Heroku Autoscale + Min and Max Workers

heroku_autoscale.rb

# Inspired by https://gist.github.com/1332883

module HerokuAutoscale
  module Scaler
    class << self
      @@heroku = Heroku::Client.new( ENV['HEROKU_USER'], ENV['HEROKU_PASS'] )

      def workers
        @@heroku.info(ENV['HEROKU_APP'])[:workers].to_i
      end

      def workers=( qty )
        min_workers = ENV["MIN_WORKERS"].to_i 
        max_workers = ENV["MAX_WORKERS"].to_i 

        @@heroku.set_workers(ENV['HEROKU_APP'], qty) unless qty < min_workers || qty > max_workers
      end

      def increment_workers( increment = 1 )
        new_total = workers() + increment
        @@heroku.set_workers(ENV["HEROKU_APP"], new_total ) unless new_total > ENV["MAX_WORKERS"].to_i
      end

      def decrement_workers( decrement = 1 )
        new_total = workers() - decrement
        @@heroku.set_workers(ENV["HEROKU_APP"], new_total ) unless new_total < ENV["MIN_WORKERS"].to_i
      end

      def job_count
        # Searching for jobs that where not locked
        Delayed::Job.count
      end

      def jobs_in_progress
        in_progress = 0
        Delayed::Job.all.each{|dj| in_progress += 1 if dj.locked_by != nil }
        return in_progress
      end
    end
  end

  def after_perform_scale_down
    Scaler.workers = 0
  end

  def after_enqueue_scale_up
    Scaler.workers = 1
  end

  def scale_up
    Scaler.increment_workers( 1 )
  end

  def scale_down
    Rails.logger.info( "[MF] Job Count for scale_down =>"+ Scaler.job_count.to_s )
    in_progress = Scaler.jobs_in_progress

    Scaler.workers = ENV["MIN_WORKERS"].to_i + in_progress
  end

end