fix(ecs-patterns): handle desired task count being set to 0

packages/@aws-cdk/aws-ecs-patterns/lib/base/application-load-balanced-service-base.ts

@@ -43,6 +43,7 @@ export interface ApplicationLoadBalancedServiceBaseProps {
 
   /**
    * The desired number of instantiations of the task definition to keep running on the service.
+   * The minimum value is 1
    *
    * @default 1
    */
@@ -258,6 +259,9 @@ export abstract class ApplicationLoadBalancedServiceBase extends cdk.Construct {
     }
     this.cluster = props.cluster || this.getDefaultCluster(this, props.vpc);
 
+    if (props.desiredCount !== undefined && props.desiredCount < 1) {
+      throw new Error('You must specify a desiredCount greater than 0');
+    }
     this.desiredCount = props.desiredCount || 1;
 
     const internetFacing = props.publicLoadBalancer !== undefined ? props.publicLoadBalancer : true;

packages/@aws-cdk/aws-ecs-patterns/lib/base/network-load-balanced-service-base.ts

@@ -42,6 +42,7 @@ export interface NetworkLoadBalancedServiceBaseProps {
 
   /**
    * The desired number of instantiations of the task definition to keep running on the service.
+   * The minimum value is 1
    *
    * @default 1
    */
@@ -230,6 +231,9 @@ export abstract class NetworkLoadBalancedServiceBase extends cdk.Construct {
     }
     this.cluster = props.cluster || this.getDefaultCluster(this, props.vpc);
 
+    if (props.desiredCount !== undefined && props.desiredCount < 1) {
+      throw new Error('You must specify a desiredCount greater than 0');
+    }
     this.desiredCount = props.desiredCount || 1;
 
     const internetFacing = props.publicLoadBalancer !== undefined ? props.publicLoadBalancer : true;

packages/@aws-cdk/aws-ecs-patterns/lib/base/queue-processing-service-base.ts

@@ -211,9 +211,13 @@ export abstract class QueueProcessingServiceBase extends Construct {
     this.secrets = props.secrets;
 
     // Determine the desired task count (minimum) and maximum scaling capacity
-    this.desiredCount = props.desiredTaskCount || 1;
+    this.desiredCount = props.desiredTaskCount !== undefined ? props.desiredTaskCount : 1;
     this.maxCapacity = props.maxScalingCapacity || (2 * this.desiredCount);
 
+    if (!this.desiredCount && !this.maxCapacity) {
+      throw new Error(`maxScalingCapacity must be set and greater than 0 if desiredCount is 0`);
+    }
+
     new CfnOutput(this, 'SQSQueue', { value: this.sqsQueue.queueName });
     new CfnOutput(this, 'SQSQueueArn', { value: this.sqsQueue.queueArn });
   }

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

@@ -90,6 +90,8 @@ export abstract class ScheduledTaskBase extends Construct {
   public readonly cluster: ICluster;
   /**
    * The desired number of instantiations of the task definition to keep running on the service.
+   *
+   * The minimum value is 1
    */
   public readonly desiredTaskCount: number;
 
@@ -105,6 +107,9 @@ export abstract class ScheduledTaskBase extends Construct {
     super(scope, id);
 
     this.cluster = props.cluster || this.getDefaultCluster(this, props.vpc);
+    if (props.desiredTaskCount !== undefined && props.desiredTaskCount < 1) {
+      throw new Error('You must specify a desiredTaskCount greater than 0');
+    }
     this.desiredTaskCount = props.desiredTaskCount || 1;
 
     // An EventRule that describes the event trigger (in this case a scheduled run)

packages/@aws-cdk/aws-ecs-patterns/test/ec2/test.l3s.ts

@@ -729,4 +729,48 @@ export = {
 
     test.done();
   },
+
+  'ALB - throws if desiredTaskCount is 0'(test: Test) {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'VPC');
+    const cluster = new ecs.Cluster(stack, 'Cluster', { vpc });
+    cluster.addCapacity('DefaultAutoScalingGroup', { instanceType: new ec2.InstanceType('t2.micro') });
+
+    // THEN
+    test.throws(() =>
+      new ecsPatterns.ApplicationLoadBalancedEc2Service(stack, 'Service', {
+        cluster,
+        memoryLimitMiB: 1024,
+        taskImageOptions: {
+          image: ecs.ContainerImage.fromRegistry('test'),
+        },
+        desiredCount: 0,
+      })
+    , /You must specify a desiredCount greater than 0/);
+
+    test.done();
+  },
+
+  'NLB - throws if desiredTaskCount is 0'(test: Test) {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'VPC');
+    const cluster = new ecs.Cluster(stack, 'Cluster', { vpc });
+    cluster.addCapacity('DefaultAutoScalingGroup', { instanceType: new ec2.InstanceType('t2.micro') });
+
+    // THEN
+    test.throws(() =>
+      new ecsPatterns.NetworkLoadBalancedEc2Service(stack, 'Service', {
+        cluster,
+        memoryLimitMiB: 1024,
+        taskImageOptions: {
+          image: ecs.ContainerImage.fromRegistry('test'),
+        },
+        desiredCount: 0,
+      })
+    , /You must specify a desiredCount greater than 0/);
+
+    test.done();
+  },
 };

packages/@aws-cdk/aws-ecs-patterns/test/ec2/test.queue-processing-ecs-service.ts

@@ -140,5 +140,50 @@ export = {
     }));
 
     test.done();
-  }
+  },
+
+  'can set desiredTaskCount to 0'(test: Test) {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'VPC');
+    const cluster = new ecs.Cluster(stack, 'Cluster', { vpc });
+    cluster.addCapacity('DefaultAutoScalingGroup', { instanceType: new ec2.InstanceType('t2.micro') });
+
+    // WHEN
+    new ecsPatterns.QueueProcessingEc2Service(stack, 'Service', {
+      cluster,
+      desiredTaskCount: 0,
+      maxScalingCapacity: 2,
+      memoryLimitMiB: 512,
+      image: ecs.ContainerImage.fromRegistry('test')
+    });
+
+    // THEN - QueueWorker is of EC2 launch type, an SQS queue is created and all default properties are set.
+    expect(stack).to(haveResource("AWS::ECS::Service", {
+      DesiredCount: 0,
+      LaunchType: "EC2",
+    }));
+
+    test.done();
+  },
+
+  'throws if desiredTaskCount and maxScalingCapacity are 0'(test: Test) {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'VPC');
+    const cluster = new ecs.Cluster(stack, 'Cluster', { vpc });
+    cluster.addCapacity('DefaultAutoScalingGroup', { instanceType: new ec2.InstanceType('t2.micro') });
+
+    // THEN
+    test.throws(() =>
+      new ecsPatterns.QueueProcessingEc2Service(stack, 'Service', {
+        cluster,
+        desiredTaskCount: 0,
+        memoryLimitMiB: 512,
+        image: ecs.ContainerImage.fromRegistry('test')
+      })
+    , /maxScalingCapacity must be set and greater than 0 if desiredCount is 0/);
+
+    test.done();
+  },
 };

packages/@aws-cdk/aws-ecs-patterns/test/ec2/test.scheduled-ecs-task.ts

@@ -232,4 +232,29 @@ export = {
 
     test.done();
   },
+
+  "throws if desiredTaskCount is 0"(test: Test) {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'Vpc', { maxAzs: 1 });
+    const cluster = new ecs.Cluster(stack, 'EcsCluster', { vpc });
+    cluster.addCapacity('DefaultAutoScalingGroup', {
+      instanceType: new ec2.InstanceType('t2.micro')
+    });
+
+    // THEN
+    test.throws(() =>
+      new ScheduledEc2Task(stack, 'ScheduledEc2Task', {
+        cluster,
+        scheduledEc2TaskImageOptions: {
+          image: ecs.ContainerImage.fromRegistry('henk'),
+          memoryLimitMiB: 512,
+        },
+        schedule: events.Schedule.expression('rate(1 minute)'),
+        desiredTaskCount: 0,
+      }),
+    /You must specify a desiredTaskCount greater than 0/);
+
+    test.done();
+  },
 };