I have a three node cluster with a little under 30M events. I have read in some other posts that the process is relatively simple to do an upgrade. I’ll summarize Greg’s comments in a post I found earlier.
Start with non-master nodes.
Bring up with new software
Let join cluster.
Last do Master.
Does this process still hold true? This implies that during this process some nodes will be running 4.0 while the others are running 3.9.3. Is that okay? Additionally, is the 3.9.3 C# API compatible with ES 4.0? I would like to know if I need to schedule an API update with the upgrade or if it’ll be okay for a day or two.