This article explores how to combine a 2 node Hyper-V cluster and a 2 node application cluster in order to implement a 3 node cluster with real-time replication and automatic failover.
Note that Evidian SafeKit implements a 3 node cluster without Hyper-V on Windows and Linux. The advantage of the 3-node cluster with Hyper-V is that the failover and the failback to the 3rd node are automatic. There is no manual procedure to apply in the SafeKit web console as with the 3 node cluster without Hyper-V.
To implement the solution, 2 SafeKit mirror modules are required:
If server1 fails, the Hyper-V mirror module restarts VM1 on server 3. The application cluster implemented inside VM1 and VM2 now runs between server 2 and server 3. If there is another failure of server 2 or server 3, the application module will manage it and will restart the critical application.
When server1 comes back, the Hyper-V mirror module resynchronizes automatically VM1 on server 1. The resynchronization is made without stopping VM1 on server 3. This failback operation is automatic and does not require any manual operation.
To return to step 1 with VM1 running on server1, either the operator clicks on the swap button of the Hyper-V module in the SafeKit web console. Or by configuration of the Hyper-V module, the swap of VM1 on server1 is automatic.
