[CentOS] squid HA failover?

[J Potter]

Assuming server A with IP M, server B with IP N, and DNS entry X  
currently pointing at IP M:

1) Add heartbeat on servers A and B, with heartbeat managing a new IP  
address O (this is your virtual IP -- nothing to do with VRRP, that's  
for your routers to failover your gateway).
2) If you want active-active load sharing on servers A and B, install  
pound on both server A and B, and in your pound config, point pound to  
IP M and IP N (same pound config on both servers),
3) Update your DNS to point entry X to IP M.

If you want active-standby on your squids, then have both squids bind  
to 0.0.0.0 and you're done. The standby server will have squid  
listening to requests, but since standby won't have the VIP O, it'll  
just sit there. In this setup, heartbeat is only managing the VIP, but  
no services.

If you want active-active on your squids, then have squid on server A  
bind to only IP M, squid on server B bind to only IP N, and pound  
configured to bind to only IP O. Heartbeat will need to be configured  
to start pound on failover (since IP O will only exist on one box at a  
time, so pound can't bind to it unless the interface is up).

Make sure you test the case where squid (or pound in active-active) on  
the server running VIP O crashes.

-Jeff