doc: added note about monitor ips update during failover

[kmadac]

Docs update: IP addresses in csi-config-map needs to be changed after failover to secondary site. Without this change, applications can't use mirrored rbd images.

Is there anything that requires special attention

Only documentation update.

Related issues

Fixes: #4493

Future concerns

No future concerns

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• Commit Message Formatting: Commit titles and messages follow
  guidelines in the developer
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• Reviewed the developer guide on Submitting a Pull
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• Pending release
  notes
  updated with breaking and/or notable changes for the next major release.
• Documentation has been updated, if necessary.
• Unit tests have been added, if necessary.
• Integration tests have been added, if necessary.

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[Rakshith-R]

hey @kmadac

The document talks about having a new cluster-mapping.json to provide cephcsi with the required information to map IDs from one cluster to another.

The config.json section does not need to be modified in either cluster.
The configmap's config.json in each k8s cluster can have different config.json entries (mon ips, cluster IDs etc).

Just adding cluster-mapping.json info to each of these k8s cluster's cephcsi configmap is sufficient. The existing cephcsi configmap's config.json does not need to be modified.

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[kmadac]

Sorry @Rakshith-R , I'm not sure I understand your comment. In the issue #4493 we found out that in order to successfully use volumes on secondary site during the failover period, it is necessary to set monitor ip addresses of primary cluster in config.json to secondary monitor ip addresses on secondary k8s cluster. Otherwise we see FailedMount errors in pods which tries to use those volumes.

Check please this comment in the issue: #4493 (comment)