Rails application rackup use unicorn_rails with god.

application.god

# http://god.rubyforge.org/
# http://unicorn.bogomips.org/SIGNALS.html
# http://railscasts.com/episodes/130-monitoring-with-god

rails_env = ENV['RAILS_ENV'] || 'production'
rails_appname = ENV['RAILS_APPNAME'] || 'myapp'
rails_root = ENV['RAILS_ROOT'] || "/opt/deploy/#{rails_appname}/current"

def generic_monitoring(w, options = {})
# generic_monitoring option list
# option list
# [:start_grace], [:stop_grace], [:restart_grace]
# [:cpu_interval], [:cpu_limit], [:memory_interval], [:memory_limit], [:contact]

  w.start_grace   = options[:start_grace]
  w.stop_grace    = options[:stop_grace]
  w.restart_grace = options[:restart_grace]

  # determine the state on startup
  w.transition(:init, { true => :up, false => :start }) do |on|
    on.condition(:process_running) do |c|
      c.running = true
      c.notify  = options[:contact]
    end
  end

  # determine when process has finished starting
  w.transition([:start, :restart], :up) do |on|
    on.condition(:process_running) do |c|
      c.running = true
      c.notify  = options[:contact]
    end
    
    # failsafe
    on.condition(:tries) do |c|
      c.times = 5
      c.transition = :start
      c.notify  = options[:contact]
    end
  end


  # start if process is not running
  w.transition(:up, :start) do |on|
    on.condition(:process_exits) do |c|
      c.notify  = options[:contact]
    end
  end

  # restart if memory or cpu is too high
  w.transition(:up, :restart) do |on|
    on.condition(:memory_usage) do |c|
      c.interval = options[:memory_interval]
      c.above = options[:memory_limit]
      c.times = [3, 5]
      c.notify  = options[:contact]
    end
    
    on.condition(:cpu_usage) do |c|
      c.interval = options[:cpu_interval]
      c.above = options[:cpu_limit]
      c.times = [3, 5]
      c.notify  = options[:contact]
    end
  end

  # lifecycle
  w.lifecycle do |on|
    on.condition(:flapping) do |c|
      c.to_state = [:start, :restart]
      c.times = 5
      c.within = 5.minute
      c.transition = :unmonitored
      c.retry_in = 10.minutes
      c.retry_times = 5
      c.retry_within = 2.hours
      c.notify  = options[:contact]
    end
  end

end


God.watch do |w|
  w.name = "#{rails_appname}_unicorn"
  w.group = "#{rails_appname}"
  w.interval = 5.seconds
  w.dir = rails_root
  w.pid_file = File.join(rails_root, "/tmp/pids/unicorn.pid")

  w.env      = {
    "HOME" => "/root"
  }

  # unicorn needs to be run from the rails root
  w.start = "bundle exec unicorn_rails -c config/#{rails_appname}_unicorn.rb -E #{rails_env} -D"

  # QUIT gracefully shuts down workers
  w.stop_signal = 'QUIT'

  # USR2 causes the master to re-create itself and spawn a new worker pool
  # or god signal USR2 #{app}
  w.restart = "kill -USR2 `cat #{w.pid_file}`"

  w.uid = 'root'
  w.gid = 'root'

  w.behavior(:clean_pid_file)

  # generic_monitoring option list
  # [:start_grace], [:stop_grace], [:restart_grace]
  # [:cpu_interval], [:cpu_limit], [:memory_interval], [:memory_limit], [:contact]
  generic_monitoring(w,
                     :start_grace =>      10.seconds,
                     :stop_grace =>       10.seconds,
                     :restart_grace =>    10.seconds,
                     :cpu_interval =>     60.seconds,
                     :cpu_limit =>        80.percent,
                     :memory_interval =>  60.seconds,
                     :memory_limit =>    200.megabytes,
                     :contact =>          'mailto',
                    )

end

god.conf

God::Contacts::Email.defaults do |d|
  d.to_email = %w{"user01@example.com", "user02@example.com"}
  d.to_name           = "myApp Developers"
  d.from_email        = "appserver@example.com"
  d.from_name         = "god"

  d.delivery_method   = :smtp
  d.server_host     = "127.0.0.1"
end

God.contact(:email) do |c|
  c.name     = 'mailto'
end

God.load "/usr/local/etc/god.d/*.god"