\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. For Rack applications not heavily bound by slow external network dependencies, consider Unicorn instead as it simpler and easier to debug.
Gemfile gem 'rainbows', '~> 0.93.0'
install gem install rainbows -v 0.93.0