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AWS ECS - L3 Construct for Autoscaling ECS/Fargate Service that Processes Items in a SQS Queue

To address issue #2396, the AWS ECS CDK construct library should provide a way for customers to create a queue processing service (an AWS ECS/Fargate service that processes items from an sqs queue). This would mean adding new ECS CDK constructs QueueProcessingEc2Service and QueueProcessingFargateService, that would take in the necessary properties required to create a task definition, an SQS queue as well as an ECS/Fargate service and enable autoscaling for the service based on cpu usage and the SQS queue's approximateNumberOfMessagesVisible metric.

General approach

The new ecs.QueueProcessingServiceBase, ecs.QueueProcessingEc2Service and ecs.QueueProcessingFargateService classes will create L3 constructs for:

  • QueueProcessingEc2Service
  • QueueProcessingFargateService

A QueueProcessingService will create a task definition with the specified container (on both EC2 and Fargate). An AWS SQS Queue will be created and autoscaling of the ECS Service will be dependent on both CPU as well as the SQS queue's ApproximateNumberOfMessagesVisible metric.

The QueueProcessingService constructs (for EC2 and Fargate) will use the following existing constructs:

  • Ec2TaskDefinition/FargateTaskDefinition - To create a Task Definition for the container to start
  • SQSQueue - The queue that the service is processing from
  • Ec2Service/FargateService - The Service running the container

Code changes

Given the above, we should make the following changes to support queue processing on ECS (for both EC2 and Fargate):

  1. Create QueueProcessingServiceBaseProps interface and QueueProcessingServiceBase construct
  2. Create QueueProcessingEc2ServiceProps interface and QueueProcessingEc2Service construct
  3. Create QueueProcessingFargateServiceProps interface and QueueProcessingFargateService construct

Part 1: Create QueueProcessingServiceBaseProps interface and QueueProcessingServiceBase construct

The QueueProcessingServiceBaseProps interface will contain common properties used to construct both the QueueProcessingEc2Service and the QueueProcessingFargateService:

/**
 * Properties to define a queue processing service
 */
export interface QueueProcessingServiceBaseProps {
  /**
   * Cluster where service will be deployed
   */
  readonly cluster: ICluster;

  /**
   * The image to start.
   */
  readonly image: ContainerImage;

  /**
   * The CMD value to pass to the container as a string array.
   *
   * @default none
   */
  readonly command?: string[];

  /**
   * Number of desired copies of running tasks
   *
   * @default 1
   */
  readonly desiredTaskCount?: number;

  /**
   * Flag to indicate whether to enable logging
   *
   * @default true
   */
  readonly enableLogging?: boolean;

  /**
   * The environment variables to pass to the container.
   *
   * @default 'QUEUE_NAME: queue.queueName'
   */
  readonly environment?: { [key: string]: string };

  /**
   * A queue for which to process items from.
   *
   * If specified and this is a FIFO queue, the queue name must end in the string '.fifo'.
   * @see https://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/API_CreateQueue.html
   *
   * @default 'SQSQueue with CloudFormation-generated name'
   */
  readonly queue?: IQueue;

  /**
   * Maximum capacity to scale to.
   *
   * @default (desiredTaskCount * 2)
   */
  readonly maxScalingCapacity?: number

  /**
   * The intervals for scaling based on the SQS queue's ApproximateNumberOfMessagesVisible metric.
   *
   * Maps a range of metric values to a particular scaling behavior.
   * https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-scaling-simple-step.html
   *
   * @default [{ upper: 0, change: -1 },{ lower: 100, change: +1 },{ lower: 500, change: +5 }]
   */
  readonly scalingSteps: autoScaling.ScalingInterval[];
}

Part 2: Create QueueProcessingEc2ServiceProps interface and QueueProcessingEc2Service construct

The QueueProcessingEc2ServiceProps interface will contain properties to construct the Ec2TaskDefinition, SQSQueue and Ec2Service:

/**
 * Properties to define an ECS service
 */
export interface QueueProcessingEc2ServiceProps {
  /**
   * The minimum number of CPU units to reserve for the container.
   *
   * @default - No minimum CPU units reserved.
   */
  readonly cpu?: number;

