OS X Server behind an ADSL router I have a Mac Mini with OS X Server installed on my LAN that I use as a Git server and Continuous Integration server. I would like to be able to use these services from outside my LAN but I'm not sure what to do to make it work.

My network goes all through an ADSL router and its IP is not static. From what I've read so far I need a DDNS service to provide me a static address to my server. I subscribed to one and configured a their client on my server to hourly update the IP. 

Now I have a host address that I don't know what to do with it, it does not provide me any of the services my server provides when I try to access it… Do I have to open some ports?
I've been doing exactly what you describe for 8 years, it works just fine.

I assume you set up Server with your internal IP address, and that it is a fixed IP on the local network? Server does NOT like having it's IP address changed.

The external address can change 10 times a day. You say you already have a domain and a dynamic update service - I assume it's one that updates your domain A record when your external address changes? All good.

Yes, you will have to forward a ton of ports. This is another reason you need a fixed ip address on your LAN. Either forward the ports you need or just DMZ the server ( expose it to the internet ) but mind that the router does not also assign the server the global IP address.

To get an idea of which ports are needed for each service, take a look at TCP and UDP ports used by apple products.