Resque Pool

Resque pool is a simple library for managing a pool of resque workers. Given a a config file, it manages your workers for you, starting up the appropriate number of workers for each.

Benefits

• Less config - With a simple YAML file, you can start up a pool daemon, and it will monitor your workers for you. An example init.d script, monit config, and chef cookbook are provided.
• Less memory - If you are using Ruby Enterprise Edition, or any ruby with copy-on-write safe garbage collection, this should save you a lot of memory when you are managing many workers.
• Faster startup - when you start many workers at once, they would normally compete for CPU as they load their environments. Resque-pool can load the environment once and fork all of the workers almost instantly.

How to use

YAML file config

Create a config/resque-pool.yml (or resque-pool.yml) with your worker counts. The YAML file supports both using root level defaults as well as environment specific overrides (RACK_ENV, RAILS_ENV, and RESQUE_ENV environment variables can be used to determine environment). For example in config/resque-pool.yml:

foo: 1
bar: 2
"foo,bar,baz": 1

production:
  "foo,bar,baz": 4

Rake task config

Require the rake tasks (resque/pool/tasks) in your Rakefile, load your application environment, configure Resque as necessary, and configure resque:pool:setup to disconnect all open files and sockets in the pool manager and reconnect in the workers. For example, with rails you should put the following into lib/tasks/resque.rake:

require 'resque/pool/tasks'
# this task will get called before resque:pool:setup
# and preload the rails environment in the pool manager
task "resque:setup" => :environment do
  # generic worker setup, e.g. Hoptoad for failed jobs
end
task "resque:pool:setup" do
  # close any sockets or files in pool manager
  ActiveRecord::Base.connection.disconnect!
  # and re-open them in the resque worker parent
  Resque::Pool.after_prefork do |job|
    ActiveRecord::Base.establish_connection
  end
end

Start the pool manager

Then you can start the queues via:

resque-pool --daemon --environment production

This will start up seven worker processes, one exclusively for the foo queue, two exclusively for the bar queue, and four workers looking at all queues in priority. With the config above, this is similar to if you ran the following:

rake resque:work RAILS_ENV=production QUEUES=foo &
rake resque:work RAILS_ENV=production QUEUES=bar &
rake resque:work RAILS_ENV=production QUEUES=bar &
rake resque:work RAILS_ENV=production QUEUES=foo,bar,baz &
rake resque:work RAILS_ENV=production QUEUES=foo,bar,baz &
rake resque:work RAILS_ENV=production QUEUES=foo,bar,baz &
rake resque:work RAILS_ENV=production QUEUES=foo,bar,baz &

The pool manager will stay around monitoring the resque worker parents, giving three levels: a single pool manager, many worker parents, and one worker child per worker (when the actual job is being processed). For example, ps -ef f | grep [r]esque (in Linux) might return something like the following:

resque    13858     1  0 13:44 ?        S      0:02 resque-pool-manager: managing [13867, 13875, 13871, 13872, 13868, 13870, 13876]
resque    13867 13858  0 13:44 ?        S      0:00  \_ resque-1.9.9: Waiting for foo
resque    13868 13858  0 13:44 ?        S      0:00  \_ resque-1.9.9: Waiting for bar
resque    13870 13858  0 13:44 ?        S      0:00  \_ resque-1.9.9: Waiting for bar
resque    13871 13858  0 13:44 ?        S      0:00  \_ resque-1.9.9: Waiting for foo,bar,baz
resque    13872 13858  0 13:44 ?        S      0:00  \_ resque-1.9.9: Forked 7481 at 1280343254
resque     7481 13872  0 14:54 ?        S      0:00      \_ resque-1.9.9: Processing foo since 1280343254
resque    13875 13858  0 13:44 ?        S      0:00  \_ resque-1.9.9: Waiting for foo,bar,baz
resque    13876 13858  0 13:44 ?        S      0:00  \_ resque-1.9.9: Forked 7485 at 1280343255
resque     7485 13876  0 14:54 ?        S      0:00      \_ resque-1.9.9: Processing bar since 1280343254

Running as a daemon will default to placing the pidfile and logfiles in the conventional rails locations, although you can configure that. See resque-pool --help for more options.

SIGNALS

The pool manager responds to the following signals:

• HUP - reload the config file, e.g. to change the number of workers per queue list
• QUIT - send QUIT to each worker parent and shutdown the manager after all workers are done.
• INT - send QUIT to each worker parent and immediately shutdown manager
• TERM - send TERM to each worker parent and immediately shutdown manager
• WINCH - send QUIT to each worker, but keep manager running (send HUP to reload config and restart workers)
• USR1/USR2/CONT - send the signal on to all worker parents (see Resque docs).

After a HUP, workers that are no longer needed will be gracefully shutdown via QUIT.

Other Features

An example chef cookbook is provided (and should Just Work at Engine Yard as is; just provide a /data/#{app_name}/shared/config/resque-pool.yml on your utility instances). Even if you don't use chef you can use the example init.d and monitrc erb templates in examples/chef_cookbook/templates/default.

You can also start a pool manager via rake resque:pool or from a plain old ruby script by calling Resque::Pool.run.

Workers will watch the pool manager, and gracefully shutdown (after completing their current job) if the manager process disappears before them.

You can specify an alternate config file by setting the RESQUE_POOL_CONFIG or with the --config command line option.

TODO

See the TODO list at github issues.

Contributors

• John Schult (config file can be split by environment)
• Stephen Celis (increased gemspec sanity)
• Vincent Agnello, Robert Kamunyori, Paul Kauders; for pairing with me at B'more on Rails Open Source Hack Nights. :)