Phase 5: Decide to continue or abandon the upgrade
If you encounter problems such as application errors, nodes failing to start, or unexplainable behavior that prevent you from completing the upgrade, you have the option to roll back the cluster to the previous version of Cassandra.
If you encounter problems that prevent you from safely completing the upgrade, see Roll back an upgrade for instructions on how to roll back Cassandra to the previous version.
At the end of this phase:
Cassandra is in a healthy state and all nodes are running the new version. If your cluster is working well, proceed to Phase 6: Upgrade SSTables to new file format.
The upgrade failed and Cassandra has been rolled back to the previous version. If you rolled back the upgrade, proceed to Phase 7: Clean up after upgrade or rollback.