private ResourceInstance createMemberResource(String groupName, String userName) {
    final Map<Resource.Type, String> mapIds = new HashMap<>();
    mapIds.put(Resource.Type.Group, groupName);
    mapIds.put(Resource.Type.Member, userName);
    return createResource(Resource.Type.Member, mapIds);
  }
Create a member resource instance.

@param groupName  group name
@param userName   user name

@return a member resource instance
ambari-server/src/main/java/org/apache/ambari/server/api/services/groups/MemberService.java