CARP issue with 2 Masters
m.seaman at infracaninophile.co.uk
Sun Oct 5 10:11:45 UTC 2008
frank.cam at webprophets.net.au wrote:
> I have CARP running on a master and a slave server and for some unknown reason
> the slave continues to classify itself as a master, even though the advskew is
> higher than on the master.
> It appears that queries sent to the CARP ip address go to the master 50% of the
> time and the slave 50% of the time when both servers are up. This plays havoc
> with my databases as I synchronise them asynchronously.
> When I take the carp interface down on the slave using 'ifconfig carp0 down &&
> ifconfig carp0 up' it lists it's status as 'backup' for about 10 seconds and
> then goes back to 'master'.
Have you by any chance firewalled out the multicast packets that CARP uses
to test for interface death? If either one of a CARP pair can't see CARP packets
frequently enough it will think the other is down and promote itself to master.
If your firewall is blocking, then add a rule like this on both machines:
pass quick on $ext_if proto carp \
from $ext_if:network to $carp_mcast keep state
$carp_mcast is defined as "18.104.22.168"
Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
Kent, CT11 9PW
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