In order to upgrade all nodes in a clustered environment, one will need to temporarily break the cluster. This should be done during a maintenance window as this will cause down time.
Below is an example process of Active/Passive PPS Cluster running the impacted PPS versions 5.3R5 or 5.3R5.1 and being upgraded to any later release (PPS version 5.3R5.2 and above)
1. Login to the active node of the cluster. Go to the menu: System> Clustering > Cluster Status. Select the passive node and click on DISABLE
2. Once the passive node is disabled, you should see this reflected in the cluster status page.
3. You may now upgrade both active and passive nodes in parallel.
4. Once both nodes have been upgraded, login in to active node. Enable the passive node by clicking the ENABLE
5. Once the passive node is enabled, it will sync up with active node and becomes part of the cluster again.