Unicorn config file used by an init script: https://gist.github.com/johncblandii/4757034.

unicorn.rb.erb

working_directory "<%= current_path %>"
pid "<%= unicorn_pid %>"
stderr_path "<%= unicorn_log %>"
stdout_path "<%= unicorn_log %>"

listen "/tmp/unicorn.<%= application %>.sock"
worker_processes <%= unicorn_workers %>
timeout 30

preload_app true

before_fork do |server, worker|
  # Disconnect since the database connection will not carry over
  if defined? ActiveRecord::Base
    ActiveRecord::Base.connection.disconnect!
  end

  # Quit the old unicorn process
  old_pid = "#{server.config[:pid]}.oldbin"
  if File.exists?(old_pid) && server.pid != old_pid
    begin
      Process.kill("QUIT", File.read(old_pid).to_i)
    rescue Errno::ENOENT, Errno::ESRCH
      # someone else did our job for us
    end
  end
end

after_fork do |server, worker|
  # Start up the database connection again in the worker
  if defined?(ActiveRecord::Base)
    ActiveRecord::Base.establish_connection
  end
end