Custom Subdomains in Rails 3

Rails 3 supports subdomains out of the box, which is great. But did you know that the constraints in the Router can actually match patterns too? This means instead of hardcoding each subdomain into your routes you can allow your customers to decide their own subdomains.
However, we have to be careful with pattern matching on the subdomain. There are obvious subdomains we don’t want to match. Like ‘www’, ”, nil, and others that we may reserve. In this case using a pattern match might not be best.

http://bcardarella.com/post/716951242/custom-subdomains-in-rails-3