I had a heck of a time this week trying to figure out how to get Upstart to start an instance of Unicorn due to the fact that Ruby was being managed with RVM. I finally realized I had been going about it the wrong way, and that RVM provided the tool that I needed: wrapper scripts. I opted to use a single wrapper script for the version of Ruby I was running, and to let Unicorn decide what gemset to use based on the .rvmrc file in the project. Here’s the whole process:

Step 1: Make sure Unicorn is installed in the global gemset

rvm use ruby-1.9.2-p136@global
gem install unicorn

Step 2: Create a wrapper script for Unicorn

rvm wrapper ruby-1.9.2-p136 r192 unicorn

Step 3: Modify your Upstart configuration file’s “exec” line

exec /usr/local/rvm/bin/r192_unicorn -c /path/to/app/config/unicorn.rb

Step 4: Modify your config/unicorn.rb file

Use the following code at the top of your unicorn.rb file to tell Unicorn to set up the environment based on the .rvmrc file in the root of the project:

if ENV['MY_RUBY_HOME'] && ENV['MY_RUBY_HOME'].include?('rvm')
  begin
    rvm_path     = File.dirname(File.dirname(ENV['MY_RUBY_HOME']))
    rvm_lib_path = File.join(rvm_path, 'lib')
    $LOAD_PATH.unshift rvm_lib_path
    require 'rvm'
    RVM.use_from_path! File.dirname(File.dirname(__FILE__))
  rescue LoadError
    raise "The RVM Ruby library is not available."
  end
end

ENV['BUNDLE_GEMFILE'] = File.expand_path('../Gemfile', File.dirname(__FILE__))
require 'bundler/setup'

Step 5: Start your service

Now you should be able to start your Unicorn app via sudo service start appname.