Method and system for hitless upgrade of chassis in virtualized environment

A first network device that is communicatively coupled to a switch and a virtual router in a network, wherein the switch sends data traffic received from the virtual router to the network, and sends data traffic received from the network to the virtual router, for performing upgrade of route processor virtual machines (RP VMs) and line card virtual machines (LC VMs) located at the virtual router without disruption to the data traffic, the first network device comprising:

• a network interface configured to exchange messages with the network;
• and
• a virtual machine (VM) upgrader, coupled to the network interface, configured to:
• upgrade a second RP VM at the virtual router with a new RP VM image, wherein the second RP VM is serving as a current standby RP VM, and wherein a first RP VM located at the virtual router is serving as a current active RP VM,
• spawn, using a new LC VM image, a second set of one or more LC VMs to serve as current standby LC VMs at the virtual router, wherein each of the one or more LC VMs of the second set of LC VMs corresponds to an upgraded version of a LC VM of a first set of one or more LC VMs serving as current active LC VMs at the virtual router,
• perform incubation of standby virtual machines (VMs) at the virtual router, by configuring the switch to forward data traffic to both the first and second set of one or more LC VMs, thereby allowing system states of the standby VMs to be auto-populated by the data traffic, and
• after the incubation has completed, swap roles between current standby RP/LC VMs and current active RP/LC VMs at the virtual router, such that data traffic are exchanged only between the switch and the upgraded VMs at the virtual router.