Chasqui

Chasqui adds persistent publish-subscribe (pub-sub) messaging capabilities to Sidekiq and Resque workers.

Installation

Add this line to your application's Gemfile

gem 'chasqui'

then execute

$ bundle

or install it yourself as

$ gem install chasqui

Dependencies

Chasqui uses Redis to store events and manage subscriptions. You can install Redis with your favorite package manager, such as homebrew, yum, or apt, or if you prefer, you can run vagrant up to run Redis in a virtual machine. If you already have Resque or Sidekiq working, then you already have everything you need to get started with Chasqui.

Quick Start

Start the broker

chasqui -r redis://localhost:6379/0

The broker is a ruby daemon that listens for events (messages) published to channels (topics) and forwards those events to registered subscribers. In order to work, your broker must use the same Redis database as your Sidekiq/Resque workers. For a list of available broker options, see chasqui --help.

Publish events

Chasqui.publish 'order.purchased', user, order

Publish an event to the order.purchased channel and include information about the user and order that triggered the event. Any arguments after the channel name must be JSON-serializable.

Define workers to handle events

With Sidekiq

class OrderPublishWorker
  include Sidekiq::Worker
  sidekiq_options queue: 'pubsub' # you can use any options sidekiq supports

  def perform(event, user, order_details)
    # custom logic to handle the event
  end
end

With Resque

class OrderPublishWorker
  @queue = 'pubsub' # choice of queue name is up to you

  def self.perform(event, user, order_details)
    # custom logic to handle the event
  end
end

The OrderPublishWorker is a normal Sidekiq (or Resque) worker. The first argument to the perform method is a Chasqui::Event object, and the remaining arguments are the same arguments you passed to Chasqui.publish.

Subscribe to events

Chasqui.subscribe do
  on 'order.purchased', PurchasedOrderWorker
  # ...more subscriptions
end

The above code tells Chasqui to place events published to the order.purchased channel on PurchaseOrderWorker's queue.

You can also use a callable object instead of a worker class to handle events.

Chasqui.subscribe queue: 'app_id:pubsub' do
  on 'order.purchased', ->(event, user, order) {
    logger.info event.to_json
  }
end

Running Subscribers

With Sidekiq

bundle exec sidekiq -q app_id:pubsub

With Resque

QUEUES=app_id:pubsub bundle exec rake resque:work

Subscribers are normal Sidekiq or Resque workers, and can take advantage of all available features and plugins. Please refer to the documentation for those libraries for detailed instructions.

• Sidekiq documentation
• Resque documentation

Configuration

Chasqui.configure do |c|
  c.redis = 'redis://my-redis.example.com:6379'
  ...
end

For a full list of configuration options, see the Chasqui::Config documentation.

Unsubscribing

Chasqui.unsubscribe 'order.purchased', 'app_id:pubsub'

If you no longer wish to handle events for a channel, you should unsubscribe the worker so that the Chasqui broker stops placing jobs on that worker's queue.

Why Chasqui?

• Persistent - events don't get lost when the broker restarts or your workers are not running.
• Integrates with the proven Sidekiq and Resque background worker libraries.
• Reduces service coupling - publishers have no knowledge of subscribers and subscribers have no knowledge of publishers.

Limitations

Chasqui requires that the publisher, broker, and all subscribers must connect to the same Redis database. If your applications use separate Redis databases, they will not be able to communicate with each other using Chasqui.

Contributing

• For feature requests, please open an issue to discuss the proposed feature.
• For bug fixes, you are welcome to create a pull request without first opening an issue.
• Except for documentation changes, tests are required with all pull requests.
• Please be polite and respectful when discussing the project with maintainers and your fellow contributors.

Code of Conduct

If you are unsure whether or not your communication is appropriate for Chasqui please consult the Chasqui Code of Conduct. If you suspect harassment or abuse, please report it to the email address listed in the Code of Conduct.