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Rainbows ActorSpawn AppPool Base Configurator Coolio CoolioThreadPool CoolioThreadSpawn DevFdResponse Epoll EventMachine FiberPool FiberSpawn MaxBody NeverBlock Rev RevFiberSpawn RevThreadPool RevThreadSpawn Revactor Sendfile ServerToken StreamResponseEpoll ThreadPool ThreadSpawn ThreadTimeout WriterThreadPool WriterThreadSpawn XEpoll XEpollThreadPool XEpollThreadSpawn

Rainbows! - unicorn for sleepy apps and slow clients

Rainbows! is an HTTP server for sleepy Rack applications. It is based on unicorn, but designed to handle applications that expect long request/response times and/or slow clients.

If you're on GNU/Linux and overwhelmed by options in Rainbows!, consider yahns as it has fewer options and more energy-efficient during non-peak traffic.

For Rack applications not heavily bound by slow external network dependencies, consider unicorn instead as it simpler and easier to debug.

If you're on a small system, or write extremely tight and reliable code and don't want multiple worker processes, check out Zbatery, too. Zbatery can use all the crazy network concurrency options of Rainbows! in a single worker process.

Rainbows! is about Diversity

We aim to support as many concurrency models as we can because they all suck; differently.

For network concurrency, models we currently support are:

We have many more on the way for handling network concurrency. Additionally, we also use multiple processes (managed by Unicorn) for robustness and CPU/memory/disk concurrency.

We also provide Rainbows::AppPool Rack middleware for some network concurrency models for limiting application concurrency independently of network concurrency.



Rainbows! is mainly designed for the odd things Unicorn sucks at:

Rainbows! can also be used to service slow clients directly even with fast applications.


Rainbows! is copyright 2009,2010 by all contributors (see logs in git). Rainbows! is licensed under the Ruby (1.8) license or the GPLv2 or later. See the included LICENSE file for more details.

Rainbows! is 100% Free Software.


You may install it via RubyGems on

gem install rainbows


for Rack applications

In APP_ROOT (where is located), run:


Rainbows! will bind to all interfaces on TCP port 8080 by default.

Configuration File(s)

Rainbows! will look for the file used by rackup in APP_ROOT.

For deployments, it can use a config file for Unicorn and Rainbows!-specific options specified by the --config-file/-c command-line switch. Rainbows! accepts all options found in Unicorn::Configurator as well as the "Rainbows!" block, so you can have the following in your config file:

worker_processes 4 # assuming four CPU cores
Rainbows! do
  use :FiberSpawn
  worker_connections 100

See the Rainbows! configuration documentation for more details.


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

git:// (mirror)

You may browse the code from the web and download the latest snapshot tarballs here:

Inline patches (from "git format-patch") to the mailing list are preferred because they allow code review and comments in the reply to the patch.

We will adhere to mostly the same conventions for patch submissions as git itself. See the Documentation/SubmittingPatches document distributed with git on on patch submission guidelines to follow. Just don't email the git mailing list or maintainer with Rainbows! patches.


There is NO WARRANTY whatsoever if anything goes wrong, but let us know and we'll try our best to fix it.


All feedback (bug reports, user/development discussion, patches, pull requests) go to the mailing list. Patches must be sent inline (git format-patch -M + git send-email). No subscription is necessary to post on the mailing list. No top posting. Address replies To: the mailing list.

We love to hear from you!
Email patches (using git send-email), pull requests (formatted using git request-pull), questions, bug reports, suggestions, etc. to us publically at:
Mail archives are available at:
Please send plain-text email only and do not waste bandwidth on HTML mail, HTML mail will not be read.
Quote as little as reasonable and do not top post.
For sensitive topics, email us privately at: