I have 2 ACS 3.2 servers that I want to upgrade to 4.2.1, the latest version before 5, as I understand.
My question is regarding replication. Do I need to stop database replication and upgrade the servers separately or not? Can I upgrade the servers while database replication is configured? If so, is there an specific order of upgrade?
Here is the note from the User guide.
"All ACSs that are involved in replication must run the same release of the ACS software. For example, if the primary ACS is running ACS version 3.2, all secondary ACSs should be running ACS version 3.2. Because patch releases can introduce significant changes to the ACS internal database, we strongly recommend that ACSs involved in replication use the same patch level."
So, I would suggest you to disable replication before upgrading. After all ACS are upgraded to the same version, you can enable replication again.