Geoffrey Young wrote: > we do that frequently here - 7 servers behind a BigIP. I've always > wondered, though, whether this approach is foolproof for major > upgrades for applications that maintain state - since a user might > have a session created using a new-code box, then hit an old-code box > on the next page view. it takes us many minutes to work through > restarting the entire array. > > were you ever concerned about something like that?
We also used BigIP, with the sticky load-balancing option on. (Well, we used two, and only the application servers were sticky. It didn't matter which proxy/web server you went to.) This prevents the problem you're talking about. Of course if the upgrade involves changing some shared resource like a database as well, you have to take the site off-line while you do it. I suppose it's possible to rig up something crazy with multiple databases and synchronization, but it's just not worth it. - Perrin
