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Active Job Basics

This guide provides you with all you need to get started in creating, enqueueing and executing background jobs.

After reading this guide, you will know:

  • How to create jobs.
  • How to enqueue jobs.
  • How to run jobs in the background.
  • How to send emails from your application async.

Introduction

Active Job is a framework for declaring jobs and making them run on a variety of queueing backends. These jobs can be everything from regularly scheduled clean-ups, billing charges, or mailings. Anything that can be chopped up into small units of work and run in parallel, really.

The Purpose of the Active Job

The main point is to ensure that all Rails apps will have a job infrastructure in place, even if it's in the form of an "immediate runner". We can then have framework features and other gems build on top of that, without having to worry about API differences between various job runners such as Delayed Job and Resque. Picking your queuing backend becomes more of an operational concern, then. And you'll be able to switch between them without having to rewrite your jobs.

Creating a Job

This section will provide a step-by-step guide to creating a job and enqueue it.

Create the Job

Active Job provides a Rails generator to create jobs. The following will create a job in app/jobs:

$ bin/rails generate job guests_cleanup
create  app/jobs/guests_cleanup_job.rb

You can also create a job that will run on a specific queue:

$ bin/rails generate job guests_cleanup --queue urgent
create  app/jobs/guests_cleanup_job.rb

As you can see, you can generate jobs just like you use other generators with Rails.

If you don't want to use a generator, you could create your own file inside of app/jobs, just make sure that it inherits from ActiveJob::Base.

Here's how a job looks like:

class GuestsCleanupJob < ActiveJob::Base
  queue_as :default

  def perform
    # Do something later
  end
end

Enqueue the Job

Enqueue a job like so:

MyJob.enqueue record  # Enqueue a job to be performed as soon the queueing system is free.
MyJob.enqueue_at Date.tomorrow.noon, record  # Enqueue a job to be performed tomorrow at noon.
MyJob.enqueue_in 1.week, record # Enqueue a job to be performed 1 week from now.

That's it!

Job Execution

If not adapter is set, the job is immediately executed.

Backends

Active Job has adapters for the following queueing backends:

Backends Features

Async Queues Delayed Priorities Timeout Retries
Backburner Yes Yes Yes Yes Job Global
Delayed Job Yes Yes Yes Job Global Global
Que Yes Yes Yes Job No Job
Queue Classic Yes Yes Gem No No No
Resque Yes Yes Gem Queue Global ?
Sidekiq Yes Yes Yes Queue No Job
Sneakers Yes Yes No Queue Queue No
Sucker Punch Yes Yes Yes No No No
Active Job Yes Yes WIP No No No
Active Job Inline No Yes N/A N/A N/A N/A

Change Backends

You can easy change your adapter:

# be sure to have the adapter gem in your Gemfile and follow the adapter specific
# installation and deployment instructions
YourApp::Application.config.active_job.queue_adapter = :sidekiq

Queues

Most of the adapters supports multiple queues. With Active Job you can schedule the job to run on a specific queue:

class GuestsCleanupJob < ActiveJob::Base
  queue_as :low_priority
  #....
end

NOTE: Make sure your queueing backend "listens" on your queue name. For some backends you need to specify the queues to listen to.

Callbacks

Active Job provides hooks during the lifecycle of a job. Callbacks allows you to trigger logic during the lifecycle of a job.

Available callbacks

  • before_enqueue
  • around_enqueue
  • after_enqueue
  • before_perform
  • around_perform
  • after_perform

Usage

class GuestsCleanupJob < ActiveJob::Base
  queue_as :default

  before_enqueue do |job|
    # do somthing with the job instance
  end

  around_perform do |job, block|
    # do something before perform
    block.call
    # do something after perform
  end

  def perform
    # Do something later
  end
end

ActionMailer

One of the most common jobs in a modern web application is sending emails outside of the request-response cycle, so the user doesn't have to wait on it. Active Job is integrated with Action Mailer so you can easily send emails async:

# Instead of the classic
UserMailer.welcome(@user).deliver

# use #deliver later to send the email async
UserMailer.welcome(@user).deliver_later

GlobalID

Active Job supports GlobalID for parameters. This makes it possible to pass live Active Record objects to your job instead of class/id pairs, which you then have to manually deserialize. Before, jobs would look like this:

class TrashableCleanupJob
  def perform(trashable_class, trashable_id, depth)
    trashable = trashable_class.constantize.find(trashable_id)
    trashable.cleanup(depth)
  end
end

Now you can simply do:

class TrashableCleanupJob
  def perform(trashable, depth)
    trashable.cleanup(depth)
  end
end

This works with any class that mixes in ActiveModel::GlobalIdentification, which by default has been mixed into Active Model classes.

Exceptions

Active Job provides a way to catch exceptions raised during the execution of the job:

class GuestsCleanupJob < ActiveJob::Base
  queue_as :default

  rescue_from(ActiveRecord:NotFound) do |exception|
   # do something with the exception
  end

  def perform
    # Do something later
  end
end