Hosting multiple domains from a single Rails app

January 21, 2009

January 21, 2009

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Not long ago, we decided to create an additional domain for a new tool on our website. This tool was sufficiently unique that we wanted to give it its own identity… while still tying it into the branding. Obviously, we could have just created a new Rails app and coded up a website with links back to TransFS… but why do all that extra work? We wanted a way to host this new domain directly from our existing rails app.
Some of our reasons for doing this:
  • Simplify the backend: server maintenance, releases, and hosting costs
  • Repurpose existing CSS, images, javascript, etc
  • Repurpose existing code (avoid complications of git submodules keeping shared code in sync between separate Rails apps)
However, we quickly realized that Rail’s doesn’t really support hosting a separate domain from the same app… at least, not out of the box. What we needed was the ability to use routing rules to specify that requests coming from our new domain,, be directed to specific a Controller. Fortunately, we came across a couple of extremely useful blog posts that helped solve this problem for us. First, Jamis Buck gives this excellent clinic on the guts of Rails routing: Under the hood: route recognition in Rails The most helpful resource for us was this: Rails routing based on hostnameWe were able to adapt the code used in the above link for our purposes… allowing us to create custom routes that were conditioned on the domain name. Here’s what ended up in one of our initializers:
# This allows us to set up custom routes that depend on the domain or host of the request, ie:
# map.connect '', :controller => 'blah', :action => 'blah', :conditions => {:domain => 'blah'}
module ActionController
  module Routing
    class RouteSet
      def extract_request_environment(request)
        env = { :method => request.method }
        env[:domain] = request.domain if request.domain
        env[:host] = if          
    class Route
      alias_method :old_recognition_conditions, :recognition_conditions
      def recognition_conditions
        result = old_recognition_conditions
        result << "conditions[:domain] === env[:domain]" if conditions[:domain]
        result << "conditions[:host] === env[:host]" if conditions[:host]        
Then, we could use this in our routes.rb in the following way:
  map.connect '', :controller => 'true_cost_calculator', :action => 'new', :conditions=>{ :domain=>'' }
Thus… when someone visits, they are directed to our TrueCostCalculatorController!We loved this solution. It saved us a ton of time and effort, and kept our codebase nice and clean.

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