A vSphere administrator sees the alarm: vSphere HA virtual machine failed to failover This occurred for virtual machines (VMs) in a cluster with vSphere High Availability (HA) enabled. The guest opera

If an ESXi host is running but has become isolated from the network, for instance due to a management network failure, vSphere HA cannot communicate with the host or determine the state of its VMs. This host isolation prevents HA from initiating or completing the failover of virtual machines to other healthy hosts, resulting in the reported alarm because the guest OS itself would not report a power failure since the VM is technically still powered on on the isolated host.

Incomplete VM cloning operations are unrelated to vSphere HA failing to failover existing running VMs in response to a host issue; cloning problems would manifest during the cloning process itself.

vCenter Server reboots typically do not impact the ongoing operation of vSphere HA, as HA agents on ESXi hosts are designed to handle failover independently once HA is configured, even if vCenter Server is unavailable.

Errors during a vSphere vMotion migration would trigger specific vMotion alarms and might affect the VM's status but are not the direct cause of an HA failover failure related to a host's network isolation or failure.