On Thu, 2008-10-23 at 10:48 -0600, Landon Cox wrote:

>     b) apache, postgresql, mysql and some custom services are always  
> running on both machines to reduce startup times on failover

You might want to carefully consider the tradeoff here. Getting two-way
database replication to work reliably can be a huge headache. I have no
experience with postgresql,  but I've never been able to make this work
with mysql. I found it was just easier to use DRBD to replicate the
database at the disk partition level, and put up with the startup time
on failover. Even with a good-size database (that stores several days
worth of e-mail for our 1200-employee organization), it's at most a few
seconds for mysql startup. It was a small price to pay to avoid the
headaches associated with database-level replication. Do you really have
an application where you can't even afford a few seconds down time at
failover?

It is also unclear to me that you can bind an application to an
interface like eth0:0 that doesn't even exist when the application is
started (it is created by heartbeat at failover time). Thus it might not
even be possible to have your apps running before failover and have them
listening on the service address after failover. Has anyone actually
tried this?

--Greg


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