US Patent 9507586 Virtual machine based controller and upgrade mechanism

High availability for a network may be achieved, for example, during a hitless upgrade by creating a replica controller virtual machine of an operating controller virtual machine (source controller). The replica controller virtual machine may be on a same or different server as the source controller virtual machine. The replica controller virtual machine may be copied with processes present in the source controller virtual machine and synchronized for runtime state. Upgrades or changes to software applications run in the source controller virtual machine may be provided to the replica controller virtual machine. Once enabled, the replica controller virtual machine may be operated without suspension of the source controller virtual machine.