vSphere High Availability (HA) ensures availability of the virtual machines in your SDDC. If a host fails, vSphere HA restarts its VMs on a different host. All clusters in a VMware Cloud on Public Cloud SDDC are configured to use vSphere HA. This setting cannot be reconfigured.
To ensure availability of all workload and management VMs in your SDDC,
VMware Cloud on Public Cloud must maintain sufficient capacity to power them on in the event of host failure. HA admission control is the primary mechanism for capacity maintenance. Admission control imposes constraints on resource usage, and can prevent any action that consumes more resources than the cluster can support during a failover. These constraints apply to actions like powering on or migrating a VM, or reserving additional CPU or memory resources for a VM, and effectively limit the availability of host resources as shown here:
- In a two-host SDDC cluster, admission control prevents you from powering-on more than 36 VMs or assigning more than 1152 MHz CPU reservation to a single VM.
- In SDDC clusters with three to five hosts, admission control reserves one host for failover.
For a detailed discussion of vSphere HA and other features that ensure vSphere availability, see How vSphere HA Works in the VMware vSphere Product Documentation. Although most HA settings in VMware Cloud on Public Cloud are managed for you by VMware and cannot be changed in your SDDC's vCenter Server, it's important to understand the fundamental concepts of vSphere HA and how they apply to workload deployment in your SDDC.
