1. A method for upgrading at least one hypervisor in a cluster of nodes with a network device that is operative to perform actions, comprising: determining the at least one hypervisor for upgrading, wherein the at least one hypervisor corresponds to at least one virtual traffic manager for a virtual cluster of virtual traffic managers that span at least two nodes; deactivating the operation of the at least one determined hypervisor and the at least one corresponding virtual traffic manager while the virtual cluster remains operative; upgrading the at least one deactivated hypervisor; and re-activating the at least one upgraded hypervisor and each corresponding virtual traffic manager for the virtual cluster.