#Rails Background Workers

Tonight we will discuss background workers. We'll cover:

• What a background worker is
• Why they're awesome
• When to use them

Then we will install Redis (for Sidekiq) and add Sidekiq to an existing app, Gifster.

##Background Workers

Background workers are separate processes that can run along side a Rails server.

##Getting Started with Sidekiq

1. First we need to install Redis. We can do that via homebrew: $ brew install redis. Paste the followup instruction to keep Redis running locally.

2. We check Redis is running by pinging it with $ redis-cli ping.

3. Let's add Sidekiq to our Gemfile:

   # rest of Gemfile
   
   gem 'sidekiq'
   

   Then bundle install.

4. You can test Sidekiq is worker by starting it in a separate tab: bundle exec sidekiq. If it starts and then waits for jobs, we're good.

##Our First Worker

5. Now, we can write our first worker:

   class WelcomeEmailWorker
     include Sidekiq::Worker
   
     def perform(user_id)
       user = User.find(user_id)
       WelcomeMailer.welcome_email(user).deliver
     end
   end

6. How do we run a Sidekiq worker? Simple: WelcomeEmailWorker.perform_async(1). But the task won't actually be done until we start the Sidekiq process.

7. To start Sidekiq, open a new tab and run: bundle exec sidekiq. You should see the jump start and finish.

##Moving Image Processing Into Sidekiq

8. For image process, we need an additional gem to help: Carrierwave Backgrounder. This gem ties into Carrierwave to handle the actual image files so we can move them to the background. Add gem 'carrierwave_backgrounder' to your Gemfile and bundle!

9. After bundling, we run the installer script: $ rails g carrierwave_backgrounder:install. Then adjust the config file to use Sidekiq.

10. Now, we need to include this module in our Uploader:

    class ImageUploader < CarrierWave::Uploader::Base
      include ::CarrierWave::Backgrounder::Delay
    
      # rest of the file

11. We need to tell the GIF model to use the backgrounder:

    class Gif < ActiveRecord::Base
      mount_uploader :image, ImageUploader
      store_in_background :image
    
    # rest of the file

    And we need to add a column called image_tmp to our Gif to handle the temporary image.

12. We also need to create a sidekiq.yml file to create a queue for carrierwave.

    # config/sidekiq.yml
    
    :queues:
      - [default, 5]
      - [carrierwave, 3]
    

13. If all of that worked, our form now remotes handles image uploads! Restart your server and start sidekiq to see!

Awesome. Now our app easily moves jobs to a Sidekiq worker!