Why can't I access `herokudns.com` CNAME endpoints in my browser?


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.