Hi Tobias,
'IP address of QLUSTAR_MAIN_HEADNODE is not defined in nameservice (NIS)' is indeed the critical error. I haven't seen this error for a long time and the error text is a bit outdated since we added support for dnsmasq, which should now define the IP address of the QLUSTAR_MAIN_HEADNODE, aka. beosrv-c.
So that has to be tested. Log in to the server and try running
ping beosrv-c
This should resolve to the IP of the server and ping sucesfully. But I expect not in your case.
If that fails then check that dnsmasq is running with:
systemctl status dnsmasq
Also beosrv-c must be one of the hosts listed in /etc/dnsmasq.conf.
As for the hostname for cl-login. In qluman a host can have multiple names. For qluman the primary name is the Cluster node name, which is also used to generate names for different networks the host may be on. The rules for generating those names are defined in the network config. A host can also have aliases associated with each network and the visible hostname can be changed. Once you have a cert and the GUI running select cl-login in the Enclosure View. At the right the information for the host then shows up. At the top where it says "Override hostname" you can change the visible hostname for the node to match the external name.
Best,
Goswin