This tutorial shows how to use distributed ruby to connect a rails application with another ruby service not running inside Rails.

Distributed Ruby (DRb)

I won’t waste time here explaining how to use DRb. Just a short example from Rubycentral with a very simple server:

require 'drb'

class TestServer
  def doit
    "Hello, Distributed World"
  end
end

aServerObject = TestServer.new
DRb.start_service('druby://localhost:9000', aServerObject)
DRb.thread.join # Don't exit just yet!

and an even simpler client:

require 'drb'
DRb.start_service
obj = DRbObject.new(nil, 'druby://localhost:9000')
# Now use obj
puts obj.doit

Active Record

As you want to connect the DRb Server to Rails, you probably want to use your model classes, too. Just include them (I’m still looking for a simple way to automagically include all models) and configure ActiveRecord:

require 'drb'
require 'rubygems'
require_gem 'activerecord'

require 'app/models/user.rb'

class Server
  def dump
    puts User.find(:first).inspect
  end
end

ActiveRecord::Base.establish_connection(
    :adapter  => "mysql",
    :username => "xxxx",
    :host     => "localhost",
    :password => "xxxx",
    :database => "xxxx"
)

DRb.start_service("druby://localhost:9000", Server.new)
puts DRb.uri
DRb.thread.join

Don’t repeat yourself!

Repeating the database configuration as I did in the above example is soooo against The Ruby Way. A better way is to parse config/database.yml and use the result to configure ActiveRecord. This has the added benefit of being able to use different database setups:

require 'drb'
require 'rubygems'
require 'yaml'
require_gem 'activerecord'

require 'app/models/user.rb'

class Server
  def dump
    puts User.find(:first).inspect
  end
end

abort "usage: #{__FILE__} environment" unless ARGV[0]
database_yaml = YAML.load_file("config/database.yml")
abort "environment '#{ARGV[0]}' not found" unless database_config = database_yaml[ARGV[0]]

ActiveRecord::Base.establish_connection(database_config)

DRb.start_service("druby://localhost:9000", Server.new)
puts DRb.uri
DRb.thread.join

From Rails?

Just use the simple client from above inside your model or controller without special changes for Rails. Yes, it’s that simple. Enjoy!

require 'drb'
...
class DrbController < ApplicationController

  def get_user_via_drb
    DRb.start_service
    obj = DRbObject.new(nil, 'druby://localhost:9000')
    @user = obj.dump
  end 

Here is a short thread about problems with DRb.

DRb over unix sockets

Brian has a nice writeup how to use DRb over unix sockets – it’s extremly easy, just change the URI et voila…

[tags]ruby, rails, drb[/tags]