today, I think I finally cracked how to create(drop) a nodegroup. basic concept is to - temporary block gcp - create(drop) the node group - unblock gcp
(the same concept is btw used for adding a starting node to gcp) the block should last for micro seconds
now it's only implementing it...
very happy that I now know how to proceed, I've spent quite a lot of time trying to figure out a 100% safe way of doing it...(wo/ blocking gcp) but this solution will be efficient and fairly easy to implement. (if any protocol dealing with (multi)node-failures can be considered easy)