SubdomainFu: A New Way To Tame The Subdomain

An extremely common practice for Rails applications is to provide keyed
access through subdomains (i.e. However,
there has never been a real unified convention for handling this functionality.
DHH’s Account Location
works for some circumstances but is more tailored for a Basecamp domain model
(i.e. the app is on a separate domain from all other functionality, so you
can always expect a subdomain) than the more common usage of one domain only.

SubdomainFu aims to provide a simple, generic toolset for dealing with subdomains
in Rails applications. Rather than tie the functionality to something specific
like an account, SubdomainFu simply provides a foundation upon which any
subdomain-keyed system can easily be built.

Usage Fu

SubdomainFu works by riding on top of the URL Rewriting engine provided with
Rails. This way you can use it anywhere you normally generate URLs: through
url_for, in named routes, and in resources-based routes. There’s a small
amount of configuration that is needed to get you running (though the defaults
should work for most).

To set it up, you can modify any of these settings (the defaults are shown):

Now when you’re in your application, you will have access to two useful
features: a current_subdomain method and the URL Rewriting helpers.
The current_subdomain method will give you the current subdomain or
return nil if there is no subdomain or the current subdomain is a mirror:

The URL rewriting features of SubdomainFu come through a :subdomain option
passed to any URL generating method. Here are some examples (in these examples,
the current page is considered to be ‘’):

While this is just a simple set of tools, it can allow the easy creation
of powerful subdomain-using tools. Note that the easiest way to locally
test multiple subdomains on your app is to edit /etc/hosts and add
subdomains like so:

Adding an entry for each subdomain you want to use locally. Then you need
to flush your local DNS cache to make sure your changes are picked up:


SubdomainFu is available both as a traditional plugin and as a GemPlugin
for Rails 2.1 and later. For a traditional plugin, install like so:

For a GemPlugin, add this dependency to your environment.rb:

Implementing A Simple Account Key System

Let’s take this functionality and implement a simple account-key system based
off of the subdomain. We’ll start with some controller code (assuming that
we have an Account model with a ‘subdomain’ field):

That’s really all we need for a basic setup, now let’s say we have a
ProjectsController that you must specify an account to access:

There’s lots more you can do with the plugin, but this is a simple use case
that everyone can relate to.

Resources and Plans

A feature that I hoped would make it to the first release of SubdomainFu
but is now a planned feature is subdomain-aware routing so that you can
add conditional subdomain routes to your routes.rb file. Keep an eye
out for more on that in the future.

In the meantime, the project will live at its home on Acts As Community for intermittent
updates, is available on GitHub as always, and bugs/feature requests may
be passed on through the Lighthouse.