Can 6.5.2 indexers co-exist with 7.1.2 indexers?

[louieb3]

I will be upgrading 4 indexers from 6.5.2 to 7.1.2. Will I need to stop all 4 indexers, upgrade them all, and then start them all again on the same version? Or can I stop indexer1, upgrade, start, and then do the same for the rest of the indexers? In other words, can 6.5.2 indexers co-exist with 7.1.2 indexers?

Thanks in advance.

[Lazarix]

Follow This Guide on how to upgrade a cluster, with various options depending on your topology.
In future versions (but not applicable for this scenario), you will be able to perform Rolling Upgrades

[renjith_nair]

Is it a distributed or cluster environment?

[louieb3]

It's distributed.

[richgalloway]

You should be fine in a distributed environment.

[renjith_nair]

As per http://docs.splunk.com/Documentation/Splunk/7.1.2/Installation/UpgradeyourdistributedSplunkEnterpris..., you could follow this approach

(Optional if you do not have downtime concerns) Choose an indexer to keep the environment running, and designate it as "Indexer #1".
(Optional if you do not have downtime concerns) Choose a second indexer to upgrade, and designate it as "Indexer #2."
If you need to maintain uptime, bring down all of the indexers except Indexer #1. Otherwise, bring all indexers down and continue at Step 7.
Upgrade Indexer #2.
Bring up Indexer #2 and test for operation and functionality.
Once you have confirmed proper operation on Indexer #2, bring down Indexer #1.
Upgrade Indexer #1 and all of the remaining indexers, one by one. You can restart the indexers immediately after you upgrade them.
Confirm operation and functionality across all of the indexers.
Restart the deployment server, and confirm its operation and functionality.

You might also need to check the forwarder - indexer compatibility ,especially between 6 & 7

http://docs.splunk.com/Documentation/Forwarder/7.1.2/Forwarder/Compatibilitybetweenforwardersandinde...