Setting up DelayedJob Workers on Heroku using DataMapper hooks

heroku_dj.rb

if ENV["HEROKU_APP"]  
  # Spin-up workers when jobs are created
  Delayed::Job.after :create do
    workers_needed = [Delayed::Job.count + 1, MAX_CONCURRENT_WORKERS].min
    @username = ENV['HEROKU_USERNAME']
    @password = ENV['HEROKU_PASSWORD']
    @app = ENV['HEROKU_APP']
    client = Heroku::Client.new(@username, @password)
    client.set_workers(@app, workers_needed)
    puts "- Initialized Heroku workers for ZipDecoder"    
  end
  
  # Spin-down workers as jobs destroyed
  Delayed::Job.after :destroy do
    workers_needed = [Delayed::Job.count - 1, 0].max
    client = Heroku::Client.new(@username, @password)
    client.set_workers(@app, workers_needed)
    puts "- Cleaned Up a Delayed Job for ZipDecoder"
  end
end