Hi sahabhi606,
In terms of steps:
1. Test your apps and make sure they are compatible with 8.0 (you need to go to Splunk base and check if they are compatible)
2. Upgrade Deployment Server (disable it first, then upgrade, do not restart it yet)
3. Upgrade Search Heads
4. Upgrade Indexers (once completed you can now restart your deployment server)
5. Upgrade Forwarders
While upgrading the indexer cluster follows steps mentioned in:
https://docs.splunk.com/Documentation/Splunk/8.0.1/Indexer/Upgradeacluster
While upgrading the search cluster follows steps mentioned in:
https://docs.splunk.com/Documentation/Splunk/8.0.1/DistSearch/UpgradeaSHC
For more info:
https://docs.splunk.com/Documentation/Splunk/8.0.1/Installation/UpgradeyourdistributedSplunkEnterpriseenvironment#Upgrade_a_distributed_environment_with_multiple_indexers_and_non-pooled_search_heads
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