Procedure for failover partner replacement.

[Christopher Barry]

On Thu, 11 May 2017 08:35:42 -0500
Bob McDonald <bmcdonaldjr at gmail.com> wrote:

>I've got a failing dhcp failover partner. (the partner is a HA cluster
>and both nodes are being RMAed. Long story)
>
>My question is this. Is the following procedure ok for the replacement?
>(I've already confirmed the new version of DHCP is exactly the same as
>the old one)
>
>1) before shutting down the failing partner cluster, stop DHCP and
>save the dhcpd.leases file and the DHCPD.conf file.
>2) shut down the failing partner cluster completely.
>3) bring up the replacement partner cluster while leaving DHCPD turmed
>off. 4) restore the DHCPD.leases and DHCPD.conf files.
>5) restart DHPCD on the replacement partner cluster.
>
>My contention is that this will result in the failover pair going into
>partner-interrupted state for about 5 or 10 minutes while the HA
>cluster is replaced and then should restart communications as if
>nothing happened when the replacement partner comes live. Thoughts?
>
>Regards,
>
>Bob

What is you DHCP environment like? Short leases and very busy, or
enterprise lease times, separate wireless dhcp? You're probably not an
ISP I'm guessing. You have a cluster for failover, not performance.

I would double the lease time a day or so before, to help deal with
any contingencies that are extremely unlikely to occur. Then stand up
the new cluster or just a spare box while the cluster is getting
replaced, rsync the leases and conf over to the temp or new cluster
primary on a chron for a while without dhcp running there, then, when
the network is quiet, ideally a Friday night, shut down the old
cluster's dhcp and start it on the new one. There would only be seconds
of interruption max if any. dhcp is broadcast and the client really
doesn't care where it's address comes from. Don't make it more
stressful than it needs to be. 


-- 
Regards,
Christopher