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Rack proxy server for development
Ruby Shell C HTML Makefile
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A pure Ruby alternative to Pow!!

Aka a Rack application spawner and proxy for simpler local development. Calling and with no configuration is simpler than editing your hosts file, starting your applications manually on port 3000, etc.

Development State

Prax isn't under active development anymore. Most features have been implemented and are working (unless there are installation or configuration problems). I'm doing my best to maintain Prax as much as I can and to answer questions and troubleshoots in the issues.

Yet, most of my development efforts have been focused on a port to the Crystal programming language, a Ruby-like language that compiles down to binary code using LLVM, which should help reduce a bunch of problems related to version managers and per-project rubies conflicting with the Ruby that Prax runs in —but comes with its own problems like complexity of debugging a segfault in release mode.

Please check Prax (Crystal port) if you are interested or have too much problems installing/configuring the Ruby version of Prax.


My GNU/Linux fork of Pow just broke on me badly, and I couldn't read, less write the coffeescript it's written in. I thus decided to try writing an alternative in Ruby. Good for me, because I now have a viable alternative, and learned a lot about TCP and UNIX sockets, the HTTP protocol, Rack and Ruby Threads.

Also, Prax only requires Ruby and the Rack gem, both you should have already installed if you are a Ruby Web developer.


Prax has been developed with MRI Ruby 1.9.3 and newer, but should be compatible with most Ruby engines like Rubinius 2+ and JRuby 1.7+ in 1.9 modes. Ruby 1.8 is deprecated, and no longer supported.

Installing on GNU/Linux

First clone the repository somewhere (like /opt or /usr/local/lib), and run the installer which will install the port forwarding script and NSSwitch extension:

$ git clone git:// /opt/prax
$ cd /opt/prax/ && ./bin/prax install

Now link your applications:

$ cd ~/Work/myapp
$ prax link

Point your browser to and wait for your Rack application to spawn.

To install Prax manually, or to review the installation process, please look at the prax-install script.

Ruby Version Managers

Prax being written in Ruby, version managers usually have problems to select the correct version of Ruby or gemset (for RVM) to run Prax and to run your Rack applications. You must configure Prax to handle your version manager correctly.

Start Prax automatically

You may want to create a prax.desktop file in ~/.config/autostart so that Prax will be started automatically when GNOME starts for example. Please see with your desktop environment which solution works best.

If you don't use X, you may add a prax start line to your ~/.bashrc for example, but be aware that it will restart Prax (and all Rack instances) everytime you log in. That could be fixed with a --no-restart flag and a status command (contributions welcome).


If you experience some regular slowness, where Prax seems to hang for periods of 5 seconds, this is because of the DNS resolution: NSSwitch tries a real DNS resolution before checking the prax extension. This usually creates an overhead of less than half a second, but sometimes takes 5 seconds on my Ubuntu 12.04.

You may try to move the prax NSSwitch extension before the dns one, so it looks like this:

hosts: files mdns4_minimal [NOTFOUND=return] prax dns mdns4

This will dramatically speed up the DNS resolution of *.dev domains, and it should never hang anymore, BUT please be aware that it may cause problems in regular DNS resolutions (it works correctly for me).

Mac OS X

Mac OS X isn't supported yet. Feel free to contribute!


This is an ever going work in progress, thought Prax isn't missing much things to be on par with Pow! The current features have been implemented:

  • HTTP Server

  • HTTP Proxy

  • HTTP Port Forwarding

  • SSL support (if certs and keys are generated)

  • Rack Handler (Racker)

  • Rack Application spawn, restart, always restart and autokill

  • Export ENV vars from a myapp/.env file

  • Source ~/.praxconfig and myapp/.praxrc bash scripts

  • support

  • GNU/Linux:

    • NSSwitch DNS resolver (resolves *.dev domains to

    • firewall rule (redirects root ports 80/443 to user ports 20559/20558)

    • install script


  • Documentation

  • Mac OS X:

    • firewall rule

    • DNS resolver

    • install script

  • Commands for the prax script:

    • prax always_restart

    • prax status

    • prax start –no-restart


  • Julien Portalier <>

  • Sam Stephenson, Nick Quaranto, 37signals for the sub command and Pow!

  • pyromaniac for the initial NSSwitch extension

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