= Unicorn: Unix + LAN/localhost-only fork of Mongrel
* 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
* 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.
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
Unicorn is 100% Free Software.
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:
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):
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:
* http://git.bogomips.org/cgit/unicorn.git (cgit)
* http://repo.or.cz/w/unicorn.git (gitweb)
=== non-Rails Rack applications
In APP_ROOT, run:
=== for Rails applications (should work for all 1.2 or later versions)
In RAILS_ROOT, run:
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
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 :)
Email Eric Wong at email@example.com for now.
Newsgroup and mailing list maybe coming...