page:

https://pve.proxmox.com/wiki/Cluster_Manager

standart cluster commands

create cluster:

pvecm create CLUSTERNAME

check state of the new cluster:

pvecm status

join node to cluster:

pvecm add IP-ADDRESS-CLUSTER

check:

pvecm status
pvecm nodes

remove a cluster node:

pvecm delnode hp4
 Killing node 4

Kill an old cluster without reinstalling

systemctl stop pve-cluster
systemctl stop corosync

Start the cluster file system again in local mode:

pmxcfs -l

Delete the corosync configuration files:

rm /etc/pve/corosync.conf
rm -r /etc/corosync/*

You can now start the file system again as a normal service:

killall pmxcfs
systemctl start pve-cluster

The node is now separated from the cluster. You can deleted it from any remaining node of the cluster with:

pvecm delnode oldnode
If the command fails due to a loss of quorum in the remaining node, you can set the expected votes to 1 as a workaround:

pvecm expected 1
And then repeat the pvecm delnode command.

Now switch back to the separated node and delete all the remaining cluster files on it. This ensures that the node can be added to another cluster again without problems.

rm /var/lib/corosync/*
As the configuration files from the other nodes are still in the cluster file system, you may want to clean those up too. After making absolutely sure that you have the correct node name, you can simply remove the entire directory recursively from /etc/pve/nodes/NODENAME.