HA (High Availability)

Tools like VMWare HA can, in case of a server failure, re-start virtual machines, automatically on another server. The tools also monitor the capacity of a server and choose an optimal server for the VM to run. In case of failure of the underlying physical resource, the machine is restarted, not dynamically moved, which means that there will be service downtime. This can be prevented by clustering firewalls even in virtualized network.

the requirement that a business service be continuously operational for a desirably long length of time.

A combination of technology, processes, and support partnerships that provide greater application or system availability.