eEVOS Plus is licensed per CPU (unlimited cores).
Smallest license would be 1 CPU which allows installation on one server.
For the high availability at least 2 CPU licenses are required (one CPU per node).
Licenses must be kept in pairs and the amount of the CPUs must be the same on each individual node.
4 CPU license allows either 4 CPU single server or 2 Servers with 2 CPUs.
You can use motherboard with several CPU sockets – as long as these are not populated you will not be asked for additional license. This way you can later install additional CPUs and upgrade your license.