Issue 153: Add Rollback support for Pravega Cluster

[pbelgundi]

Signed-off-by: pbelgundi [email protected]

Change log description

• Support for manual rollback of Pravega cluster to the previous version when upgrade fails.
• Rollback can be done only to previous cluster version and only when cluster in 'Upgrade Failed' state.
• Added version history field to Pravega Cluster Status. This would store history of all versions through which PravegaCluster has been successfully upgraded so far. ( similar to kubectl rollout history ). The last value in this array would be same as Current Version.
• Improvements to Upgrade: When cluster upgrade is in progress, Cluster Status condition "Upgrading" is set to true and Reason and message values are set to indicate component currently being upgraded and number of replicas for which upgrade has completed against total replicas in component.
• Removed all occurrences of spec.version assignment from operator code.
• Added documentation for rollback.

Purpose of the change

Fixes #153

How to verify it

1. Rollback is triggered when Upgrade fails and user manually updates the spec.version field to the previous version.
2. When Rollback is in progress cluster condition RollbackInProgress set to Status=true.
3. Rollback of Pravega cluster to the previous version completes successfully for all Pravega Components.
   This is indicated by all pravega replicas moving back to the older version and re-starting successfully.
   Tested rollback after a failing upgrade in each component - bookkeeper, controller and segmentstore and in all 3 cases the cluster was successfully restored back to the previous version.
4. Incase of Rollback Failure, Cluster Status is set to Condition Error with Status=true and Reason = RollbackFailed and manual intervention would be needed to recover from this state.

[bourgeoisor]

Thanks for modifying the flow to cater mostly to manual upgrade, Prajakta! Some of these tweaks are also really helpful, like the enhanced statuses. I have gone through the diff and this approach seems good to me. That being said, I would like someone else to approve in my stead, mainly due to my lack of deep understanding of the Pravega codebase and practices.

[pbelgundi]

Thanks for modifying the flow to cater mostly to manual upgrade, Prajakta! Some of these tweaks are also really helpful, like the enhanced statuses. I have gone through the diff and this approach seems good to me. That being said, I would like someone else to approve in my stead, mainly due to my lack of deep understanding of the Pravega codebase and practices.

@bourgeoisor, thanks for your comments.
I have added @fpj as a reviewer.

[EronWright]

I don't have time to look at the details, but the main issue that I mentioned earlier has been resolved (thank you!).