Recovery protocol - minimize outage time

[Amanda Edades]

Hello,

I'm planning to migrate from a single DHCP server, to two servers with a
load-balanced configuration.  We serve a number of large networks, and I am
trying to think of ways we can minimize total outage time and the duration
of the recovery process given the number of leases we have to manage.

My understanding of the way the servers would work using the
load-balancing/failover protocol built into the dhcpd process (questions
follow):

·

[image: Inline image 1]


Questions:


What are max-response-delay and mclt times others have used in production
with success in times of a failure?


Is there a way to "override" the lease database transfer to speed it up or
has anyone attempted to do so?  (e.g. override the database transfer and
perform this manually in a faster way, then manually signal both servers
that the transfer is done)

I plan to set mclt time to 60 seconds, making the secondary server issue
leases of 60 seconds, but also minimizing the waiting period during which
no servers will respond to requests to 60 seconds.  I estimate the time to
transfer the lease database will be *at least 16 minutes *for the number of
leases we have - about 350,000.  (I observed about 22,000 leases
transferred per minute observed in lab for empty/free leases.)  In the
worst case, I am not sure if a single server can handle potentially up to
350,000 leases being renewed every 60 seconds for 16+ minutes... I plan to
test this also, but would like to understand how the lease database is
transferred to try to save time there.


Thank you
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