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pitchfork: Rack HTTP server for shared-nothing architecture

pitchfork is a preforking HTTP server for Rack applications designed to minimize memory usage by maximizing Copy-on-Write performance.

Like unicorn (of which pitchfork is a derivative), it is designed to only serve fast clients on low-latency, high-bandwidth connections and take advantage of features in Unix/Unix-like kernels. Slow clients should only be served by placing a reverse proxy capable of fully buffering both the request and response in between pitchfork and slow clients.


Until this notice is removed from the README, pitchfork should be considered experimental. As such it is not encouraged to run it in production just yet unless you feel capable of debugging yourself any issue that may arise.


  • Designed for Rack, Linux, fast clients, and ease-of-debugging. We cut out everything that is better supported by the operating system, nginx or Rack.

  • Shared-Nothing architecture: workers all run within their own isolated address space and only serve one client at a time for maximum performance and robustness. Concurrent requests don't need to compete for the GVL, or impact each others latency when triggering garbage collection. It also does not care if your application is thread-safe or not.

  • Reforking: pitchfork can be configured to periodically promote a warmed up worker as the new template from which workers are forked. This dramatically improves the proportion of shared memory, making processes use only marginally more memory than threads would.

  • Compatible with Ruby 2.5.0 and later.

  • Process management: pitchfork will reap and restart workers that die from broken apps. There is no need to manage multiple processes or ports yourself. pitchfork can spawn and manage any number of worker processes you choose to scale to your backend.

  • Load balancing is done entirely by the operating system kernel. Requests never pile up behind a busy worker process.


Ruby(MRI) Version 2.5 and above.

pitchfork can be used on any Unix-like system, however the reforking feature requires PR_SET_CHILD_SUBREAPER which is a Linux 3.4 (May 2012) feature.


Add this line to your application's Gemfile:

gem "pitchfork"

And then execute:

$ bundle install

Or install it yourself as:

$ gem install pitchfork



In your application root directory, run:

$ bundle exec pitchfork

pitchfork will bind to all interfaces on TCP port 8080 by default. You may use the --listen switch to bind to a different address:port or a UNIX socket.

Configuration File(s)

pitchfork will look for the file used by rackup in APP_ROOT.

For deployments, it can use a config file for pitchfork-specific options specified by the --config-file/-c command-line switch. See the configuration documentation for the syntax of the pitchfork-specific options.

The default settings are designed for maximum out-of-the-box compatibility with existing applications.

Most command-line options for other Rack applications (above) are also supported. Run pitchfork -h to see command-line options.

Relation to Unicorn

Pitchfork initially started as a Unicorn patch, however some of Unicorn features as well as Unicorn policy of supporting extremely old Ruby version made it challenging.

Forking was the occasion to significantly reduce the complexity.

However some large parts of Pitchfork like the HTTP parser are still mostly unchanged from Unicorn, and Unicorn is fairly stable these days. As such we aim to backport any Unicorn patches that may apply to Pitchfork and vice versa.


pitchfork is copyright 2022 Shopify Inc and all contributors. It is based on Unicorn 6.1.0.

Unicorn is copyright 2009-2018 by all contributors (see logs in git). It is based on Mongrel 1.1.5. Mongrel is copyright 2007 Zed A. Shaw and contributors.

pitchfork is licensed under the GPLv2 or later or Ruby (1.8)-specific terms. See the included LICENSE file for details.


Thanks to Eric Wong and all Unicorn and Mongrel contributors over the years. Pitchfork would have been much harder to implement otherwise.

Thanks to Will Jordan who implemented Puma's "fork worker" experimental feature which have been a significant inspiration for Pitchfork.

Thanks to Peter Bui for letting us use the pitchfork name on Rubygems.


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