Background processing using Resque

Today I added to my Webchatter app Resque gem. Resque is a very convenient tool for background processing. It comes with nice UI which allows browsing completed tasks or review those that failed. Tasks are stored in Redis so everything is working blazing fast.

If you want to add Resque to your existing app first you need to add two gems into your Gemfile:

gem 'resque'
gem 'resque-web', require: 'resque_web'

The second gem is not required, but in my opinion, it is really helpful for debugging purposes. When something is wrong with an asynchronous task you can simply check recently executed jobs from your browser and investigate why task failed. Then run bundle install and prepare your first Ruby class that will be executed asynchronusly (in the background):

# app/workers/send_email_notification_worker.rb
class SendEmailNotificationWorker
  @queue = :emailing

  def self.perform(user_id)
    user = User.find(user_id)
    NewCustomerNotification.call(user_id)
  end
end

As you can see there is nothing special in that class except @queue instance variable and self.perform method. Those two things are required by Resque. @queue defines the name of the queue on which task will be executed and perform method is fired by Resque once the task is processed.

Resque is using Redis for storing tasks data, so before we proceed to tests we need to make sure that Redis is up and running:

$ redis-server

Now let's add a route to our app so we can gain access to Resque web UI:

# config/routes.rb
mount ResqueWeb::Engine => "/resque_web"

Resque is working as a standalone system process, so before tests we need to start it:

$ cd app
$ bundle exec rake environment resque:work QUEUE=*

Through rails console we can run our ruby class asynchronously in the following way:

Resque.enqueue(SendEmailNotificationWorker, 666)

Above command will invoke perform method with 666 param of SendEmailNotificationWorker class asynchronously. I do not have User with id 666, so the task should not be executed. Let's check it out on Resque UI (http://localhost:3000/resque_web):