As this is a season of R80 Upgrade, just sharing my experience of recent upgrades in the live environment from R77.30 to R80.20 without any service down
1.Upgrade the DA Agent to the latest version
2.Upload the R80.20 Image through CPUSE and verify for any errors
3. In CMA cluster Properties, Select Maintain current cluster Active member
4.Upgrade on the current standby FW(CPUSE) and let it Reboot
5. Once rebooted, Change the Gateway Object to R80.20 version(It will change for all 3 objects)
6.Install policy(Uncheck the option- For gateway clusters, if installation on a cluster member fails, do not install on that cluster)
7. Check the HA in new version FW,(HA module will be Ready)
8. Now do the upgrade in another gateway, During a reboot, the other pair on HA-Ready will become Active
9.No service Interruption and the other FW will take HA Active(Few Packet Drops-2 to 3 RTO)
Now verify both status and do a final Policy Installation by "Keep Check" the actions
10. Now Install the Hotfix.R80.20 Jumbo Hotfix Accumulator General Availability(Take 87)