capistrano task to deal with unicorn restarts during deployment

unicorn_cap_task.rb

namespace :unicorn do
  
  desc "Zero-downtime restart of Unicorn"
  task :restart, :except => { :no_release => true } do
    # you can use this signal if preload_app ==  false
    # run "kill -s HUP `cat #{shared_path}/pids/unicorn.pid`"   

    # use this signal if preload_app ==  true
    run "kill -s USR2 `cat #{shared_path}/pids/unicorn.pid`" 
    # give unicorn some seconds to create unicorn.pid.oldbin
    sleep 3
    # see processes:
    run "ps aux | grep 'unicorn master'"
    run "kill -s QUIT `cat #{shared_path}/pids/unicorn.pid.oldbin`"
  end

  desc "Start unicorn"
  task :start, :except => { :no_release => true } do
    run "cd #{current_path}; RAILS_ENV=#{rails_env} bundle exec unicorn -c config/unicorn.rb -D -E #{rails_env}"
  end

  desc "Stop unicorn"
  task :stop, :except => { :no_release => true } do
    run "kill -s QUIT `cat #{shared_path}/pids/unicorn.pid`"
  end
end