gistfile1.rb

# Setup the following in your heroku config vars:
# See http://blog.leshill.org/blog/2010/11/02/heroku-environment-variables.html for an idea on how to do it
    HEROKU_APP: poh-dev
    HEROKU_USER: [email protected]
    HEROKU_PASSWORD: replace_me

# Gemfile
gem 'heroku', '>= 1.19.1'
gem 'resque'
# Use our fork until our fix is merged.
# https://github.com/bvandenbos/resque-scheduler/pull/68
gem 'resque-scheduler', require: 'resque_scheduler', git: 'git://github.com/infbio/resque-scheduler', ref: 'strings_with_hooks'

# config/initializers/resque.rb
Resque.schedule = YAML.load_file(File.join(File.dirname(__FILE__), '../resque_schedule.yml'))
Resque.after_fork = Proc.new { ActiveRecord::Base.establish_connection }

# lib/tasks/resque.rake
require 'resque/tasks'
require 'resque_scheduler/tasks'

module ResqueWorker
  extend self

  def scheduler_or_worker?
    redis = Resque.redis
    if redis.setnx('scheduler_active', 'active')
      begin
        yield 'scheduler'
      ensure
        redis.del('scheduler_active')
      end
    else
      yield 'work'
    end
  end
end

task "resque:setup" => :environment
task "resque:scheduler_setup" => :environment # load the env so we know about the job classes


desc "Run Resque workers on Heroku"
task "jobs:work" => ["resque:setup", "resque:scheduler_setup"] do
  ENV['QUEUE'] = '*'
  ResqueWorker.scheduler_or_worker? {|which| Rake::Task["resque:#{which}"].invoke }
end

# NB include this in your Job models i.e.
#
# class NotificationTime < ActiveRecord::Base
#   extend HerokuResqueAutoscale
# ...
#
# app/models/heroku_resque_autoscale
require 'heroku'

module HerokuResqueAutoscale
  module Scaler
    extend self

    def heroku
      if ENV['HEROKU_USER'] && ENV['HEROKU_PASSWORD'] && ENV['HEROKU_APP']
        @heroku ||= Heroku::Client.new(ENV['HEROKU_USER'], ENV['HEROKU_PASSWORD'])
      else
        false
      end
    end

    def workers
      if heroku
        heroku.info(ENV['HEROKU_APP'])[:workers].to_i
      else
        0
      end
    end

    def workers=(qty)
      heroku.set_workers(ENV['HEROKU_APP'], qty) if heroku
    end

    def job_count
      Resque.info[:pending].to_i
    end
  end

  def scale_down!
    # Nothing fancy, just shut everything but the scheduler down if we have no jobs
    Scaler.workers = 1 if Scaler.job_count.zero?
  end

  def after_perform_scale_down(*args)
    scale_down!
  end

  def after_enqueue_scale_up(*args)
    [
      { :workers => 2, # This many workers
        :job_count => 1 # For this many jobs or more, until the next level
      },
      { :workers => 3,
        :job_count => 15
      },
      { :workers => 4,
        :job_count => 25
      },
      { :workers => 5,
        :job_count => 40
      },
      { :workers => 6,
        :job_count => 60
      }
    ].reverse_each do |scale_info|
      # Run backwards so it gets set to the highest value first
      # Otherwise if there were 70 jobs, it would get set to 1, then 2, then 3, etc

      # If we have a job count greater than or equal to the job limit for this scale info
      if Scaler.job_count >= scale_info[:job_count]
        # Set the number of workers unless they are already set to a level we want. Don't scale down here!
        if Scaler.workers <= scale_info[:workers]
          Scaler.workers = scale_info[:workers]
        end
        break # We've set or ensured that the worker count is high enough
      end
    end
  end

  def on_failure(e, *args)
    Rails.logger.info("Resque Exception for [#{self.to_s}, #{args.join(', ')}] : #{e.to_s}")
    scale_down!
  end
end