Today I wanted to write a script which could be used to start/stop/restart unicorn for a given application – without root privileges, to get a status and a special action(monitor) which can be called periodically and will restart unicorn automatically in case something went wrong

I found this very usefull blogpost on the net http://rubynyc.wordpress.com/2009/12/24/unicorn-scriptspin/ and modified the script with 2 additional “methods”: status and monitor. (I know … the code I added is pretty primitive… but it works)


#!/usr/local/bin/ruby

class Runner
class << self def start system "cd #{APP_PATH}; #{UNICORN_RAILS} -c ./config/unicorn.rb -E production -D" end def reload system "kill -s USR2 #{pid}" end def restart stop start end def graceful_stop system "kill -s QUIT #{pid}" end def stop system "kill #{pid}" end def pid File.read "#{APP_PATH}/tmp/pids/unicorn.pid" end def status begin system "ps -o user,pid,ppid,command -ax | grep #{pid}" rescue puts 'not started' end end #start if killed def monitor begin #this throws an exception in 2 cases: #1. if no unicorn-process for the current user exists #2. if the pid functions fails(throws an error) due to non-existant unicorn.pid-file throw 'processes killed manually' if (`ps -o user,pid,ppid,command -ax | grep #{pid}`).split("\n").size <= 2 rescue puts 'restarting ... ' start end end end end case ARGV[1] when "start" Runner.start when "reload" Runner.reload when "restart" Runner.restart when "stop" Runner.stop when "status" Runner.status when "monitor" Runner.monitor else STDERR.puts "usage ./unicorn_script.rb absolute_path_to_RAILS_ROOT [start|stop|restart|status|monitor]" exit(1) end

This script can be called from a cron every minute like this


* * * * * /path/to/this_script /path/to/rails_root/ monitor


It baiscally checks if the unicorn-processes exist(the master process and his spawned kids). If it does not detect at least one unicorn-process it will calls the start routine.