  /**
   * The hard limit (in MiB) of memory to present to the container.
   *
   * If your container attempts to exceed the allocated memory, the container
   * is terminated.
   *
   * At least one of memoryLimitMiB and memoryReservationMiB is required for non-Fargate services.
   *
   * @default - No memory limit.
   */
  readonly memoryLimitMiB?: number;

  /**
   * The soft limit (in MiB) of memory to reserve for the container.
   *
   * When system memory is under contention, Docker attempts to keep the
   * container memory within the limit. If the container requires more memory,
   * it can consume up to the value specified by the Memory property or all of
   * the available memory on the container instance—whichever comes first.
   *
   * At least one of memoryLimitMiB and memoryReservationMiB is required for non-Fargate services.
   *
   * @default - No memory reserved.
   */
  readonly memoryReservationMiB?: number;
}

An example use case:

// Create the vpc and cluster used by the queue processing service
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')
});
const queue = new sqs.Queue(stack, 'ProcessingQueue', {
  QueueName: 'EcsEventQueue'
});

// Create the queue processing service
new QueueProcessingEc2Service(stack, 'QueueProcessingEc2Service', {
  cluster,
  image: ecs.ContainerImage.fromRegistry('amazon/amazon-ecs-sample'),
  desiredTaskCount: 2,
  maxScalingCapacity: 5,
  memoryReservationMiB: 512,
  cpu: 256,
  queue
});

Part 3: Create QueueProcessingFargateServiceProps interface and QueueProcessingFargateService construct

The QueueProcessingFargateServiceProps interface will contain properties to construct the FargateTaskDefinition, SQSQueue and FargateService:

/**
 * Properties to define a Fargate service
 */
export interface QueueProcessingFargateServiceProps {
  /**
   * The number of cpu units used by the task.
   * Valid values, which determines your range of valid values for the memory parameter:
   * 256 (.25 vCPU) - Available memory values: 0.5GB, 1GB, 2GB
   * 512 (.5 vCPU) - Available memory values: 1GB, 2GB, 3GB, 4GB
   * 1024 (1 vCPU) - Available memory values: 2GB, 3GB, 4GB, 5GB, 6GB, 7GB, 8GB
   * 2048 (2 vCPU) - Available memory values: Between 4GB and 16GB in 1GB increments
   * 4096 (4 vCPU) - Available memory values: Between 8GB and 30GB in 1GB increments
   *
   * This default is set in the underlying FargateTaskDefinition construct.
   *
   * @default 256
   */
  readonly cpu?: string;

  /**
   * The amount (in MiB) of memory used by the task.
   *
   * This field is required and you must use one of the following values, which determines your range of valid values
   * for the cpu parameter:
   *
   * 0.5GB, 1GB, 2GB - Available cpu values: 256 (.25 vCPU)
   *
   * 1GB, 2GB, 3GB, 4GB - Available cpu values: 512 (.5 vCPU)
   *
   * 2GB, 3GB, 4GB, 5GB, 6GB, 7GB, 8GB - Available cpu values: 1024 (1 vCPU)
   *
   * Between 4GB and 16GB in 1GB increments - Available cpu values: 2048 (2 vCPU)
   *
   * Between 8GB and 30GB in 1GB increments - Available cpu values: 4096 (4 vCPU)
   *
   * This default is set in the underlying FargateTaskDefinition construct.
   *
   * @default 512
   */
  readonly memoryMiB?: string;
}

An example use case:

// Create the vpc and cluster used by the queue processing service
const vpc = new ec2.Vpc(stack, 'Vpc', { maxAzs: 2 });
const cluster = new ecs.Cluster(stack, 'FargateCluster', { vpc });
const queue = new sqs.Queue(stack, 'ProcessingQueue', {
  QueueName: 'FargateEventQueue'
});

// Create the queue processing service
new QueueProcessingFargateService(stack, 'QueueProcessingFargateService', {
  cluster,
  image: ecs.ContainerImage.fromRegistry('amazon/amazon-ecs-sample'),
  desiredTaskCount: 2,
  maxScalingCapacity: 5,
  queue
});