Running Heroku workers only when required

heroku_manager.rb

# This gist is documented at http://ctoinsights.wordpress.com/2011/11/26/running-heroku-workers-only-when-required/
class HerokuManager
  def heroku
    @heroku ||= Heroku::API.new
  end
  
  def get_workers
    heroku.get_ps(HEROKU_APP_NAME).body.count { |p| p["process"] =~ /worker\.\d?/ }
  end

  def set_workers(count)
    heroku.post_ps_scale(HEROKU_APP_NAME, 'worker', count)
  end
end 

jobs.rb

# This gist is documented at http://ctoinsights.wordpress.com/2011/11/26/running-heroku-workers-only-when-required/
class GenericJob

    def initialize
      if Rails.env.production?
        @heroku ||= HerokuManager.new
        @heroku.set_workers(1) if (@heroku.get_workers == 0)
      end 
    end
    
    def perform; end
    
    def after(job)
      if Rails.env.production?
        @heroku ||= HerokuManager.new
        @heroku.set_workers(0) if (job_count == 1)
      end
    end

    def job_count
      Delayed::Job.all(:conditions => {failed_at: nil}).length
    end
end
  
class TestJob < GenericJob
    def perform
      message = "#{Time.now} TestJob completed"
      puts message
    rescue Exception => e
      puts "#{Time.now} ERROR: #{e.message}"
    end
end