how to upgrade the failover pair?

[Aleksey Perov]

Hi.

I have two servers running Debian 6.0.5 with ISC DHCP 4.1.1 in a 
failover pair. Now I need to upgrade them to the latest Debian 9 which 
is shipped with ISC DHCP 4.3.5. Since Debian 6 is too old, the only way 
of upgrading is a clean reinstall (which in most cases is better than 
sequential upgrade 6 to 7 to 8 to 9).

I have read 
https://kb.isc.org/article/AA-01043/183/Recommendations-for-restarting-a-DHCP-failover-pair.html 
and some other articles, but those documents say nothing about the 
upgrade scenario.

So the question is: What is the recommended process of _upgrading_ the 
failover pair?

The draft plan is as follows:

- stop the secondary;
- turn the primary into partner-down;
- reinstall the secondary;
- wait until the primary reclaims all addresses in all pools;
- stop the primary;
- copy leases file from primary to secondary;
- start the secondary in partner-down mode;
- reinstall the primary;
- turn the secondary into normal mode;
- start the primary.

Is anything wrong here?

Any advices and recommendations are welcome. Thanks.




-- 
Aleksey