Redirection to non resolvable hostname

Hello,
I’ve installed Gitlab on Ubuntu 14.04 with the 2 minutes installation doc and when I access the ui http://server_ip, I’m redirected towards http://hostname/users/sign_in
As hostname is not resolvable I cannot accesd this url. I’m sure I missed something but cannot figure out what.
Any ideas ?
Thanks a lot,
Luc