Joining a cluster with already created guests VM

[Ramalama]

For now, yes.

We need some kind of new multi-cluster gui interface, not yet available.

i couldn't better say it.
then the world of proxmox would be amazing.

 

[markusbernhard]

I have a work-around that *might* work for you, but has not been thoroughly tested.
There is a firm requirement however that there must not be any conflicts with the guest ID, or the node name.

On node1 (with guests)
Create a new cluster or get join information.

On node2 (with guests)
scp -r /etc/pve/nodes/* to node1:/etc/pve/nodes
rm -r /etc/pve/nodes/*
Join cluster.

Please realize there is potential for things to go sideways!
I've done this to re-assemble a cluster I've recently had to pick apart, and can't provide any details on long-term issues or risk.
I cannot suggest this work-around at the moment for nodes that have never been in a cluster with each other.
I've done this with online VMs! and they remain operational through the process. The join cluster process will overwrite the contents of /etc/pve/nodes with copies from the cluster... so copying your new node directory to the cluster with scp will indirectly restore it on cluster join.

Good luck.

Thanks, it worked just fine!
I also backed up storage.cfg on joining node and appended the contents to the cluster storage.cfg.