Let's say that you have purchased a new node and you wish to make it part of your existing cluster, how would you do that?
A cluster is a collection of nodes. You can add new nodes to a cluster at any time after physically installing and connecting them to the network on the same subnet as the cluster. The cluster expansion process compares the AOS version on the existing and new nodes and performs any upgrades necessary for all nodes to have the same AOS version.
The process for adding a node varies depending on the AOS version, hypervisor type (AHV, ESXi, Hyper-V, or Citrix Hypervisor), data-at-rest encryption status, and certain hardware configuration factors.
Here is the guide to expand a cluster that explains the expansion process and the pre & post checks: expanding a cluster
Before you start it's better to check this doc before attempting to add a node to the cluster since the process of adding a node varies depending on several factors considerations based on your AOS, hypervisor, encryption, and hardware configuration.
What if you want to expand a one-node or two-nodes cluster?
You will have to destroy the cluster and create a new one with the new node since expansion is not possible for clusters that are smaller than 3 nodes.
Check out KB-5943 for more information.