What vSphere component offers continuous availability for critical virtual machines during a host failure?

The concept of continuous availability for critical virtual machines during a host failure is primarily addressed by vSphere Fault Tolerance. This feature allows a virtual machine to have a live shadow instance that runs on another host, effectively providing uninterrupted service. In the event of a host failure, the enabled virtual machine remains accessible since the shadow instance takes over without any downtime or data loss. This capability is particularly valuable for applications that require high availability, as it ensures that users can always access services without interruption.

While other components mentioned in the choices do provide some form of resiliency or availability, they function differently. vSphere vMotion allows for the live migration of a virtual machine from one host to another without downtime, enhancing operational efficiency but not directly addressing host failure. vSphere Replication aids in disaster recovery by replicating virtual machines to another site or host, but it does not provide immediate failover during an active host failure. vSphere HA, on the other hand, does restart virtual machines on another host in the event of a failure but may involve some downtime during the failover process. Therefore, vSphere Fault Tolerance specifically meets the requirement for continuous availability during host failures.