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[Samba] IP aliases of DCs to prevent DNS timeouts

Hi All,

In my environment, I have a total of 4 DCs (Samba 4.7.6) running in VMs. Their uptime schedule goes like this:
dc00 : usually 100% unless there's a failure.
dc01 : same as above
dc02 : a few days per week.
dc03 : a few days per month.

This has the consequence that a DNS A lookup on the AD domain shows 4 IPs, 2 of which are usually not up.

Because I don't have shared storage in this setup and since all of the VM's hosting the DC's are orchestrated externally, I decided to come up with the following sequence:

- When any of dc01, dc02 or dc03 goes down, relocate its IP on dc00 so that the IP address answers DNS on behalf of the dc that's down. - When the VM comes back up, remove the IP alias from dc00 and let the VM grab it.

On a normal given day, when dc02 and dc03 are both down, this is what it looks like on dc00:

# ip -4 -o a|cut -c-60
1: lo    inet scope host lo\       valid_lft for
4: bond0    inet brd scope glob	# < dc00's main IP.
4: bond0 inet scope global secondary bond # < dc02's main IP. 4: bond0 inet scope global secondary bond # < dc03's main IP.

While this appears to work fine and solves the DNS issue of hanging on DNS requests, I'm wondering if this might be causing problems in the future or induce issues that I wouldn't be having if I only had two DC's instead. I think DRS replication would probably be impacted but since it negociates a p-to-p channel with its peer(s) I don't think it would cause corruption.

Also, one thing to note is that this forced me to move from the SAMBA_INTERNAL DNS backend to BIND9_DLZ so that bind would be able to answer DNS queries on IP aliases. (otherwise nslookup complained that I asked but it was a different IP that answered).

Any guidance welcomed. :)


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