[1];
+  }
+}

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

@@ -1,8 +1,8 @@
 import * as ec2 from '@aws-cdk/aws-ec2';
-import { ArnFormat, Lazy, Resource, Stack } from '@aws-cdk/core';
+import { Lazy, Resource, Stack } from '@aws-cdk/core';
 import { Construct } from 'constructs';
 import { BaseService, BaseServiceOptions, DeploymentControllerType, IBaseService, IService, LaunchType } from '../base/base-service';
-import { fromServiceAttributes } from '../base/from-service-attributes';
+import { fromServiceAttributes, extractServiceNameFromArn } from '../base/from-service-attributes';
 import { NetworkMode, TaskDefinition } from '../base/task-definition';
 import { ICluster } from '../cluster';
 import { CfnService } from '../ecs.generated';
@@ -128,7 +128,7 @@ export class Ec2Service extends BaseService implements IEc2Service {
   public static fromEc2ServiceArn(scope: Construct, id: string, ec2ServiceArn: string): IEc2Service {
     class Import extends Resource implements IEc2Service {
       public readonly serviceArn = ec2ServiceArn;
-      public readonly serviceName = Stack.of(scope).splitArn(ec2ServiceArn, ArnFormat.SLASH_RESOURCE_NAME).resourceName as string;
+      public readonly serviceName = extractServiceNameFromArn(this, ec2ServiceArn);
     }
     return new Import(scope, id);
   }

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

@@ -1,9 +1,8 @@
 import * as ec2 from '@aws-cdk/aws-ec2';
 import * as cdk from '@aws-cdk/core';
-import { ArnFormat } from '@aws-cdk/core';
 import { Construct } from 'constructs';
 import { BaseService, BaseServiceOptions, DeploymentControllerType, IBaseService, IService, LaunchType } from '../base/base-service';
-import { fromServiceAttributes } from '../base/from-service-attributes';
+import { fromServiceAttributes, extractServiceNameFromArn } from '../base/from-service-attributes';
 import { TaskDefinition } from '../base/task-definition';
 import { ICluster } from '../cluster';
 
@@ -105,7 +104,7 @@ export class FargateService extends BaseService implements IFargateService {
   public static fromFargateServiceArn(scope: Construct, id: string, fargateServiceArn: string): IFargateService {
     class Import extends cdk.Resource implements IFargateService {
       public readonly serviceArn = fargateServiceArn;
-      public readonly serviceName = cdk.Stack.of(scope).splitArn(fargateServiceArn, ArnFormat.SLASH_RESOURCE_NAME).resourceName as string;
+      public readonly serviceName = extractServiceNameFromArn(this, fargateServiceArn);
     }
     return new Import(scope, id);
   }