How to use a bundler group to define a reduced-memory consumption environment for your workers

Gemfile

# these gems won't be loaded by our Rakefile with WORKER_ENVIRONMENT enabled
gem 'rails', '3.0.3'
gem 'haml', '3.1.0.alpha.147'
# ...

# load these both for the app and the workers
group :default, :worker do
  gem 'mongo', '1.1.5'
  gem 'bson', '1.1.5'
  gem 'bson_ext', '1.1.5'
  gem 'mongomatic', '0.7.3'
  gem 'i18n', '0.5.0'
  gem 'configatron', '2.6.4'
  gem 'resque', '1.10.0'
  # careful, the next version apparently requires redis > 1.3
  gem 'resque-scheduler', '1.9.6'
  gem 'hoptoad_notifier', '2.4.2'
  # ...
end

Rakefile

unless ENV['WORKER_ENVIRONMENT'] == '1'
  require File.expand_path('../config/application', __FILE__)
  MyApp::Application.load_tasks
else
  require 'rubygems'
  require 'bundler'

  ENV['BUNDLE_GEMFILE'] = File.expand_path('Gemfile', File.dirname(__FILE__))
  Bundler.require(:worker)
end

require 'rake'
require 'resque/failure/multiple'
require 'resque/failure/redis'
require 'resque/failure/hoptoad'
require 'resque/tasks'
require 'resque_scheduler/tasks'

# note - resque:setup doesn't depend on :environment in this mode 
task "resque:setup" do
  # ...

  Resque::Failure::Hoptoad.configure do |config|
    config.api_key = 'xxxx'
  end
  
  # do this at the end to enable the multiple backend (last wins)
  Resque::Failure::Multiple.configure do |config|
    # keep Redis first
    config.classes = [Resque::Failure::Redis, Resque::Failure::Hoptoad]
  end
end