My gitlab works in internal network, but fail to get access from external

I am very new to Linux so please accept my apology if I have asked some stupid questions. I have just setup an ubuntu server 14.04 on a VM and installed gitlab omnibus onto it. I can see the page of gitlab when I enter the IP of my VM into my browser.

I want to let my friend access my gitlab, so I did the following things:

• I applied a domain name in noip.com and installed the application from noip.com which keeps my IP updated to their server.
• I configured my router to forward port 80 to my VM
• I edited /etc/gitlab/gitlab.rb and put external_url 'http://my-domain-from-noip.noip.me'. Then gitlab-ctl reconfigure and gitlab-ctl restart

However, I still cannot see my gitlab with http://my-domain-from-noip.noip.me I have pinged the domain and port and it is responsive, so I guess the domain redirection and port forwarding are working.

May I ask what I should do next to make my gitlab be accessible by my friend?

Thanks in advance