What is the minimum number of ESXi hosts required in a vSphere Cluster to use vSphere HA?

To implement vSphere High Availability (HA), a minimum requirement is to have at least two ESXi hosts in a cluster. This configuration allows for proper failover capabilities; when one host fails, the virtual machines (VMs) running on that host can be quickly restarted on the remaining host. With just a single host, there would be no redundancy—if that host fails, there is nowhere for the VMs to failover to, thus undermining the purpose of HA, which is to maintain availability.

Having two hosts ensures that you have enough resources to support failover scenarios while also permitting the heartbeat mechanism that vSphere HA uses to monitor host status. In the context of a typical deployment, three hosts are often recommended to provide even greater fault tolerance and resource management; however, the essential minimum requirement remains two hosts to fulfill the HA functionality.