According to this Heroku documentation we can allow a Heroku app hosted at myapp.herokuapp.com to be accessed with a custom domain myapp.com.
I have added the follow records to my GoDaddy DNS Zone File:
A (Host)
Host Points To TTL
--------------------------------------------------
@ 50.63.202.1 1/2 Hour
CName (Alias)
Host Points To TTL
--------------------------------------------------
email email.secureserver.net 1/2 Hour
ftp @ 1/2 Hour
www myapp.herokuapp.com 1/2 Hour
Normally the A record points to a server. In this case Heroku doesn't provide an IP address for its cloud applications, and apparently CNAME is enough.
Navigating to www.myapp.com or myapp.com redirects to https://myapp.herokuapp.com. However, navigating to http://www.myapp.com/blog/post/1 (any address not the homepage) will stay with the www.myapp.com domain, and clicking links is OK -- Except when clicking a link to the homepage we are redirected to the myapp.herokuapp.com address.
How can it be set up so the visitor does not see the herokuapp.com address unless visiting it with that address?
The output of heroku logs --tail --app myapp:
2016-03-11T01:13:49.756887+00:00 heroku[router]: at=info method=GET path="/" host=vast-hamlet-33090.herokuapp.com request_id=6177aa6c-dc5f-4de5-a1c6-1ff8b1194849 fwd="24.17.117.236" dyno=web.1 connect=1ms service=24ms status=304 bytes=181
2016-03-11T01:13:49.760014+00:00 app[web.1]: 24.17.117.236 - - [11/Mar/2016:01:13:49 +0000] "GET / HTTP/1.1" 304 - "-" "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36"
It looks like the app never receives a request from www.myapp.com, but only myapp.herokuapp.com.
The output of heroku domains -a myapp:
=== myapp Heroku Domain
myapp.herokuapp.com
=== myapp Custom Domains
Domain Name DNS Target
------------------ -------------------
www.myapp.com myapp.herokuapp.com
myapp.com myapp.herokuapp.com