Sorry for being unclear previously.
We have a vmware virtualized server instance that is our main production server. I stores a series of web based applications on close to a hundred unique top level domains. For serving web pages we use a LAMP stack. This server is running our primary and secondary dns servers (on two different ip address than that used for serving web content). And finally we also host our mail (pop and smtp) using exim (i believe).
Recently we've had issues causing our root fs to become read only, preventing apache2 or mysql connections and prevent incoming email. Essentially taking down the web presence and email for many thousands of clients. The nature of the issue (still undetermined by under control) did not affect the bind so dns was still resolving fine.
Since then, we have begun to mirror the production web sites and associated mysql databases onto a secondary server. This server is completely production ready.
My question is, what are recommended methods for a failover in the case that apache on our main production server fails (for what ever reason) to quickly, if not automatically, start forwarding traffic as seamlessly as possible to the secondary.
DNS round robining is undesirable for us since we do not wish to the load over two servers, in fact we only ever want the secondary to receive http requests in the case the main server is non-responsive. This is in part to the fact that our mirroring process is one way and changes to the secondary server would be reflected in the main server and even lost.