Question

I’m trying to setup Subdomains in Rails 3 per Ryan Bates screencast on subdomains. However it’s not working for me. I have the following setup:

# routes.rb
constraints(Subdomain) do
  get 'devices' => 'devices#all'
end

# lib/subdomain.rb
class Subdomain
  def self.matches?(request)
    # binding.pry
    request.subdomain.present? && request.subdomain == "admin"
  end
end

Loading the url admin.localhost:3000/devices should route me to devices#all, however I get a routing error Routing Error No route matches [GET] "/devices" Clearly my routing isn’t working.

I setup a pry debug session where the comment is above, and it gets hit, so my constraint is working, but I get the following output:

[1] pry(Subdomain)> request.subdomain
=> ""
[2] pry(Subdomain)> request.subdomains
=> []
[3] pry(Subdomain)> request.host
=> "admin.localhost"

So rails isn’t picking up the admin portion of the url and placing it into the subdomain variable. While I could easily just use the host value to filter to the admin routes, I’d like to keep things clean and correct.

How come rails isn’t setting the subdomain value?

---

Edit

Both jdoe and coreyward are correct with their answers. What was throwing me off was that I was also using pow and xip.io to access the site and getting the same error. Which was odd because http://admin.app_name.192.168.1.68.xip.io/devices has a tld > 1. What was happening was that the subdomain for xip was admin.app_name.192.168.1.68, which also fails given the matches logic and doesn’t route.

Answer 1

Because there isn’t a subdomain as far as Rails considers it.

Rails expects you to provide a Top-Level Domain (TLD) length for TLDs with more than 1 dot. For example, if you had bbc.co.uk it would pickup “bbc” as the subdomain unless you specified the TLD length is 2, in which case the subdomain would be blank:

request.subdomain(2) #=> ""

This is also why you’re seeing subdomains return an empty array: the last two segments are being discarded automatically. You could specify 0 as the TLD length to get back “admin”, but that code will break in production with a real domain name, so I don’t recommend it.

I recommend using a domain like admin.yourapp.dev that is routed back to your computer via localhost to make your app properly detect a subdomain. Just edit /etc/hosts to do it simply.

If you’re curious, here is the Rails source for the subdomain method.