Service version modification of a high-availability system

In one embodiment, an operating system kernel and/or one or more processes of a high-availability system are modified while the system is operating and providing high-availability service. In accomplishing this, one embodiment uses a second virtual machine to operate a second operating system kernel including a second set of processes in the standby mode, which receive state information from corresponding process(es) in the active mode. Individually, the operating system kernel and processes within the second set of processes may be a same or different version of their counterpart in a first virtual machine and its processes which are being replaced. When the second set of processes have acquired sufficient state information to perform the standby role, the operation of the first virtual machine is typically ceased as the version modified second virtual machine is performing the version modified functionality of the first virtual machine.