SubdomainFu provides a modern implementation of subdomain handling in Rails. It takes aspects from account_location, request_routing, and other snippets found around the web and combines them to provide a single, simple solution for subdomain-based route and url management.


SubdomainFu is available both as a traditional plugin and a GemPlugin. To install it as a traditional plugin (Rails 2.1 or later):

script/plugin install git://

To use it as a gem, add it to your config/environment.rb:

config.gem 'subdomain-fu'


SubdomainFu works inside of Rails's URL Writing mechanisms to provide an easy and seamless way to link and otherwise understand cross-subdomain routing. You can use the :subdomain option both in named and non-named routes as well as in generated resources routes.

Let's say my domain is ''. Here are some examples of the use of the :subdomain option:

url_for(:controller => "my_controller", 
        :action => "my_action", 
        :subdomain => "awesome") # =>

Now let's say I'm at and I want back to the root. Specifying “false” will remove any current subdomain:

users_url(:subdomain => false)  # =>

Note that this plugin does not honor the :only_path notion of routing when doing so would go against the intent of the command. For example, if I were at again:

users_path(:subdomain => "fun") # =>
users_path(:subdomain => false) # => /users

In this way you can rest assured that you will never misdirect your links to the same subdomain when you meant to change it.

Use in controllers and views

You have access to current_subdomain and current_domain methods.


returns all subdomains. For the URL, it will return “”


returns all subdomains except for the subdomain, including the TLD. For the URL, it will return “”

If what you really want is the entire domain, then use request.domain in your controllers. The purpose of current_domain is to only strip off the first subdomain, if any, and return what's left.


You may need to configure SubdomainFu based on your development setup. The configuration required is:

TLD Size

A hash for each environment of the size of the top-level domain name. ( = 1, localhost = 0, etc.)

SubdomainFu.tld_size = 1 # sets for current environment
SubdomainFu.tld_sizes = {:development => 0,
                         :test => 0,
                         :production => 1} # set all at once (also the defaults)


Mirrors are the subdomains that are equivalent to no subdomain (i.e. they 'mirror') the usage of the root domain.

SubdomainFu.mirrors = %w(www site we) # Defaults to %w(www)

Preferred Mirror

SubdomainFu also understands the notion of a 'preferred mirror', that is, if you always want your links going to '' instead of '', you can set the preferred mirror like so:

SubdomainFu.preferred_mirror = "www"

Now when you create a link with :subdomain => false in the options the subdomain will default to the preferred mirror.


SubdomainFu can also work within Rails' routing for subdomain-specific routes. For instance, if you only wanted your administrative tools available in the “admin” subdomain you could add this to your config/routes.rb file:

map.with_options :conditions => {:subdomain => 'admin'} do |admin|
  admin.resources :posts
  admin.resources :users

In addition to specifying a string, you could also specify false to require no subdomain (this includes mirrors that you've set up such as www) or a regular expression to match a range of subdomains.


Copyright © 2008 Michael Bleigh ( and Intridea, Inc. ( Released under the MIT license