ESXi hosts are licensed with vSphere licenses. Each vSphere license has a certain CPU capacity that you can use to license multiple physical CPUs on ESXi hosts. When you assign a vSphere license to a host, the amount of CPU capacity consumed equals the number of physical CPUs in the host. vSphere Desktop that is intended for VDI environments is licensed on per virtual machine basis.
To license an ESXi host, you must assign it a vSphere license that meets the following prerequisites:
The license must have sufficient CPU capacity to license all physical CPUs on the host. For example, to license two ESXi hosts that have four CPUs each, you need a vSphere license with a minimum capacity of 8 CPUs to the hosts.
The license must support all the features that the host uses. For example, if the host is associated with a vSphere Distributed Switch, the license that you assign must support the vSphere Distributed Switch feature.
If you attempt to assign a license that has insufficient capacity or does not support the features that the host uses, the license assignment fails.
You can assign and reassign the CPU capacity of a vSphere license to any combination of ESXi hosts. You can assign a vSphere license for 10 CPUs to any of the following combinations of hosts:
Five 2-CPU hosts
Three 2-CPU hosts and one 4-CPU host
Two 4-CPU hosts and one 2-CPU host
One 8-CPU host and one 2-CPU host
Dual-core and quad-core CPUs, such as Intel CPUs that combine two or four independent CPUs on a single chip, count as one CPU.
When you install ESXi, its default license is evaluation mode. Evaluation mode licenses expire after 60 days. An evaluation mode license provides the set of features that equals the highest vSphere product edition.
If you assign a license to an ESXi host before its evaluation period expires, the time available in the evaluation period decreases by the time already used. To explore the entire set of features available for the host, set it back to evaluation mode, and use it for the remaining evaluation period.
For example, if you use an ESXi host in evaluation mode for 20 days, then assign a vSphere Standard license to the host, and then set the host back to evaluation mode, you can explore the entire set of features available for the host for the remaining evaluation period of 40 days.
License and Evaluation Period Expiry
For ESXi hosts, license or evaluation period expiry leads to disconnection from vCenter Server. All powered on virtual machines continue to work, but you cannot power on virtual machines after they are powered off. You cannot change the current configuration of the features that are in use. You cannot use the features that remained unused while the host was in evaluation mode.
Licensing ESXi Hosts After Upgrade
If you upgrade an ESXi host to a version that starts with the same number, you do not need to replace the existing license with a new one. For example, if you upgrade a host from ESXi 5.1 to 5.5, you can use the same license for the host.
If you upgrade an ESXi host to a version that starts with a different number, you must apply a new license. For example, if you upgrade an ESXi host from 5.x to 6.x, you need to license the host with a vSphere 6 license.
vSphere Desktop is intended for VDI environments such as Horizon View. The license usage for vSphere Desktop equals the total number of powered on desktop virtual machines running on the hosts that are assigned a vSphere Desktop license.