After setting up a custom domain, visting the associated
.herokudns.com address in my browser shows "There's nothing here, yet."
herokudns.com endpoints are directly browsable, they are only to be used as CNAME targets for DNS. The Heroku routing layer uses the
Host header from the client to ensure the correct application responds to a request - this needs to be set to the value of your custom domain (if you have one set up) to route to the correct application. As a result you cannot access your application by visiting the
herokudns.com address directly.
If you are using Heroku SSL and you want to check the certificate, you can do this using the
openssl command, as described here https://devcenter.heroku.com/articles/ssl#add-certificate-and-intermediaries
For more information using
herokudns.com CNAME targets, please see https://kb.heroku.com/what-is-the-correct-dns-cname-target-for-my-custom-domains.