Scheduler as worker

background_worker_starter.rb

class BackgroundWorkerStarter
  attr_reader :env

  def initialize(env)
    @env = env
  end

  def start!
    write_pid!(pid_file) if pid_file

    # This is supposed to be executed from the bash script directly, so do the heavy-lifting of loading env lazily
    require File.expand_path(File.join(File.dirname(__FILE__), '..', 'config', 'environment'))
    require_relative "./scheduler"

    # The very first worker also becomes a scheduler
    Scheduler.start! if worker_number == 0

    # 0, 1 etc
    case worker_number
    when 1 then run(queues: ['default', 'slow']) # worker #1 takes 'slow' queue
    else
      run(queues: ['default']) # Exclude 'slow' queue to have enough capacity if that one is very busy
    end
  end

  private

  def write_pid!(file)
    File.open(file, 'w') { |f| f << Process.pid }
  end

  def run(options={})
    # From https://github.com/collectiveidea/delayed_job/blob/master/lib/delayed/command.rb#L93
    Dir.chdir(Rails.root)
    Delayed::Worker.logger = Logger.new(File.join(Rails.root, 'log', 'delayed_job.log'))

    worker = Delayed::Worker.new(options)
    worker.name = worker_identifier
    worker.say "Worker with options is about to start: #{options.inspect}"
    worker.start
  rescue => e
    Rails.logger.fatal e
    STDERR.puts e.message
    exit 1
  end

  def pid_file
    env['PIDFILE']
  end

  def worker_identifier
    # /path/to/worker-1.pid => worker-1
    matching = pid_file.to_s.match(/([^\/]+)\.pid$/)
    matching ? matching[1] : 'not-available-0'
  end

  def worker_number
    worker_identifier.gsub(/\D/, '').to_i
  end
end

scheduler.rb

class Scheduler
  def initialize
    require 'rufus/scheduler'

    regularly do
      Jobs::RetireOverdueReservations.delay.run
      Jobs::NewReservationNotification.delay.run
      Jobs::CancelledReservationNotification.delay.run
    end

    nightly do
      Jobs::CleanupImports.delay.run
      Jobs::CleanupReports.delay.run
    end
  end

  def self.start!
    new.tap { |s| s.scheduler.start }
  end

  def scheduler
    @scheduler ||= Rufus::Scheduler::PlainScheduler.new(frequency: 0.5)
  end

  private

  def with_resources(&block)
    block.call
  ensure
    # The scheduler runs in a separate Thread thus AR opens a new connection.
    # So we need to make sure it gets closed at the end.
    ActiveRecord::Base.connection.close
  end

  def regularly(&block)
    # every 10 mins
    scheduler.every('10m') { with_resources(&block) }
  end

  def nightly(&block)
    # daily, 3am
    scheduler.cron("0 3 * * *") { with_resources(&block) }
  end
end

script-slash-worker

#!/usr/bin/env ruby
# encoding: utf-8

# For now, just preserving the ability to use monit from
# chef/custom_cookbooks/background_server/templates.default/monit.conf.erb

require_relative './../lib/background_worker_starter'
BackgroundWorkerStarter.new(ENV).start!