“The idea of using virtual machines to build high available
clusters is not new. Some software companies claim that
virtualization is the answer to your HA problems, off course that’s
not true. Yes, you can reduce downtime by migrating virtual
machines to another physical machine for maintenance purposes or
when you think hardware is about to fail, but if an application
crashes you still need to make sure another application instance
takes over the service. And by the time your hardware fails, it’s
usually already too late to initiate the migration.“So, for each and every application you still need to look at
whether you want to have it constantly available, if you can afford
the application to be down for some time, or if your users won’t
mind having to relogin when one server fails…”