RabbitCarrots

RabbitCarrots is a simple background task based on rake to handle the consumption of RabbitMQ message in Rails applications. It is an opinionated library that solves the consumption of messages among microservices, given the following conditions:

1. RabbitMQ is used as an event bus for communication.
2. Messages are routed using a single exchange, multiple routing keys.
3. One routing key or more can be bound to a single queue.
4. The app is a built with Ruby on Rails.

Considerations

The gem adds a rake task to the project using the Railtie framework of Rails. Therefore, the task should be run as a separate process that is independent from the application server.

Installation

Install the gem and add to the application's Gemfile by executing:

$ bundle add rabbit_carrots

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install rabbit_carrots

Usage

Add the following to config/initializers/rabbit_carrots.rb:

RabbitCarrots.configure do |c|
  c.rabbitmq_host = ENV.fetch('RABBITMQ__HOST', nil)
  c.rabbitmq_port = ENV.fetch('RABBITMQ__PORT', nil)
  c.rabbitmq_user = ENV.fetch('RABBITMQ__USER', nil)
  c.rabbitmq_password = ENV.fetch('RABBITMQ__PASSWORD', nil)
  c.rabbitmq_vhost = ENV.fetch('RABBITMQ__VHOST', nil)
  c.rabbitmq_exchange_name = ENV.fetch('RABBITMQ__EXCHANGE_NAME', nil)
  c.automatically_recover = true
  c.network_recovery_interval = 5
  c.recovery_attempts = 5
  c.orm = :activerecord || :mongoid
  c.routing_key_mappings =  [
    { routing_keys: ['RK1', 'RK2'], queue: 'QUEUE_NAME', handler: 'CLASS HANDLER IN STRING' },
    { routing_keys: ['RK1', 'RK2'], queue: 'QUEUE_NAME', handler: 'CLASS HANDLER IN STRING' }
  ]
end

Note that handler is a class that must implement a method named handle! that takes 4 parameters as follow:

class DummyEventHandler
   def self.handle!(channel, delivery_info, properties, payload)
      # Handle the received message from the queue 
   end
end

Inside the handle message, you can NACK the message without re-queuing by raising RabbitCarrots::EventHandlers::Errors::NackMessage exception.

To NACK and re-queue, raise RabbitCarrots::EventHandlers::Errors::NackAndRequeueMessage exception.

If no errors are thrown, the message will be acknowledged soon after the handle! method returns.

Note: Any other unrescued exception raised inside handle! the that is a subclass of StandardError will trigger a NACK and re-queue.

Running

For better scalability and improved performance, you can run rabbit_carrots in standalone mode by invoking the following command: bundle exec rake rabbit_carrots:eat.

Puma

For small and medium sized projects, you can delegate the management of the rabbit_carrots to the Puma web server. To achieve that, add the following line to your puma.rb

plugin :rabbit_carrots

This will make sure that Puma will manage rabbit carrots as a background service and will gracefully terminate if rabbit_carrots eventually loses connection after multiple automatic recovery.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ditkrg/rabbit_carrots. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the RabbitCarrots project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.