If you need to send transactional emails from your Rails application, you should always send them asynchronously using a background job. If you send transactional emails synchronously, the user will see a loading page for the time rails connect to SMTP server and delivers your email which is about 2-3 seconds. This will result in a very bad user experience and it’s advisable to send emails using a background job.

Sidekiq advertises it self as simple, efficient background processing engine for Ruby. Sidekiq has dependency on Redis version 2.4 or greater. Hence to setup Sidekiq on OpenShift, we have to setup Redis first. So let’s get started.

Setting up Redis

Redis cartridge for Openshift is available here. To add this cartridge to existing Openshift application, issue following command:

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rhc add-cartridge http://cartreflect-claytondev.rhcloud.com/reflect?github=smarterclayton/openshift-redis-cart

If this command fails, inspect the log files generated at $OPENSHIFT_REDIS_DIR/logs/redis.log.

Setting up Sidekiq

The Sidekiq community cartridge hasn’t been updated in a while and it doesn’t work with current OpenShift. Hence I forked the repository and fixed the issues. I also bumped the Sidekiq version to 3.3.1 which was latest at that time. You can see the code changes here.

To add Sidekiq cartridge to application, issue following command:

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rhc add-cartridge http://cartreflect-claytondev.rhcloud.com/github/pranavpr/openshift-origin-cartridge-sidekiq --app myapp

Once the installation completes, you can access the monitoring interface at https://YOUR_APP-NAMESPACE.rhcloud.com/sidekiq. Sidekiq will print the full URL with authentication after successful install.

Updating Gemfile

Add following line to your Gemfile to add Sidekiq to your Rails application:

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gem 'sidekiq'

Then do a bundle install to finish installation of sidekiq gem.

Send asynchronous emails using Sidekiq

Delayed extensions of Sidekiq allows sending emails asynchronously with Action Mailer out of the box. It provides three methods viz. delay, delay_for(interval) and delay_until(time), to send email asynchronously.

Use delay to deliver emails asynchronously, delay_for(interval) or delay_until(time) to deliver the email at some point in the future.

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UserMailer.delay.welcome_email(@user.id)
UserMailer.delay_for(5.days).find_more_friends_email(@user.id)
UserMailer.delay_until(5.days.from_now).find_more_friends_email(@user.id)

Devise emails

devise-async gem provides the ability to send Devise emails using Sidekiq. Add following line to the Gemfile:

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gem 'devise-async'

And then execute bundle install to finish installation of devise-async gem.

Now add :async to the devise call in your model:

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class User < ActiveRecord::Base
  devise :database_authenticatable, :async, :confirmable # etc ...
end

Finally set your queuing backend to Sidekiq by creating config/initializers/devise_async.rb:

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Devise::Async.backend = :sidekiq

Epilogue

I issued a pull request to merge my changes to community cartridge and it got accepted. So you can also use the community cartridge to add Sidekiq to your OpenShift application.