If you're setting up a coordinating node, it shouldn't matter how many master or data nodes you have. The purpose of the coordinating node is to live on the same machine as the Kibana server to distribute the requests to the cluster. The setup of the coordinating node should be the same as the rest of the nodes on the network expect that it shouldn't be a master, data or ingest node. This is accomplished by disabling those in the config:
As long as the
cluster.name matches the rest of your cluster, it's on the same network and can reach the rest of the nodes in the cluster it should automatically join the existing cluster.