http://pablocantero.com/blog/2013/04/02/monit-restarts-unicorn-usr2-you-are-doing-it-wrong/

app

# /etc/nginx/sites-available/app

upstream app_server {
        server unix:/tmp/.unicorn_app.sock fail_timeout=0;
}

server {
        listen 80;
        server_name app.com;

        location / {
                proxy_pass http://app_server;
                proxy_set_header Host $host;
                proxy_redirect off;
        }
}

app.conf

# /etc/monit/conf.d/app.conf
check process app with pidfile /home/ubuntu/app/shared/pids/unicorn.pid
   stop program  = "/bin/su - ubuntu -c '/home/ubuntu/unicorn-stop.sh'"  with timeout 60 seconds
   start program = "/bin/su - ubuntu -c '/home/ubuntu/unicorn-start.sh'" with timeout 60 seconds

unicorn-restart.sh

#!/bin/bash

pkill -USR2 -f unicorn_rails.*master

exit 0

unicorn-start.sh

#!/bin/bash

cd /home/ubuntu/app/current
export GEM_HOME=/home/ubuntu/.rvm/gems/ruby-1.9.3-p286@global/
export RAILS_ENV=production
export PATH=/home/ubuntu/.rvm/rubies/ruby-1.9.3-p286/bin/:/home/ubuntu/.rvm/gems/ruby-1.9.3-p286/bin/:$PATH
/home/ubuntu/.rvm/gems/ruby-1.9.3-p286@global/bin/bundle exec unicorn_rails -p 9000 -c /home/ubuntu/app/current/config/unicorn.conf.rb -D

exit 0

unicorn-stop.sh

#!/bin/bash

pkill -f unicorn_rails.*master

exit 0

unicorn.conf.rb

# app/current/config/unicorn.conf.rb
# -*- encoding : utf-8 -*-
# Unicorn configuration file

listen "/tmp/.unicorn_app.sock", :backlog => 64
worker_processes 3
pid "/home/ubuntu/app/shared/pids/unicorn.pid"
stderr_path "/home/ubuntu/app/log/vitrine-error.log"
stdout_path "/home/ubuntu/app/log/vitrine.log"
timeout 30

preload_app true

before_fork do |server, worker|
  # stops old master
  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
    end
  end

  ActiveRecord::Base.connection.disconnect! if defined?(ActiveRecord::Base)
end

after_fork do |server, worker|
  ActiveRecord::Base.establish_connection if defined?(ActiveRecord::Base)
  ::NewRelic::Agent.after_fork(:force_reconnect => true) if defined? Unicorn
end