Mongrel: Simple Fast Mostly Ruby Web Server

Mongrel is a small library that provides a very fast HTTP 1.1 server for Ruby web applications. It is not particular to any framework, and is intended to be just enough to get a web application running behind a more complete and robust web server.

What makes Mongrel so fast is the careful use of a C extension to provide fast HTTP 1.1 protocol parsing and fast URI lookup. This combination makes the server scream without too many portability issues.


The 0.3.6 release supports Ruby On Rails much better than previously, and also sports the beginning of a command and plugin infrastructure. There is now a more complete CGIWrapper that handles most of the CGI usage, but still doesn't do the MIME decoding or file upload/send (it leaves that to CGI). Finally, there's a great mongrel_rails_service script for running under Win32 as a service.

After you've installed (either with gem install mongrel or via source) you should have the mongrel_rails command available in your PATH. Then you just do the following:

> cd myrailsapp
> mongrel_rails start

This will start it in the foreground so you can play with it. It runs your application in production mode. To get help do:

> mongrel_rails start -h

Finally, you can then start in background mode (probably won't work in win32):

> mongrel_rails start -d

And you can stop it whenever you like with:

> mongrel_rails stop

All of which should be done from your application's directory. It writes the PID of the process you ran into log/

There are also many more new options for configuring the rails runner including changing to a different directory, adding more MIME types, and setting processor threads and timeouts.

Win32 Service Support

Mongrel now has support for running as a Win32 service right out of the box. The support is still rough but works well enough that we decided to release it. You can thank Luis Lavena for working on this and making it so nice.

After you do the gem install, find a Rails application you want to run and do:

$ mongrel_rails_service install -n myapp \ 
    -r c:\my\path\to\myapp -p 4000 -e production
$ mongrel_rails_service start -n myapp

Now hit the port and poof, works. *Stopping the service is a little problematic right now.*

If you run into an app that's not running right, my suggestion is to run it with the regular mongrel_rails runner:

$ cd c:\my\path\to\myapp
$ mongrel_rails start -p 4500

Since that will spit out error messages and stuff to the console. *Use CTRL-Pause/Break to stop.*


It doesn't explicitly require Camping, but if you want to run the examples/camping/ examples then you'll need to install Camping 1.2 at least (and redcloth I think).

These are all available from RubyGems.

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.

Finally, the source includes a setup.rb for those who hate RubyGems.


The examples/simpletest.rb file has the following code as the simplest example:

require 'mongrel'

class SimpleHandler < Mongrel::HttpHandler
   def process(request, response)
     response.start(200) do |head,out|
       head["Content-Type"] = "text/plain"

h ="", "3000")

If you run this and access port 3000 with a browser it will say “hello!”. If you access it with any url other than “/test” it will give a simple 404. Check out the Mongrel::Error404Handler for a basic way to give a more complex 404 message.

This also shows the DirHandler with directory listings. This is still rough but it should work for basic hosting. *File extension to mime type mapping is missing though.*


Like previous releases 0.3.1 continues the trend of making things as fast as possible. It currently might be a little slower than other releases but should hold up pretty good against at least WEBrick (especially when running Rails).

As before you can control the number of processor threads (and thus ActiveRecord database connections) with:

h ="", "3000", 40)

Which will make 40 thread processors. Right now the optimal setting is up in the air, but 20 seemed to be about the sweet spot on my systems. The limited processors also means that you can use ActiveRecord as-is and it will create a matching database connection for each processor thread. More on this in future releases.

The Future

With the core of Mongrel completed I'm now turning to the next set of features to make Mongrel useful for hosting web applications in a heavily utilized production environment. Right now I'm looking at:

  • An idea I've had for an insane caching handler which could speed up quite a

few deployments.

Overall though the goal of Mongrel is to be just enough HTTP to serve a Ruby web application that sits behind a more complete web server. Everything in the next will focus on actually hosting the major web frameworks for Ruby:

  • Camping – because it's already done (thanks Why).

  • Ruby on Rails – that's where my bread is buttered right now.

  • Nitro – Nitro folks have already hooked this up and started using it. Nice.

  • ????? – Others people might be interested in.


E-mail zedshaw at and I'll help. Comments about the API are welcome.