CSC/ECE 517 Spring 2016/Active Job

Introduction

Active Job is a framework that helps developers to write codes and run them on the background automatically under different scenarios. It’s an interface that adapts various queueing backends like Backburner, Delayed Job, Qu and so on. Jobs can vary from schedule newsletters, follow-up emails to database housekeeping. <ref name= "Active-Job-Basics">Rails Guides “Active Job Basics” </ref> Overall, Active Job is an interface which you can work with common queueing backends. The reason to have Active Job in place is to make sure Rails apps can have a job infrastructure. Other existing gems can build on this framework without the limitation of API difference between different job runners such as Delayed Job and Resque. With this feature choosing queueing backends can become an operational concern. Also, switching between those queueing backends without rewrite jobs become possible.<ref name= "Active-Job-Basics">Rails Guides “Active Job Basics” </ref>

Ruby On Rails versions support Active Job

Version history

Version	Date
4.2	2014/12/19
4.2.5	2015/11/13

Active Job adapters<ref name="Active-Job-Adapter">Active Job Adapter"Active Job Adapter" </ref>

List of queueing backends Active Job support:

• Backburner[1]
• Delayed Job[2]
• Qu[3]
• Que[4]
• queue_classic[5]
• Resque 1.x[6]
• Sidekiq[7]
• Sneakers[8]
• Sucker Punch[9]
• Active Job Async Job
• Active Job Inline[10]

How to use <ref>http://guides.rubyonrails.org/active_job_basics.html</ref>

This chapter is an introduction on how to create a job and and how to add the job into a queue. <ref name= "Active-Job-Basics">Rails Guides “Active Job Basics” 2014</ref>

Download

With RubyGems[11] you can install Active Job:

$ gem install activejob

Souce code of Active Job available on GitHub[12], as part of Rails.<ref> GitHub “Active Job -- Make work happen later” 2015 </ref>

Create a Job

In Active Job, a process inserted in a queue and waiting to carry out is called “Job”. It’s possible to generate a Job using the Generator provided by Rails. You can create a Job in app/jobs. By doing the following, we created a Job called “update_wiki”.

$ bin/rails generate job update_wiki
  invoke  test_unit
  create  test/jobs/update_wiki_job_test.rb
  create  app/jobs/update_wiki_job.rb

Active Job provides the ability to run your Job on a specific queue by creating a job:

$ bin/rails generate job update_wiki --queue urgent

Files inside of app/jobs can be created manually, instead of using a generator. In Rails 4.2 an ActiveJob class inherits from ActiveJob::Base. In Rails 5.0, it has changed to now inherit from ApplicationJob. When upgrading from Rails 4.2 to Rails 5.0, an application_job.rb file is needed to be created in app/jobs/ and add the following content:<ref> Rails Guides “A Guide for Upgrading Ruby on Rails” 2015 </ref>

class ApplicationJob < ActiveJob::Base
end

In Rails 4.2 a Job class defined a perform method and set a “queue_as” value:

class UpdateWikiJob < ActiveJob::Base
  queue_as :default
 
  def perform(*wiki)
   # Do something later
  wiki.update_contents
  end
end

There is a perform method to be called when the Job was first enqueued.

Adding a Job to the queue

Enqueue the Job so it can be processed as soon as the queuing system is free:

UpdateWikiJob.perform_later wiki

Or add a Job be performed tomorrow at noon:

UpdateWikiJob.set(wait_until: Date.tomorrow.noon).perform_later(wiki)

Most of the queueing backends ( Sidekiq , Delayed Job, etc. ) allow you to set a delay time.

UpdateWikiJob.set(wait: 1.week).perform_later(wiki)

Execution of Job

Active Job provides adapters for multiple queueing backends (Sidekiq, Resque, Delayed Job and others).<ref name= "Active-Job-Basics">Rails Guides “Active Job Basics” 2014</ref> Without setting any adapter, the job would be performed immediately.
Queueing backend can be set at: /config/application.rb, this example uses the Sidekiq.

module YourApp
  class Application < Rails::Application
    # Be sure to have the adapter's gem in your Gemfile and follow
    # the adapter's specific installation and deployment instructions.
    config.active_job.queue_adapter = :sidekiq
  end
end

Play with Queues

Active Job allows to schedule the job to be processed on a specific queue, this became helpful as common adapters support multiple queues.

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

Queue name can be prefixed for all jobs using config.active_job.queue_name_prefixin application.rb:

# config/application.rb
module YourApp
  class Application < Rails::Application
    config.active_job.queue_name_prefix = Rails.env
  end
end
 
# app/jobs/update_wiki_job.rb
class UpdateWikiJob < ActiveJob::Base
  queue_as :low_priority
  #....
end
 
# Now your job will run on queue production_low_priority on your
# production environment and on staging_low_priority on your staging
# environment

Control a job to run on a queue by passing a :queue option to #set :

MyJob.set(queue: :another_queue).perform_later(record)

All the code snippets are referred from the source<ref name= "Active-Job-Basics">Rails Guides “Active Job Basics” 2014</ref>

Examples

In this section, a example is provided to demonstrate how to use ActiveJob in practice.

Background Mail Sender

Send emails asynchronously with Action Mailer which Active Job is already integrated in.<ref name= "Action-Mailer-Basics">Rails Guides “Action Mailer Basics” 2014</ref> Here in this example, we try to use Active Job with Action Mailer.

