In-service software upgrade in virtual switch stack

The invention relates to an in-service software upgrade in a virtual switch stack. One aspect of the present technology may provide a system for facilitating in-service software upgrade (ISSU) for switches in a virtual switch stack. During operation, the system may initiate an ISSU that facilitates uninterrupted traffic flow. The system may upgrade a first set of daemon processes of the switch, the first set of daemon processes managing operations of the switch. The system may also upgrade a database stored on the switch. The database may store operational information of the switch. The system may also upgrade a second set of daemon processes of the switch, the second set of daemon processes configuring forwarding information about forwarding hardware of the switch, and facilitating data plane operations for the switch. Forwarding information configured on forwarding hardware may remain unchanged during upgrade. The system may configure the upgraded second daemon set to obtain control plane information from a