Routing Question by ThirtySharp762 (http://www.reddit.com/r/rubyonrails/comments/28wsoy/routing_question/)

application.html.erb

# ... 

<%= domain_stylesheet_link_tag "application", media: "all" %>
<%= domain_javascript_include_tag "application" %>

#...

application_controller.rb

class ApplicationController < ActionController::Base
  ###... your existing code
  before_action :find_domain
  
  private
  
  def find_domain
    @domain = request.host
  end    
  
end

domain_asset_helper.rb

module DomainAssetHelper
  def domain_image_tag(resource)
    image_tag("#{@domain}/#{resource}")
  end
  
  def domain_image_path(resource)
    image_path("#{@domain}/#{resource}")
  end
  
  def domain_stylesheet_link_tag resource, media: "all"
    stylesheet_link_tag "#{@domain}/#{resource}", media: media
  end

  def domain_javascript_include_tag resource
    javascript_include_tag "#{@domain}/#{resource}"
  end
end

domain_constraint.rb

# This might live in lib/ folder or wherever you want

class DomainConstraint
  def initialize(domain)
    @domains = [domain].flatten
    # you could customize this logic
  end

  def matches?(request)
    @domains.include? request.host
  end
end

index.html.erb

<p> This is my cool page that's shared across domains</p>

<p> I can load images in a few ways using the normal asset pipeline. </p>
<ul>
  <li>
    Using the normal image helpers <%= image_tag("mydomain.com/cool.gif") %>. However this isn't really reusable
  </li>
  <li>
    Using the normal image helpers with my @domain set in application controller <%= image_tag("#{@domain}/cool.gif") %> 
    This will automatically grab the domain and search for it in the assets pipeline.
  </li>
  <li>
    Using a helper method like seen above to clean up these image tags: <%= domain_image_tag("cool.gif") %>. 
    This will automatically grab the domain and keeps your views more pretty.
  </li>  
  
</ul>

routes.rb

MyApp::Application.routes.draw do
  
  # Use a domain_constraint class where you can customize logic for multiple domains, etc.
  constraints DomainConstraint.new('mydomain.com') do
    root to: 'my_domain#index'
    # The rest of your routes for a specific domain could go here
  end

  # Simpler constraint for single domain mapping/routing
  root to: 'your_domain#index', constraints: { domain: "yourdomain.com" }

  # You could set a default route in the event your domain doesn't match the domains you've mapped above
  root to: 'main#index'
end