Can we upgrade the Indexer Cluster and Cluster Master with no downtime?
As per our security regulatory requirements we cannot have downtime for Splunk upgrade.
We will be upgrading from 6.5.3to 7.1.6
If yes, can you share the procedure.
It depends on your definition of downtime. The cluster master cannot be upgraded without being restarted. During the restart it is "down", but the indexer cluster will continue to function.
The cluster itself can also be upgraded one indexer at a time, but each indexer must be down for a short time. If your replication and search factors are at least 2 then the cluster will continue to index data and process searches.
The procedure for upgrading a cluster is documented at https://docs.splunk.com/Documentation/Splunk/7.3.0/Indexer/Upgradeacluster.
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