[Samba] Error joining Samba 4.7.4 DC to existing Win2008R2 domain

[Claudio Nicora]

> And I can now confirm that 4.7.4 on the latest Ubuntu 18.04 snapshot
> joins to a Samba AD domain as a DC.
I'm sure it does, that's why I suspect something is wrong in my 
Win2000-->Win2008R2 upgraded domain AD.

> Another thing that comes to my mind is that the 2008R2 domain was 
> upgraded from an initial Win2000.
> Win2000-->Samba direct migration is not possible because Samba
> requires at least a Win2003 domain.
> So the complete upgrade was Win2000 (SRVAD-OLDOLD) --> Win2008R2 
> (SRVAD-OLD) --> Domain/forest functional level upgrade --> Samba
> 4.7.4 migration.
>
> Could there be something wrong/unexpected in current Win2008R2 domain 
> config?

Could you suggest something to check for?
Even with -d9 there's nothing interesting between the last "Adding DNS..." line and "Join failed - cleaning up".
There should be an explanation of why the join failed, other than "It failes, I'm cleaning up".

> As a side note, it took me longer to give the Ubuntu VM a fixed ip etc
> than it took to join as a DC and then people ask me why I don't like a
> certain set of packages ;-)
I agree.
Netplan is not something I was needing; another (needless) thing to 
learn and yet another configuration format to know (even if I love YAML 
for other things).

Claudio