Unicorn: Unix + LAN/localhost-only fork of Mongrel

Features

• Designed for Rack, Unix, fast clients, and ease-of-debugging. We cut out all things that are better-supported by nginx or Rack.
• Mostly written in Ruby, only the HTTP parser (stolen and trimmed down from Mongrel) is written in C. Unicorn is compatible with both Ruby 1.8 and 1.9. A pure-Ruby (but still Unix-only) version is planned.
• Process management: Unicorn will reap and restart workers that die from broken apps. There is no need to manage multiple processes or ports yourself. Unicorn can spawn and manage any fixed 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.
• Does not care if your application is thread-safe or not, workers all run within their own isolated address space and only serve one client at a time.
• Supports all Rack applications, along with pre-Rack versions of Ruby on Rails via a Rack wrapper.
• Builtin reopening of all log files in your application via USR1 signal. This allows logrotate to rotate files atomically and quickly via rename instead of the racy and slow copytruncate method. Unicorn also takes steps to ensure multi-line log entries from one request all stay within the same file.
• nginx-style binary re-execution without losing connections. You can upgrade Unicorn, your entire application, libraries and even your Ruby interpreter as long as Unicorn is installed in the same path.
• before_fork and after_fork hooks in case your application has special needs when dealing with forked processes. These should not be needed when the "preload_app" directive is false (the default).
• Can be used with copy-on-write-friendly memory management to save memory (by setting "preload_app" to true).
• Able to listen on multiple interfaces including UNIX sockets, each worker process can also bind to a private port via the after_fork hook for easy debugging.

License

Unicorn is copyright 2009 Eric Wong and contributors. It is based on Mongrel and carries the same license:

Mongrel is copyright 2007 Zed A. Shaw and contributors. It is licensed under the Ruby license and the GPL2. See the included LICENSE file for details.

Unicorn is 100% Free Software.

Install

The library consists of a C extension so you’ll need a C compiler or at least a friend who can build it for you.

You may download the tarball from the Mongrel project page on Rubyforge and run setup.rb after unpacking it:

rubyforge.org/frs/?group_id=1306

You may also install it via Rubygems on Rubyforge:

  gem install unicorn

You can get the latest source via git from the following locations (these versions may not be stable):

  git://git.bogomips.org/unicorn.git
  http://git.bogomips.org/unicorn.git
  git://repo.or.cz/unicorn.git (mirror)
  http://repo.or.cz/r/unicorn.git (mirror)

If you have web browser software for the World Wide Web (on the Information Superhighway), you may browse the code from your web browser and download the latest snapshot tarballs here:

• git.bogomips.org/cgit/unicorn.git (cgit)
• repo.or.cz/w/unicorn.git (gitweb)

Usage

non-Rails Rack applications

In APP_ROOT, run:

  unicorn

for Rails applications (should work for all 1.2 or later versions)

In RAILS_ROOT, run:

  unicorn_rails

Unicorn will bind to all interfaces TCP port 8080 by default. You may use the ’-l/—listen’ switch to bind to a different address:port or a UNIX socket.

Configuration File(s)

Unicorn will look for the config.ru file used by rackup in APP_ROOT.

For deployments, it can use a config file for Unicorn-specific options specified by the —config-file/-c command-line switch. See Unicorn::Configurator for the syntax of the Unicorn-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 `unicorn -h` or `unicorn_rails -h` to see command-line options.

Disclaimer

Like the creatures themselves, production deployments of Unicorn are rare or even non-existent. There is NO WARRANTY whatsoever if anything goes wrong, but let us know and we’ll try our best to fix it.

Unicorn is designed to only serve fast clients. See the PHILOSOPHY and DESIGN documents for more details regarding this.

Rainbows are NOT included.

Known Issues

• WONTFIX: code reloading with Sinatra 0.3.2 (and likely older versions) apps is broken. The workaround is to force production mode to disable code reloading in your Sinatra application:

    set :env, :production
  

  Since this is no longer an issue with Sinatra 0.9.x apps and only affected non-production instances, this will not be fixed on our end. Also remember we’re capable of replacing the running binary without dropping any connections regardless of framework :)

Contact

Email Eric Wong at normalperson@yhbt.net for now. Newsgroup and mailing list maybe coming…