All non-primary slots have been rebooted so the primary slot is the only one left to reboot. To reboot the primary slot, a failover will be performed resulting in the current primary slot being rebooted and thus completing the last step of the rolling upgrade process. Unless there is a failure, this will be the last event generated from the rolling reboot.
No action required - Informational message only.
Warning
All non-primary slots have been rebooted. To finish the rolling reboot process, a failover will be performed.