[Samba] Active Directory Administrative Center cannot connect to an domain despite Workstation successfully joined the domain

[samba-th at pfoertner-net.de]

Hello,

I am trying to set up a new domain using Samba for the DC.

I followed two concepts, one was to use an existing docker container for
that purpose (samba 4.3 on ubuntu 18.3), the other was to set it up
myself on a plain ubuntu image (Ubuntu 18.04.3 LTS, samba 4.7.6).

Thanks to the pretty good samba wiki I got the a promising point with
these things working well:
 * DC up and running
 * all checks found in the wiki and elsewhere passed, especially about dns
 * newly installed PC joined the domain (latest Windows 10, 19.10)
 * login on the PC as domain administrator or any other domain user
 * RSAT tools activated via optional features
 * setting up new groups and users using "Active Directory Users and
Computers" from the windows PC
 * "Group Policy Management" seems to work, but I did not really do
something here yet.
 * same for "Active Directory Sites and Services"
 * "DNS Manager" seems to work, however the forwarder that has been set
up and is definitely working, is not listed

so far so good. Now I wanted to add a share to the server (target is to
enable roaming profiles but this is not relevant yet). Preparations on
the server editing smb.conf are done and the rest should be done from
windows according to the wiki. And here start the problems:
 * starting "Active Directory Administrative Center" gave a warning that
it "Cannot connect to any domain" despite the machine is in the domain
and I have logged in as the domain administrator

What also puzzles me is that AD Module for Windows Power Shell starts
with a warning 'Unable to find a default server with Active Directory
Web Services running'. Some newer RSAT tools, like the "Administrative
Center" seem to be browser based. All others work find. But I did not
find AD Web Services mentioned anywhere in relation to samba.
Where is the problem or missing link? What can I do find out more or get
closer to a solution?

regards
Thomas