DCell

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"Objects can message objects transparently that live on other machines over the network, and you don't have to worry about the networking gunk, and you don't have to worry about finding them, and you don't have to worry about anything. It's just as if you messaged an object that's right next door." --Steve Jobs describing the NeXT Portable Distributed Object system

DCell is a simple and easy way to build distributed applications in Ruby. Somewhat similar to DRb, DCell lets you easily expose Ruby objects as network services, and call them remotely just like you would any other Ruby object. However, unlike DRb all objects in the system are concurrent. You can create and register several available services on a given node, obtain handles to them, and easily pass these handles around the network just like any other objects.

DCell is a distributed extension to Celluloid, which provides concurrent objects for Ruby with many of the features of Erlang, such as the ability to supervise objects and restart them when they crash, and also link to other objects and receive event notifications of when they crash. This makes it easier to build robust, fault-tolerant distributed systems.

DCell uses the 0MQ messaging protocol which provides a robust, fault-tolerant brokerless transport for asynchronous messages sent between nodes. DCell is built on top of the Celluloid::ZMQ library, which provides a Celluloid-oriented wrapper around the underlying ffi-rzmq library.

Please see the DCell Wiki for more detailed documentation and usage notes.

Like DCell? Join the Celluloid Google Group

Is it any good?

Yes.

Is It "Production Ready™"?

Not entirely, but eager early adopters are welcome!

Installation

Add this line to your application's Gemfile:

gem 'dcell'

And then execute:

$ bundle

Or install it yourself as:

$ gem install dcell

Inside of your Ruby program do:

require 'dcell'

...to pull it in as a dependency.

Example

Copy and paste this into itchy.rb (or run bundle exec examples/itchy.rb):

require 'dcell'

DCell.start :id => "itchy", :addr => "tcp://127.0.0.1:9001"

class Itchy
  include Celluloid

  def initialize
    puts "Ready for mayhem!"
    @n = 0
  end

  def fight
    @n = (@n % 6) + 1
    if @n <= 3
      puts "Bite!"
    else
      puts "Fight!"
    end
  end
end

Itchy.supervise_as :itchy
sleep

You can now launch itchy with:

ruby itchy.rb

Now copy and paste the following into scratchy.rb (also in examples)

require 'dcell'

DCell.start :id => "scratchy", :addr => "tcp://127.0.0.1:9002"
itchy_node = DCell::Node["itchy"]

puts "Fighting itchy! (check itchy's output)"

6.times do
  itchy_node[:itchy].fight
  sleep 1
end

Now run scratchy side-by-side with itchy. You should see this on itchy:

$ bundle exec examples/itchy.rb
Ready for mayhem!
I, [2012-12-25T22:52:45.362355 #74272]  INFO -- : Connected to scratchy
Bite!
Bite!
Bite!
Fight!
Fight!
Fight!

This is a basic example how individual DCell::Nodes have registered Celluloid actors which can be accessed remotely by other DCell::Nodes.

Supported Platforms

DCell works on Ruby 1.9.3, JRuby 1.6, and Rubinius 2.0.

DCell requires Ruby 1.9 mode on all interpreters. This works out of the box on MRI/YARV, and requires the following flags elsewhere:

  • JRuby: --1.9 command line option, or JRUBY_OPTS=--1.9 environment variable
  • rbx: -X19 command line option

Contributing to DCell

  • Fork this repository on github
  • Make your changes and send me a pull request
  • If I like them I'll merge them
  • If I've accepted a patch, feel free to ask for commit access

Copyright

Copyright (c) 2012 Tony Arcieri. Distributed under the MIT License. See LICENSE.txt for further details.