Prerequisite:
You need to know how to SSH.
and/or
Need to know how to work in the Linux terminal.
Basic Linux knowledge.
A minimum of 2 servers (virtual or physical)
The servers must be connected to the same network.

NOTE: If you want to use High Availability, you need 3 servers.

This can be done from the terminal or the WebUI. I’ll be using the terminal.

Proxmox has a tool for doing this called PVECM (Proxmox Virtual Environment Cluster Manager).
First, you need to SSH to one of your servers, or use the terminal from the WebUI.

1. To create the cluster, type:
   pvecm create VECluster01
   You can replace the VECluster01 with the name you want for your cluster.
2. From the other server, you need to type:
   pvecm add pve1
   instead of pve1 write the hostname, or the IP address of your other server that is already in the cluster.

You can check the cluster by typing:
pvecm status