ESX High Availability (HA)

High Availability (HA), is a relatively new capability within VMware Infrastructure 3 and is pivotal in eliminating a single point of failure for a mission critical application. When an ESX host goes down (represented by the RED X), the virtual machines running on the failed host, migrate over to the other, healthy ESX hosts with spare capacity. After migration, the virtual machines are restarted automatically and without intervention from the systems administrator.

VMware HA is a leader in the industry and has created an elegant solution to solve the problem of failover at an affordable price. Typically, failover infrastructure is built on complex clustering solutions using expensive hardware. And due to the high price, the traditional solutions is available only to a small percentage of large corporations. VMware HA has implemented an innovative approach that accomplishes the same goal of failover at a reasonable cost, allowing the majority of businesses to take benefit from failover safety and high availability.

At the center of HA is the concept of separating the hardware from the application and OS. By creating a cluster of ESX hosts, the resources of each server is combined to form a resource pool. Virtual machines are created within the cluster where the hardware is separated from the guest OS by a layer of abstraction handled by the Hypervisor.