vSphere HA leverages multiple ESXi hosts configured as a cluster to provide rapid recovery from outages and cost-effective high availability for applications running in virtual machines.
vSphere HA protects application availability in the following ways:
It protects against a server failure by 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.
It protects against datastore accessibility failures by restarting affected virtual machines on other hosts which still have access to their datastores.
It protects virtual machines against network isolation by restarting them if their host becomes isolated on the management or Virtual SAN network. This protection is provided even if the network has become partitioned.
Unlike other clustering solutions, vSphere HA provides the infrastructure to protect all workloads with the infrastructure:
You do not need to install special software within the application or virtual machine. All workloads are protected by vSphere HA. After vSphere HA is configured, no actions are required to protect new virtual machines. They are automatically protected.
You can combine vSphere HA with vSphere Distributed Resource Scheduler (DRS) to protect against failures and to provide load balancing across the hosts within a cluster.
vSphere HA has several advantages over traditional failover solutions:
After a vSphere 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 vSphere HA, you must have sufficient resources to fail over the number of hosts you want to protect with vSphere 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 restarting nonresponsive virtual machines, it 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, vSphere HA can help recover from that failure.