cname lookup

application.rb

class ApplicationController < ActionController::Base
  before_filter :load_site

private
  def load_site
    if request.host =~ Site.domain_pattern
      subdomain = current_subdomain
    else
      subdomain = find_cname(request.host)
    end
    
    @site ||= Site.find_by_subdomain(subdomain)
    
    render :text => 'Site not found' unless @site    
  end
  
  def find_cname(host)
    Rails.cache.fetch("dns_map:#{host}") {
      Net::DNS::Resolver.new.query(host).each_cname do |cname| 
        return $1 if cname.match Site.domain_pattern
      end
    }
  end
end