Here is a recommended order of operations for upgrading Gravwell.
We generally recommend bringing the indexers up first and the webservers shortly thereafter.
While the ingesters are highly flexible on versions and protocol handling, the webservers, indexers, and searchagent components are much more coupled.
Our general upgrade operation is as follows:
1. Upgrade indexer
2. Upgrade webserver
3. Upgrade searchagent
4. Upgrade ingesters
If you have multiple sites we also recommend upgrading one site at a time, validating operations, then upgrading the other.