MySQL 5.7 Reference Manual
MySQL 5.7 Release Notes
This section describes how to add NDB Cluster data nodes “online”—that is, without needing to shut down the cluster completely and restart it as part of the process.
Currently, you must add new data nodes to an NDB Cluster as part of a new node group. In addition, it is not possible to change the number of fragment replicas (or the number of nodes per node group) online.