The user can specify a virtual machine as HA-enabled. By default, all virtual router VMs and Elastic Load Balancing VMs are automatically configured as HA-enabled. When an HA-enabled VM crashes, CloudStack detects the crash and restarts the VM automatically within the same Availability Zone. HA is never performed across different Availability Zones. CloudStack has a conservative policy towards restarting VMs and ensures that there will never be two instances of the same VM running at the same time. The Management Server attempts to start the VM on another Host in the same cluster.

HA features work with iSCSI or NFS primary storage. HA with local storage is not supported.