I am interested in the two features named "Fault Tolerance" and "App High Availability" which are part of some VMware products. As far as I understand the vCenter Server instance is needed to perform administrative tasks. Therefore, a crash of the vCenter Server makes it impossible to modify certain aspects of the VMs, but the VMs still run.
I also found out that the "HA" feature still works (with some minor limitations) even when no vCenter Server is running.
Now, my questions:
What happens to a VM which is configured to use FT if the vCenter Server is offline and the host of the primary VM is offline? Ideally, FT would take care to seamlessly continue the VMs operation on the secondary host.
What happens to a VM which is configured to use App HA if the vCenter Server is offline and the app inside the VM crashes? Ideally, the app crash would be detected and depending on the configuration the app or the whole VM would be restarted.
Best Answer
Some of this is covered in the vSphere HA Technical Deep-Dive...
But to summarize, vSphere installs HA agents on the hosts when you enable HA. vCenter is not required for HA to function. vCenter is needed in order to make changes to the cluster configuration, however, HA restarts follow a set prioritization schedule.
The point is that these things HAVE to be able to work without vCenter. E.g. the situation in which the host containing the vCenter fails needs to be covered (since it's highly-probable), and is.