I'm interested in finding out the scalability of this forum software, How does it scale across multiple machines?
I'm not really concerneed with DB backend (mysql clusters are rather easy to setup), But with Vanilla on the frontend. Can they share 1 DB backend? How does Vanilla handle sessions, If you go from Machine 1, and are bounced over to machine 8 cause of the Loadbalancer will it gracefully pick up and carry on, or will Vanilla prompt the user with a login box, or a permision denied to post (cause you were in the middle of a post when you bounced for example).
I use Vanilla hosted on the main university server where I study, which consists of god knows how many servers. It generally doesn't like sessions. When using the Wordpress admin interface for example it asks you to login constantly between pages if the load balancer decides that your request is going to be issued from a different server in the cluster.
Luckily they offer a subdomain, www-same.dur.ac.uk which provides a single server from the cluster which therefore ensures sessions are carried across from page to page, which solves any session problems. I'm assuming Vanilla will have the same issues as Wordpress. I notice that if I'm logged in on www-same. domain, then visit the www. domain then I'm logged out.
This is all using the same single mySQL server, although there is probably some sort of clever mirroring system in place to ensure they have backups. It used to be the case that the DB server was taken down for 10-15 minutes each day for backup, although much more of the entire university website relies upon the mySQL server, so it wasn't really practical to do so any more.
It possibly also depends upon your load balancer/cluster configuration, although I don't know much about that. I'm sure there must be a way to carry sessions across multiple machines in such a situation.