VMware HA leverages multiple ESX/ESXi hosts configured as a cluster to provide rapid recovery from outages and cost-effective high availability for applications running in virtual machines.

VMware HA protects application availability in two ways:

It protects against a server failure by automatically restarting the virtual machines on other hosts within the cluster.

It protects against application failure by continuously monitoring a virtual machine and resetting it in the event that a failure is detected.

Unlike other clustering solutions, VMware HA provides the infrastructure to protect all workloads with the infrastructure:

No special software needs to be installed within the application or virtual machine. All workloads are protected by VMware HA. After VMware HA is configured, no actions are required to protect new virtual machines. They are automatically protected.

VMware HA can be combined with VMware Distributed Resource Scheduler (DRS) not only to protect against failures but also to provide load balancing across the hosts within a cluster.

VMware HA has a number of advantages over traditional failover solutions:

Minimal setup

After a VMware HA cluster is set up, all virtual machines in the cluster get failover support without additional configuration.

Reduced hardware cost and setup

The virtual machine acts as a portable container for the applications and it can be moved among hosts. Administrators avoid duplicate configurations on multiple machines. When you use VMware HA, you must have sufficient resources to fail over the number of hosts you want to protect with VMware HA. However, the vCenter Server system automatically manages resources and configures clusters.

Increased application availability

Any application running inside a virtual machine has access to increased availability. Because the virtual machine can recover from hardware failure, all applications that start at boot have increased availability without increased computing needs, even if the application is not itself a clustered application. By monitoring and responding to VMware Tools heartbeats and resetting non-responsive virtual machines, it also protects against guest operating system crashes.

DRS and VMotion integration

If a host fails and virtual machines are restarted on other hosts, DRS can provide migration recommendations or migrate virtual machines for balanced resource allocation. If one or both of the source and destination hosts of a migration fail, VMware HA can help recover from that failure.