#async_observer

For one of our projects, we’re using beanstalkd in combination with the async_observer plugin for Rails to run slow tasks in the background.

This is a nice setup. Although we’re not using all of its more advanced features, beanstalkd is a very powerful and efficient queueing system, and async_observer provides a clean integration with Rails. (On other projects, I’ve happily used delayed_job for similar purposes, but it was not suitable for this project due to its heavy dependency on a ActiveRecord and a SQL database. By contrast, async_observer’s support for ActiveRecord was quite easy to rip out.)

However, we would like to be able to queue async_observer jobs from cron or the command line. Why launch a new process with a copy of the Rails stack when there’s already a long-lived one running? So, I wrote a ruby script with minimal dependencies which can stick tasks in beanstalkd for our async_observer worker to run.

The Script

Here’s the script I wrote. Stick it in RAILS_ROOT/script/beanstalk-queue.

1 #!/usr/bin/env ruby 2 3 # 4 # == Synopsis 5 # 6 # This is a replacement for script/runner which avoids loading up the 7 # rails environment and instead queues things for async_observer to 8 # do. Note that, unlike script/runner, a filename is not accepted; you 9 # must provide the code to run on the command-line. 10 # 11 # == Usage 12 # 13 # beanstalk-queue [OPTION] ... 'CODE' 14 # 15 # -d DELAY: 16 # amount of delay before the job is run (default 0 seconds) 17 # 18 # -e ENVIRONMENT: 19 # set the rails environment (falls back to ENV['RAILS_ENV'] or 20 # 'development' if unset) 21 # 22 # -p PRIORITY: 23 # set the job priority (default 65536) 24 # 25 # -t TTR: 26 # set the job's time to run (default 120 seconds) 27 # 28 # -v, --verbose: 29 # be verbose 30 # 31 # -h, --help: 32 # display this help 33 # 34 # CODE: the ruby code to be called asynchronously 35 # 36 37 require 'rubygems' 38 39 require 'beanstalk-client' 40 require 'getoptlong' 41 require 'rdoc/usage' 42 require 'yaml' 43 44 RAILS_ROOT = File.expand_path(File.join(File.dirname(__FILE__), "..")) 45 46 opts = GetoptLong.new( 47 ['--help', '-h', GetoptLong::NO_ARGUMENT], 48 ['-d', GetoptLong::REQUIRED_ARGUMENT], 49 ['-e', GetoptLong::REQUIRED_ARGUMENT], 50 ['-p', GetoptLong::REQUIRED_ARGUMENT], 51 ['-t', GetoptLong::REQUIRED_ARGUMENT], 52 ['--verbose', '-v', GetoptLong::NO_ARGUMENT] 53 ) 54 55 pool = Beanstalk::Pool.new(%w(localhost:11300)) 56 57 tube = 'default' 58 delay = 0 59 environment = ENV['RAILS_ENV'] || 'development' 60 priority = 65536 61 ttr = 120 62 verbose = false 63 64 opts.each do |opt,arg| 65 case opt 66 when '--help' 67 RDoc::usage 68 when '-d' 69 delay = arg.to_i 70 when '-e' 71 environment = arg 72 when '-p' 73 priority = arg.to_i 74 when '-t' 75 ttr = arg.to_i 76 when '--verbose' 77 verbose = true 78 end 79 end 80 81 if ARGV.length != 1 82 $stderr.puts "missing code to run (try #{File.basename(__FILE__)} --help)\n" 83 exit 1 84 end 85 86 code = ARGV[0] 87 88 case environment 89 when 'production' 90 if File.exist?(File.join(RAILS_ROOT, "REVISION")) 91 tube = File.read(File.join(RAILS_ROOT, "REVISION")).strip 92 end 93 when 'development' 94 tube = 'ourproj-development' 95 end 96 97 puts "using tube #{tube}" if verbose 98 99 pool.connect 100 pool.use(tube) 101 job = YAML.dump({:type => :rails, :code => code}) 102 103 puts "job:", job if verbose 104 105 job_id = pool.put(job, priority, delay, ttr) 106 107 puts "job #{job_id} sent to #{pool.last_server}" if verbose

Download this code.

Usage

Because this code does not load Rails or your application, it is unfortunately unable to determine how you have configured your application. Therefore, you must configure the script itself.

First, if you’re not using the default beanstalkd configuration of one server running on localhost:11300, edit line 55 appropriately. Next, you’re probably not using the same beanstalkd tube naming convention as we are, so edit lines 88–95 to properly map rails environment names to beanstalkd tube names.

Full documentation for running the script is at the top of the file, or run script/beanstalk-queue --help, but basically it works like script/runner with some extra optional parameters for controlling the queueing:

$ ./script/beanstalk-queue -e production 'MyModel.some_long_task'

cron and whenever integration

If you use whenever for dealing with programatically your crontab file, here’s a bit of code to define a new beanstalk job type, analogous to the runner job type:

1 module ::Whenever 2 module Job 3 class Beanstalk < Whenever::Job::Default 4 def output 5 path_required 6 %Q(#{File.join(@path, 'script', 'beanstalk-queue')} -e #{@environment} #{task.inspect}) 7 end 8 end 9 end 10 11 class JobList 12 def beanstalk(task, options = {}) 13 options.reverse_merge!(:environment => @environment, :path => @path) 14 options[:class] = Whenever::Job::Beanstalk 15 command(task, options) 16 end 17 end 18 end

Download this code.