god.config

# Based on example from <http://railscasts.com/episodes/130-monitoring-with-god>

# Use static root, as we're currently not reloading God config during deployments
APP_ROOT = '/var/www/twatcher/current'
APP_ENV = 'production'

def generic_monitoring(w, options = {})
  w.start_if do |start|
    start.condition(:process_running) do |c|
      c.interval = 10.seconds
      c.running = false
    end
  end
  
  w.restart_if do |restart|
    restart.condition(:memory_usage) do |c|
      c.above = options[:memory_limit]
      c.times = [3, 5] # 3 out of 5 intervals
    end
  
    restart.condition(:cpu_usage) do |c|
      c.above = options[:cpu_limit]
      c.times = 5
    end
  end
  
  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
    end
  end
end

God.watch do |w|
  w.name = "redis"
  #w.group = "redis"
  w.interval = 60.seconds
  w.start = "/usr/local/bin/redis-server #{APP_ROOT}/config/redis.conf"
  w.stop = "kill `cat /var/run/redis.pid`"
  w.start_grace = 10.seconds
  w.restart_grace = 10.seconds
  w.pid_file = "/var/run/redis.pid"
  
  w.behavior(:clean_pid_file)
  
  generic_monitoring(w, :cpu_limit => 30.percent, :memory_limit => 30.megabytes)
end

God.watch do |w|
  w.name = "twitter_filter"
  w.interval = 60.seconds
  # For some reason this only works when we first cd, then use a relative path. No idea why.
  w.start = "cd #{APP_ROOT}; RACK_ENV=#{APP_ENV} bin/twitter_filter.rb start"
  w.stop = "cd #{APP_ROOT}; RACK_ENV=#{APP_ENV} bin/twitter_filter.rb stop"
  w.start_grace = 10.seconds
  w.restart_grace = 10.seconds
  w.pid_file = "#{APP_ROOT}/log/twitter_filter.pid"
  
  w.behavior(:clean_pid_file)
  
  generic_monitoring(w, :cpu_limit => 30.percent, :memory_limit => 50.megabytes)
end

twitter_filter.rb

# I'm using the Daemons gem to daemonize the app. Will share the whole app soon, but basically like this:

daemon_options = {
  :dir_mode => :normal,
  :dir => File.join(File.dirname(__FILE__), '..', 'log'),
  :log_output => true
}

 Daemons.run_proc('twitter_filter', daemon_options) do
   # Actual twitter filter code goes here
 end