VMware vSphere High Availability (HA) is a feature of VMware vSphere, a leading virtualization platform, that provides automated failover and high availability for virtual machines (VMs) running on VMware ESXi hosts. Let’s explore its history and features:

History of VMware vSphere High Availability (HA):
– VMware vSphere High Availability (HA) was first introduced as part of VMware ESX 2.5 in 2005, and it has been a key feature of VMware vSphere ever since.
– The initial goal of HA was to provide automated restart capabilities for VMs in the event of a host failure, ensuring minimal downtime and improved availability for virtualized environments.
– Over the years, VMware has continuously enhanced the HA feature, introducing new capabilities and improvements to make it even more robust and reliable.

Features of VMware vSphere High Availability (HA):
1. Automated Failover: HA provides automated failover for VMs in the event of a host failure. If a host goes down, the VMs running on that host are automatically restarted on other healthy hosts within the cluster, ensuring uninterrupted service availability.
2. Host Monitoring: HA continuously monitors the health and availability of ESXi hosts in the cluster. It detects host failures or network isolation events and triggers the failover process to restart affected VMs on other hosts.
3. Admission Control: HA incorporates admission control policies to ensure that sufficient resources are available in the cluster to support VM restarts in the event of a host failure. It prevents overcommitment of resources and ensures that VMs have enough capacity to run on other hosts.
4. Datastore Heartbeating: HA uses datastore heartbeating as a mechanism to detect host failures. It monitors the accessibility of shared datastores across hosts and considers a host failed if it loses connectivity to its designated datastore.
5. Proactive HA: Proactive HA is an advanced feature that allows for proactive monitoring and evacuation of hosts before they fail. It uses hardware monitoring and health checks to identify potential host issues and migrates VMs to healthy hosts preemptively.
6. VM Monitoring: HA can monitor the heartbeats of individual VMs to detect guest OS or application failures. If a VM’s heartbeat is not received, HA can initiate a restart of the VM on another host to recover from the failure.
7. Integration with Distributed Resource Scheduler (DRS): HA integrates with VMware’s Distributed Resource Scheduler (DRS) to provide intelligent VM placement during failover. DRS ensures that the VMs are placed on hosts with sufficient resources and optimal load balancing.
8. Integration with vCenter Server: HA is fully integrated with vCenter Server, allowing for centralized management and configuration of HA settings. vCenter Server provides a single pane of glass for monitoring, configuring, and troubleshooting HA clusters.
9. Orchestrated Restart: HA provides an orchestrated restart process to ensure a controlled and orderly startup of VMs after a host failure. It prioritizes VM restarts based on resource availability and configurable restart priorities.
10. Proven Reliability: VMware vSphere High Availability (HA) is a mature and widely adopted solution, with a proven track record of delivering high availability for virtualized environments. It is a trusted technology used by organizations across industries to minimize downtime and ensure business continuity.

VMware vSphere High Availability (HA) is a critical feature for ensuring the availability and resilience of VMs in VMware vSphere environments. Its automated failover capabilities, integration with vCenter Server, and proactive monitoring make it a valuable tool for maintaining high availability and minimizing downtime in virtualized infrastructures.