[Samba] Upgrade Ubuntu 20.04 4.16.11 to current

[Greg Sloop <gregs@sloop.net>]

I've got a few DC controllers.
I believe two are on Ubuntu 20.04, and running 4.16.11.

I'm finally getting time to roll these up to something newer.

Thus, I'm kind of casting about for the "best" way to "upgrade" these.

Some details.
All of these are VM's running under XCP-NG - so grabbing a snapshot and
rolling back is trivial, if the upgrade goes awry. (At least as long as the
DC hasn't made changes to the AD database.)

So, as I see it, there are two ways of going about it.

Option 1) Upgrade ubuntu from 20.04 to 22.04->24.04 (It has been around a
couple of months now for 24.04, so I'd expect it to be pretty stable and an
upgrade should go well enough.)
Then update the samba packages - I'd probably continue to rely on MJT's
repos - and go to 4.20.1.

Option 2) Build completely new VM's on 24.04 and install MJT's repos and
join them to the domain and then demote and remove all references to the
old controllers.

(Unless there's some really compelling reason for the second option, I
think I'd prefer the first.)

Questions about specific components.
Any thoughts on using Ubuntu 24.04?
Is 4.20.1 stable enough, or should I plan on going to 4.19.7?

---
If I upgrade them in-place, I assume the "best" method would be to stop
samba and disable from starting at boot.
Then run the Ubuntu upgrades.
Once those are done, install the desired MJT repo (4.19 or 4.20) and intall
the desired version.
Then start the AD packages.
(I'd probably do the non FSMO controller first, and see how it goes. If it
goes well and seems stable I'd try to do the FSMO master next.)

What testing should I be doing at that point to verify that everything is
ok?

Is there a good way of making a solid backup of the AD db, should I need to
roll back to it? (Separate from the VM snapshots and backups I already
have.)

Glad for any pointers!

-Greg