1. Getting started with Rails<ref name= "Welcome_to_Rails">GitHub “Welcome to Rails” 2015</ref>

# Install Rails if you haven’t done it yet:
$ gem install rails

# Create a new Rails application, “myapp_activejob”
# is the name of the application:
$ rails new myapp_activejob

# Change your directory to myapp_activejob
$ cd myapp_activejob

Edit the Gemfile in the folder, add following into it:

gem 'responders'

Run “ $ bundle update “ and make sure “$ rails server” works.

2. Resque setup<ref name= "Download_Redis">Redis “Download Redis” 2016</ref>

This example uses Resque as the enqueuing backend. It'll need Redis before running Resque. Redis can be installed using Homebrew:

$ brew install redis

Or download, extract and compile Redis using:<ref name= "Download_Redis">Redis “Download Redis” 2016</ref>

$ wget http://download.redis.io/releases/redis-3.0.7.tar.gz
$ tar xzf redis-3.0.7.tar.gz
$ cd redis-3.0.7
$ make

Redis does not officially support Microsoft Windows platform, but it can be found Redis on Windows by Microsoft Open Tech group.
Next get Resque be installed. To use resque with Active Job, we also need resque-scheduler. Add the following into Gemfile, and run “$ bundle install”.

gem 'resque'
gem 'resque-scheduler'

After the installation, create a Resque configuration file resque.rb in config/initializers/

#config/initializers/resque.rb

Resque.redis = Redis.new(host: 'localhost', post: 6379)
Resque.after_fork = Proc.new { ActiveRecord::Base.establish_connection }

As the Resque tasks and Resque Scheduler rake tasks are needed in this example, we need to create a resque.rake file in lib/tasks/:

#lib/tasks/resque.rake

require 'resque/tasks'
require 'resque/scheduler/tasks'

namespace :resque do
  task setup: :environment do
    ENV['TERM_CHILD'] ||= '1'
    ENV['QUEUE'] ||= '*'
    require 'resque'
    require 'resque-scheduler'
  end
end

3. Creating a Mailer<ref name= "Action-Mailer-Basics">Rails Guides “Action Mailer Basics” 2014</ref>

By doing the things above, we already have our Rails project and the Resque for queuing get set. Next we will create a Mailer.

$ bin/rails generate mailer user_mailer

Create a method and a view for sending the email.
In app/mailer/user_mailer.rb:

#app/mailers/user_mailer.rb

class UserMailer < ActionMailer::Base
  default from: 'from@example.com'

  def test_email(email)
    mail(
      to: email,
      subject: 'We are testing Active Job!'
    )
  end
end

In app/views/user_mailer/test_email.text

#app/views/user_mailer/test_email.text

Hey, we are testing Active Job!

4. Active Job<ref name= "Active-Job-Basics">Rails Guides “Active Job Basics” 2014</ref>

Create a configuration file active_job.rb in config/initializers/ , to set Resque as queue_adapter.

#config/initializers/active_job.rb

ActiveJob::Base.queue_adapter = :resque

Create a Job with generator.

$ bin/rails generate job test_email

In the generated file app/jobs/test_email_job.rb, define the perform method and set it’s queue_as.

#app/jobs/test_email_job.rb

class TestEmailJob < ActiveJob::Base
  queue_as :email

  def perform(email)
    UserMailer.test_email(email).deliver_now
  end
end

Now a UserController is in place to put the job into the queue for later execution. Set the email to be sent one minute later for testing.

$ bin/rails generate job test_email

#app/controllers/users_controller.rb

class UsersController < ApplicationController
  def new
    @user = User.new
  end

  def create
    @user = User.create(user_params)
    TestEmailJob.new(@user.email).deliver_later!(wait: 1.minute)
    # redirect somewhere
  end
end

Routes and views need to be set in order to make it work.

#config/routes.rb

Rails.application.routes.draw do
  resources :users, only: [:new, :create]
end

#app/views/users/new.html.erb

<%= form_for @user do |f| %>
  <%= f.email_field :email %>
  <%= f.submit %>
<% end %>

5. Try execution

Before trying the Mailer, MailCatcher[13] is needed for the test. Add following into Gemfile and “$ bundle install”

gem 'mailcatcher'

To set the environment, one need to add the following into config/environments/development.rb.

#config/environments/development.rb

Rails.application.configure do
  ...
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = { address: "localhost", port: 1025 }
end

Run it!

# Start mailcatcher
$ mailcatcher

# Start redis-server
$ redis-server

# Start resque:work
$ bundle exec rake resque:work

# Start resque:scheduler
$ rake environment resque:scheduler

# Finally start rails server
$ rails server

Open the browser and visit localhost:3000/users/new. Then sign up as a new user. One minute later Resque scheduler has following output:

resque-scheduler: [INFO] 2016-02-05T22:53:15+09:00: Processing Delayed Items

And in MailCatcher:

==> SMTP: Received message from '<from@example.com>' (315 bytes)

External links

• Ruby on Rails official website – rubyonrails.org
• Railscasts.com – (defunct) Short Screencasts that focus on Ruby on Rails technique
• Rubycasts.io – Weekly 15 minute screencasts on the whole Ruby/Rails development stack
• The Rails Tutorial – The Ruby on Rails Tutorial book and screencast series teach you how to develop and deploy Ruby on Rails apps
• Rails source code

References

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