MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
MySQL 5.7 supports one status variable providing information about Group Replication. This variable is described here:
group_replication_primary_member
Shows the primary member's UUID when the group is operating in single-primary mode. If the group is operating in multi-primary mode, shows an empty string. See Section 17.5.1.3, “Finding the Primary”.