Run cron jobs on rails (deployed over several servers)

Question

What is the best way to run cron jobs on rails, when different machines have different jobs to do?

For example, server 1 runs cron job A, while server 2 runs cron job B

Is there a way to deploy the cron files along when we do a regular cap deploy?

Answer 1

take a look at the whenever gem, http://github.com/javan/whenever

It is great for automating cron tasks with rails with a clear DSL. We have been using it production for several months now and it just works and is very lightweight. Some examples from their README:

 every 3.hours do
    runner "MyModel.some_process"
    rake "my:rake:task"
    command "/usr/bin/my_great_command"
  end

  every 1.day, :at => '4:30 am' do
    runner "MyModel.task_to_run_at_four_thirty_in_the_morning"
  end

  every :hour do # Many shortcuts available: :hour, :day, :month, :year, :reboot
    runner "SomeModel.ladeeda"
  end

  every :sunday, :at => '12pm' do # Use any day of the week or :weekend, :weekday
    runner "Task.do_something_great"
  end

The README is very thorough, but there is also a good screencast on railscasts: http://railscasts.com/episodes/164-cron-in-ruby

It easily integrates with capistrano with the following code (copied from README):

  after "deploy:symlink", "deploy:update_crontab"

  namespace :deploy do
    desc "Update the crontab file"
    task :update_crontab, :roles => :db do
      run "cd #{release_path} && whenever --update-crontab #{application}"
    end
  end

As far as machine specific, you could use a local config file or even symlink the config/schedule.rb file on deploy. I think I would include a local file that would be symlinked on deploy local_schedule.rb and then put this at the top of the config/schedule.rb

if File.exists?(File.dirname(__FILE__) + '/config/local_schedule.rb')
  require File.dirname(__FILE__) + '/local_schedule.rb'
end

Your schedule would run but then include anything local, just make sure it is symlinked before the cap task above is run and you should be good to go.

I hope this helps!