I got a functional 2 nodes cluster. I provide two more VM as new nodes and when i try to add this VM as nodes by modifying the cluster.yml with unique role: worker for each of them the cluster failed with some error like this
WARN[0005] Can’t start Docker container [rke-cp-port-listener] on host [IP-OF-MASTER-NODE]: Error response from daemon: driver failed programming external connectivity on endpoint rke-cp-port-listener (3bc8826acc2b247a57a1ed12bfa5a106255d41298440b6c2c93b34c687c7ffa1): Error starting userland proxy: listen tcp 0.0.0.0:6443: bind: address already in use