fix(aws-ecs): allow empty placementStrategies on EC2Service

Same fix as #30382 but for `placementStrategies`. Apparently this was
not done at that time because CloudFormation [previously did not have
the appropriate
semantics](#27572 (comment))
for setting PlacementStrategies to the empty array as it did for
PlacementConstraints, but that is no longer the case. The CloudFormation
docs
[state](https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-resource-ecs-service.html#cfn-ecs-service-placementstrategies):
> To remove this property from your service resource, specify an empty PlacementStrategy array.

And indeed that works, with this CDK change applied.

Author: isker

packages/@aws-cdk-testing/framework-integ/test/aws-ecs/test/ec2/integ.placement-strategies.js.snapshot/aws-cdk-ecs-integration-test-stack.assets.json

@@ -968,6 +968,28 @@
    "DependsOn": [
     "TaskDefTaskRole1EDB4A67"
    ]
+  },
+  "TestEmptyService1DB8D95A": {
+   "Type": "AWS::ECS::Service",
+   "Properties": {
+    "Cluster": {
+     "Ref": "EcsCluster97242B84"
+    },
+    "DeploymentConfiguration": {
+     "MaximumPercent": 200,
+     "MinimumHealthyPercent": 50
+    },
+    "EnableECSManagedTags": false,
+    "LaunchType": "EC2",
+    "PlacementStrategies": [],
+    "SchedulingStrategy": "REPLICA",
+    "TaskDefinition": {
+     "Ref": "TaskDef54694570"
+    }
+   },
+   "DependsOn": [
+    "TaskDefTaskRole1EDB4A67"
+   ]
   }
  },
  "Parameters": {

packages/@aws-cdk-testing/framework-integ/test/aws-ecs/test/ec2/integ.placement-strategies.js.snapshot/aws-cdk-ecs-integration-test-stack.template.json

@@ -37,6 +37,12 @@ class EcsStack extends cdk.Stack {
         ecs.PlacementStrategy.packedByMemory(),
       ],
     });
+
+    new ecs.Ec2Service(this, 'Test_Empty', {
+      cluster,
+      taskDefinition,
+      placementStrategies: [],
+    });
   }
 }
 

packages/@aws-cdk-testing/framework-integ/test/aws-ecs/test/ec2/integ.placement-strategies.js.snapshot/cdk.out

@@ -163,7 +163,7 @@ export class Ec2Service extends BaseService implements IEc2Service {
   }
 
   private constraints?: CfnService.PlacementConstraintProperty[];
-  private readonly strategies: CfnService.PlacementStrategyProperty[];
+  private strategies?: CfnService.PlacementStrategyProperty[];
   private readonly daemon: boolean;
   private readonly availabilityZoneRebalancingEnabled: boolean;
 
@@ -212,15 +212,13 @@ export class Ec2Service extends BaseService implements IEc2Service {
       cluster: props.cluster.clusterName,
       taskDefinition: props.deploymentController?.type === DeploymentControllerType.EXTERNAL ? undefined : props.taskDefinition.taskDefinitionArn,
       placementConstraints: Lazy.any({ produce: () => this.constraints }),
-      placementStrategies: Lazy.any({ produce: () => this.strategies }, { omitEmptyArray: true }),
+      placementStrategies: Lazy.any({ produce: () => this.strategies }),
       schedulingStrategy: props.daemon ? 'DAEMON' : 'REPLICA',
       availabilityZoneRebalancing: props.availabilityZoneRebalancing,
     }, props.taskDefinition);
     // Enhanced CDK Analytics Telemetry
     addConstructMetadata(this, props);
 
-    this.constraints = undefined;
-    this.strategies = [];
     this.daemon = props.daemon || false;
     this.availabilityZoneRebalancingEnabled = props.availabilityZoneRebalancing === AvailabilityZoneRebalancing.ENABLED;
 
@@ -249,7 +247,9 @@ export class Ec2Service extends BaseService implements IEc2Service {
     if (props.placementConstraints) {
       this.addPlacementConstraints(...props.placementConstraints);
     }
-    this.addPlacementStrategies(...props.placementStrategies || []);
+    if (props.placementStrategies) {
+      this.addPlacementStrategies(...props.placementStrategies);
+    }
 
     this.node.addValidation({
       validate: () => !this.taskDefinition.defaultContainer ? ['A TaskDefinition must have at least one essential container'] : [],
@@ -272,13 +272,14 @@ export class Ec2Service extends BaseService implements IEc2Service {
       throw new ValidationError("Can't configure placement strategies when daemon=true", this);
     }
 
-    if (strategies.length > 0 && this.strategies.length === 0 && this.availabilityZoneRebalancingEnabled) {
+    if (strategies.length > 0 && !this.strategies && this.availabilityZoneRebalancingEnabled) {
       const [placement] = strategies[0].toJson();
       if (placement.type !== 'spread' || placement.field !== BuiltInAttributes.AVAILABILITY_ZONE) {
         throw new ValidationError(`AvailabilityZoneBalancing.ENABLED requires that the first placement strategy, if any, be 'spread across "${BuiltInAttributes.AVAILABILITY_ZONE}"'`, this);
       }
     }
 
+    this.strategies = [];
     for (const strategy of strategies) {
       this.strategies.push(...strategy.toJson());
     }

packages/@aws-cdk-testing/framework-integ/test/aws-ecs/test/ec2/integ.placement-strategies.js.snapshot/integ.json

@@ -2307,6 +2307,31 @@ describe('ec2 service', () => {
       });
     });
 
+    test('with empty [] placement strategies', () => {
+      // GIVEN
+      const stack = new cdk.Stack();
+      const vpc = new ec2.Vpc(stack, 'MyVpc', {});
+      const cluster = new ecs.Cluster(stack, 'EcsCluster', { vpc });
+      addDefaultCapacityProvider(cluster, stack, vpc);
+      const taskDefinition = new ecs.Ec2TaskDefinition(stack, 'Ec2TaskDef');
+
+      taskDefinition.addContainer('web', {
+        image: ecs.ContainerImage.fromRegistry('amazon/amazon-ecs-sample'),
+        memoryLimitMiB: 512,
+      });
+
+      new ecs.Ec2Service(stack, 'Ec2Service', {
+        cluster,
+        taskDefinition,
+        placementStrategies: [],
+      });
+
+      // THEN
+      Template.fromStack(stack).hasResourceProperties('AWS::ECS::Service', {
+        PlacementStrategies: Match.arrayEquals([]),
+      });
+    });
+
     testDeprecated('with both propagateTags and propagateTaskTagsFrom defined', () => {
       // GIVEN
       const stack = new cdk.Stack();