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::Client.new(HEROKU_USERNAME, HEROKU_PASSWORD)
  end

  def stack
    heroku.list_stacks(HEROKU_APP_NAME).inject("") do |current,stack| 
      stack["current"] ? stack["name"] : current
    end
  end
  
  def get_workers
    if stack == "cedar"
      heroku.ps(HEROKU_APP_NAME).count { |p| p["process"] =~ /worker\.\d?/ }
    else
      heroku.info(HEROKU_APP_NAME)[:workers].to_i
    end
  end

  def set_workers(count)
    if stack == "cedar"
      heroku.ps_scale(HEROKU_APP_NAME, :type => 'worker', :qty => count)
    else
      heroku.set_workers(HEROKU_APP_NAME, count)
    end
  end
end

jobs.rb

# This gist is documented at http://ctoinsights.wordpress.com/2011/11/26/running-heroku-workers-only-when-required/
class GenericJob
  @@jobs_running = 0

  def initialize
    @@jobs_running += 1
    if Rails.env.production? and (@@jobs_running == 1)
      @heroku ||= HerokuManager.new
      @heroku.set_workers(1)
    end
  end

  def perform; end

  def after(job)
    @@jobs_running -= 1
    if Rails.env.production? and (@@jobs_running <=0)
      @heroku ||= HerokuManager.new
      @heroku.set_workers(0)
    end
  end

  def self.job_count
    @@jobs_running
  end
end

class TestJob < GenericJob
  def perform
    message = "#{Time.now} Test"
    puts message
  rescue Exception => e
    puts "#{Time.now} ERROR #{e.message}"
  end
end