Correct DNS setup for custom domain with subdomains and CNAMES pointing at them

Question

I have a multi-tenant Rails app, hosted with Heroku at http://myapp.herokuapp.com. The tenants/accounts are separated via subdomains (and Postgresql schemas). I have then added my own domain as custom domain to the Heroku app. Since Heroku really advice against using A records because of "uptime implications" (https://devcenter.heroku.com/articles/avoiding-naked-domains-dns-arecords) I first tried to put a CNAME record from my custom domain to myapp.herokuapp.com. That worked fine also with subdomains like http://clientaccount.mydomain.com.

The problem began when my client wanted her own domain pointing to their account so that http://www.clientdomain.com showed http://clientaccount.mydomain.com, the most obvious solution seemed to be to create a CNAME record in my clients DNS to point to http://clientaccount.mydomain.com. That did not work, when visiting the address an error message stated that "There is no app configured at that hostname", also host www.clientdomain.comgave:

www.clientdomain.com is an alias for clientaccount.mydomain.com
clientaccount.mydomain.com is an alias for myapp.herokuapp.com
myapp.herokuapp.com is an alias for ar.herokuapp.com

After some VERY confused support from Heroku, they advised my to use A records instead pointed to their three apex IPs. So changed it but it still didn't work. They then told me to add my clients domain as a custom domain in my Heroku settings which I have done without good result.

So my current configuration is as follows:

Myapp at Heroku has following custom domains:

*.mydomain.com www.clientdomain.com

mydomain.com DNS

*.mydomain.com has three A records pointing at Heroku apex IPs

clientdomain.com DNS

In the DNS for clientdomain.com, clientdomain.com (without www) is redirected to www.clientdomain.com (Not sure how they do it but it seems to work.)

For www.clientdomain.com there's a CNAME record pointing at clientaccount.mydomain.com

Current state

www.mydomain.com resolves correctly.

clientaccount.mydomain.com resolves correctly.

www.clientdomain.com goes to www.mydomain.com (without subdomain)

So the problem is obvously either in the DNS somehow, does the subdomain fall away somewhere since my application obviously doesn't receive it? Or do I have to change some code in Rails in order to handle this?

The subdomain is handled as route constraint, Subdomain class:

class Subdomain
  def self.matches?(request)
    request.subdomain.present? && Account.find_by_subdomain(request.subdomain)
  end
end

Any input is appreciated!

EDIT

I have done everything that is suggested, do I have to change my application controller as well?

application_controller.rb

def handle_subdomain
  if @account = Account.find_by_subdomain(request.subdomain)
    PgTools.set_search_path @account.id
    @current_account = @account
  else
    @current_account = nil
    PgTools.restore_default_search_path
  end
end

Answer 1

You need to do something like:

def handle_subdomain
  if @account = Account.find_by_subdomain(request.subdomain) || Account.find_by_domain(request.domain)
    PgTools.set_search_path @account.id
    @current_account = @account
  else
    @current_account = nil
    PgTools.restore_default_search_path
  end
end

Notice Account.find_by_domain(request.domain)—although you might need request.host for the full host, not just the domain component.

Answer 2

Your best bet here is to first setup your main domain as follows:

*.mydomain.com as a CNAME to heroku-appname.herokuapp.com

And add *.mydomain.com as a domain name to your app:

$ heroku domains:add *.mydomain.com

Next You'll want to setup an easy way for your users/clients to add their custom domains to your multi-tenant app. This requires two things, adding the domain name to your app and having them setup DNS. Here's the best approach:

add www.myclientdomain.com to your app:

$ heroku domains:add www.myclientdomain.com

Then setup DNS to point into Heroku. You're best off taking a lesson from Heroku's setup and having your clients CNAME to a domain name that you own. This will help avoid lock-in and gives you much more control over where you're directing traffic. so:

CNAME www.myclientdomain.com to proxy.mydomain.com

The CNAME will follow proxy.mydomain.com to heroku-appname.herokuapp.com and then resolve to the Heroku IPs.

Then you should be all set.

Ideally you'll be taking on new customers with custom domains faster than you can add domain names manually so you'll want to automate that step. Using the heroku api and client you can manage your custom domains, programmatically, fron within your app.