State of knowledge

February 2021

Virtualization and VMware vSphere HA support

There is no special support for VMware vSphere High Availability (HA) built into our software.

VMware vSphare High Availability (HA) support goes hand in hand with service outages, i.e. services fail and are only brought back online as soon as possible.

Cold standby licenses are required.

Notes on high availability/failure safety

A highly available system is a system that is continuously in operation for an optimal period of time. There are several ways to achieve high availability for systems, such as using HA applications, redundant NICs, server clusters, redundant power supplies, and so on. You can also achieve high availability at the virtualization level. In vSphere, a feature called vSphere High Availability is used to achieve high availability at the virtualization level.

Many people mistakenly confuse VMware vSphere High Availability (HA) with fault tolerance. 
VMware vSphere High Availability (HA) is not fault-tolerant because if one host fails, the VMs on it also fail. HA only deals with restarting those VMs on other ESX/ESXi hosts with sufficient resources.
Fault tolerance, on the other hand, provides uninterrupted access to resources in the event of a host failure.


VMware vSphere High Availability (HA) maintains a communication channel with all other ESX/ESXi hosts that are members of the same cluster by using a heartbeat that is sent every 1 second in vSphere 4.0 and every 10 seconds by default in vSphere 4.1. If an ESX Server misses a heartbeat, the other hosts wait 15 seconds for the other host to respond again. After 15 seconds, the cluster initiates the restart of the VMs on the failing ESX/ESXi host on the remaining ESX/ESXi hosts in the cluster. VMware vSphare High Availability (HA) also constantly monitors the ESX/ESXi hosts that are members of the cluster and ensures that resources are always available to meet the requirements in the event of a host failure.

Failure protection

VMware vSphere High Availability (HA) protects against the following types of failures:

  • Failure of an ESXi host
    If an ESXi host fails, VMs running on that host are automatically restarted on other ESXi hosts.
  • Guest operating system failure
    If the VM Monitoring option is enabled and the VM stops sending heartbeats, the guest OS is reset. The VM remains on the same ESXi host.
  • Application failure and monitoring agent
    The agent on an ESXi host can monitor the heartbeats of applications running inside a VM. If an application fails, the VM is restarted but remains on the same host. This type of monitoring requires a third-party application monitoring agent and VMware tools.