serverless-tasks-handel-extension

Serverless Tasks Handel Extension

This repository contains a Handel extension that provides serverless scheduled tasks using ECS Fargate.

Motivation

As of Jun. 2018, Fargate doesn't have built-in support for scheduled tasks. You can accomplish this with CloudWatch Events, Lambda, and Fargate working in concert.

The above setup works great, but it requires quite a bit of CloudFormation, particularly when wiring the permissions together properly.

This Handel extension aims to provide that functionality with only a line or two of configuration.

Usage

To use this extension, add it to the extensions section of your Handel file, and then add the scheduledtask service to your environment:

version: 1

name: schedtask-example

extensions: # This tells Handel to import this extension
  tasks: serverless-tasks-handel-extension # This is the NPM package name of this extension

environments:
  dev:
    task:
      type: tasks::scheduledtask # You must use the <extensionName>::<serviceType> syntax here
      schedule: rate(1 minute) # Required. See https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/ScheduledEvents.html for what to put here
      image_name: dsw88/handel-scheduled-task-example # Optional. The Docker image that should be executed as the task
      work_dir_path: '/mnt/share/workdir' # Optional. The directory where the task 8GB working directory should be mounted
      max_mb: 2048 # Optional. Default: 512. The amount of memory in MB to allocate to the task
      cpu_units: 1024 # Optional. Default: 256. The amount of CPU units to allocate to the task. 1 vCPU = 1024.
      environment_variables: # Optional. Any environment variables that should be passed to the task
        MY_ENV: myValue

That's all the configuration you need to do! Once you deploy this app using Handel, your task will execute on the schedule you've defined.

Image Names

The image_name parameter can take several forms:

If you want to pull a public image from somewhere like DockerHub, just reference the image name directly:

dsw88/handel-scheduled-task-example

If you want to reference an image in your AWS account’s EC2 Container Registry (ECR), reference it like this:

# The <account> piece will be replaced with your account's long ECR repository name
<account>/handel-scheduled-task-example

If you don’t specify an image_name, this extension will automatically choose an image name for you based on your Handel naming information. It will use the following image naming pattern:

<appName>-<serviceName>-<containerName>:<environmentName>

For example, if you don’t specify an image_name in the above example Handel file, the image this extension will look for is the following:

schedtask-example-task:dev

Working Directory

You are provided with a 4GB mounted volume in each task. This can be used as scratch space for your tasks.

You can use the optional work_dir_path parameter to configure where this volume should be mounted in your container.

If you don't specify the work_dir_path parameter, this volume will be mounted at the following default location:

/mnt/share/task-workdir

Be aware that this scratch space does not persist across tasks!