Intermediary

This gems aims to unify asynchronous communication between different apps in a SOA.

It is built on top of the awesome bunny gem, which provides an interface to RabbitMQ.

The emitter (the app that publishes updates) in this gem does not know who consumes those updates. To this end a topic exchange is being used. To make subscribing to updates as straightforward as possible the exchange key mimics restful routes. Updates to resources are published in an exchange key that reflects the resource's href (down to the host).

Installation

Add this line to your application's Gemfile:

gem 'intermediary'

And then execute:

$ bundle

Or install it yourself as:

$ gem install intermediary

Usage

As explained above, gem provides two elements to exchange updates between apps:

• The emitter
• The listener

The Emitter

To use the emitter one simply inherits from Intermediary::Emitters::Base as follows:

class MyEmitter < Intermediary::Emitters::Base
  def href
    # Some fance href generation...
  end
end

Per default the initializer takes one argument (the object). As everything else it can be customized by overwriting it.

The href method always has to be supplied to indicate how to construct the routing key.

Per default the payload emitted is the the object's .attributes and the event.

The Listener

The receiver is merely a user-defined class that implements the following method: self.act. Which takes three arguments: payload, routing_key and properties. The payload will be a hash.

Furthermore the class has to define @queue_name and @routing_key.

Example:

class MyListener
  @queue_name  = "my-awesome-queue"
  @routing_key = "app_example_com.model.#"

  def self.act(payload, routing_key, properties)
    puts payload.inspect
  end
end

Please note that multiple receivers with the same queue name will share items!

To register a listener, please call the following (e.g. in an initializer):

Intermediary::Listeners.register MyListener

Additionally one can define a self.on_error method with takes one argument: The error itself. It will get called when processing a job failed. Feel free to pass it to your favorite error tracker.

Pro tip

If you want to share the same on_error handler amongst multiple listeners, how about using a module, eh?

Contributing

1. Fork it ( http://github.com//intermediary/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request