The instruction —
Set DISCOURSE_HOSTNAME to discourse.example.com, this means you want your Discourse available at http://discourse.example.com/. You’ll need to update the DNS A record for this domain with the IP address of your server.
I really think that you should specify it more clearly there.
And i changed discourse.example.com to mydomain.com, not just example.com …
It is working fine now…
Thanks.