We have WSFC with 4 nodes + a file share witness.
Only nodes 1-3 have SQL server on it with Availability Groups (AGs), and node 4 is shut down gracefully.
Node 1 has the primary AAG server.
Now, we recently had an uncontrollable outage for which the only thing we know for certain is that nodes 1 and 2 were together with power supply and network, but nodes 3-4, and the witness, were cut off - but probably still up.
Since the power supply renewed, WSFC is showing results that I don't understand:
- Current host server is Node 3;
- In Cluster Core Resources, IP addresses that belong to nodes 1 and 2, are shown as down;
- In Nodes section, nodes 1-3 are shown as up, and node 4 down (as expected);
BUT: The primary AG server is still on node 1 as it was before, and it accepts read/write connections as usually.
This make me doubt if I understand correctly how WSFC and AGs work together.
- Should not the current WSFC host also be the primary AG server?
- How does the listener work? In our case, we have multi-subnet networking, and the listener's DNS name always resolves to 3 IP addresses among which one belongs to the current primary AG server, and works for connections. Does WSFC determine the listener's addresses?
- Is there any other principle (except quorum) that AG depends on WSFC?