The firstboot inithook should give you the option to join an existing domain (not just create a new one). Have you tried that and it's not working? If so, please let me know and I'll have a look and see if I can reproduce the issue.
Or did you just miss that option? If you just missed it, you can interactively re-run the Samba/DC component on the firstboot scripts like this:
The firstboot inithooks should allow you to join a domain
The firstboot inithook should give you the option to join an existing domain (not just create a new one). Have you tried that and it's not working? If so, please let me know and I'll have a look and see if I can reproduce the issue.
Or did you just miss that option? If you just missed it, you can interactively re-run the Samba/DC component on the firstboot scripts like this:
Regardless, the relevant Samba doc page (specifics for joining an AD Domain) should allow you to manually do that if you wish.