What is an HA admission control policy?

An HA admission control policy is designed to ensure resources are preserved for scenarios in which virtual machines (VMs) might fail over due to host failures. When a host becomes unavailable, HA admission control guarantees that the remaining hosts have enough resources to restart the VMs that were running on the failed host. This is crucial because if a failure occurs, the VMs need to be quickly and efficiently brought back online, and the admission control policy effectively manages the cluster resources to maintain the desired level of availability.

The policy typically specifies resource reservations based on the total number of powered-on VMs and the expected failover requirements. By doing this, it prevents the situation where there are insufficient resources to accommodate VMs after a failure, thereby maintaining the operational integrity of the virtualized environment.