VMware HA supports high availability for virtual machines by pooling the hosts they reside on into a cluster. If one host fails, its virtual machines move to a different host in the cluster.
VMware HA monitors ESXi hosts and in the event of host failure, migrates virtual machines to hosts with capacity. When you add new virtual machines to a VMware HA cluster, VMware HA checks whether enough capacity to power on that virtual machine is available on that host or a different host.
See Managing HA Clusters.
