We wish to host multiple apps across multiple servers. What we are looking for (ideally) is an existing solution which will work. For example, normally to do it we'd follow a route (for failover) like:

• App is installed on one server along with mysql database
• App is also installed on a second server. Rsync is used to mirror the files over to the second server and ensure consistency
• MySQL is installed with a Master->Slave setup.
• We use a service such as DNS Made Easy which has a DNS failover. If one server goes down it automatically routes traffic to the backup server

We have done the above a few times and generally its fine. The issue I have here is that the above is for one app. What I would like to look at is how we can manage for multiple apps and if there is a layer (such as VMWare) that has complete mirroring built in at the OS level? For example how do web hosts currently do it when they ensure that more than one machine is running a bunch of hosted websites. If you were running hosting and you had 200 clients on a server you would want the same clients across 2 or more servers and want everything mirrored.

Any advice would be much appreciated.