Couple of questions regarding this topic. Setup that I have is 4 nodes in Hyper-V. 2 same location and the others in different datacenters. We use the systems databases for all logins. So will need to migrate them as well.
1. When doing an in-place upgrade on an AG what is the rollback?
2. When manually failing over after the 3 secondary nodes are upgraded what happens?
3. Does it failover instantly or does it take it offline and upgrade?