simple_publisher

Defines a simple pub/sub layer for interaction with the Starling message queue.

The Idea

More often than not you don't need a full fledged message queue like ActiveMQ or RabbitMQ with a full size message format. For simple asynchronous distribution tasks a very light weight persistent message queue like starling will be fine. Nevertheless you want a more sophisticated interface to interact with than a memcache interface. Simple Publisher tries to achieve exactly this: While using Starling as the queuing system in the background we provide a messaging terminology well know and understood. The terminology is strongly inspired by JMS which is kind a defacto standard for messaging on the API-level.

Example

The Simple Publisher gem only helps you on the publisher site of message based connection (as the name already suggests). For the other side, the subscriber you need to roll your own solution. But fortunately there are aleady a lot of options you could use. I would strongly recommend to have a look at the Workling plugin. Originally designed to realize easy background process integration into any Rails app, we could simply facilitate it to receive messages published by a different app. The following examples shows what you have to do on both the publisher and subscriber site.

First the publisher:

# Let's assume we build a distributed mailing service which will read abstract
# email-instances from a queue and deliver them asynchronously

# First: Define your Connection and Topic instances ...
topic      = SimplePublisher::Topic.new(:name => "mail_service_subscribers__deliver_mail") # As you will see, this maps to Worklings naming scheme
connection = SimplePublisher::StarlingConnection.new(:host => "127.0.0.1", :port => "22122") # this Starlings default port

# ... and now get a Publisher instance
publisher = SimplePublisher::Publisher.new(
  :topic      => topic,
  :connection => connection
)

# Now lets create our email object we want to deliver asynchronously
email = Email.new # this could be any kind of object, usually a simple type.
                  # If you want to send complex objects over a message queue,
                  # make sure the other side nows about those objects.
publisher.publish(email) # ... and publish it to starling

And here comes the subscriber, which is just another Rails-App:

# Inside our receiving Rails-App with the Workling plugin enabled we create a
# Workling class
class MailServiceSubscriber < Workling::Base

  def deliver_mail(email)
    begin
      Notifier.send("deliver_#{email[:name_of_mail]}", email)
      # Here we just call anything that will actually send the email out. The
      # email object is the same we published on the other side.
    rescue Exception => e
      # it is usually a good idea to log any errors ...
      Rails.logger.error "An Error occured: #{e.message} --- BACKTRACE:\n\t#{e.backtrace.join("\n\t")}"
    end
  end

end

Due to the fact, that Workling will listen on a topic that is dynamically created out of the Worklings class name and the single method inside it, we end up with a topic name like mail_service_subscribers__deliver_mail which refers to the Workling class MailServiceSubscriber and the method deliver_mail. You cannot configure the name of the topic using Workling but it is not a major drawback. You just have to now the convention.

Of course you have to start both the Starling system process and the Workling-Client instances. They are located in the scripts folder of your Rails-App.

Note on Patches/Pull Requests

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don't break it in a future version unintentionally.
• Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
• Send me a pull request. Bonus points for topic branches.

Copyright

Copyright (c) 2010 Dirk Breuer. See LICENSE for details.