What defines a vSphere cluster?

A vSphere cluster is defined as a group of ESXi hosts that work together to provide resource management and redundancy. This configuration allows for the pooling of computing resources from multiple servers, which enhances efficiency, scalability, and availability. By using a cluster, administrators can distribute workloads across several hosts, ensuring that if one host fails, the virtual machines (VMs) running on that host can be automatically migrated to other hosts within the cluster without downtime. This capability is part of VMware's High Availability (HA) and Distributed Resource Scheduler (DRS) features, which promote optimal performance and reliability in a virtualized environment.

The primary goal of implementing a vSphere cluster is to ensure that resources are used effectively while also providing a safety net for VMs in case of hardware failures. Thus, the collaborative nature of the ESXi hosts in a cluster is what fundamentally distinguishes it from standalone hosts or other configurations.