A Stack Rolling Software Upgrade (Rolling Upgrade) enables a stack to continue functioning during a software upgrade. The benefit of a Rolling Upgrade is minimal impact to the devices connected via a LAG or other multi-homing technologies that allow a device to be simultaneously connected to different stack nodes. Performing a Rolling Upgrade does not change the current method of installing software, only how the stack is rebooted.
The Rolling Upgrade process reboots all the Standby nodes, reboots the Backup node, and then initiates a failover to make the old Backup node the new Primary. The failover results in the old Primary node rebooting. Since the selected software version on each node is the newer, upgraded software version, after each node reboots, they will run the new software version.
Performing a Rolling Upgrade contains steps on initiating a Rolling Upgrade.