private static List<String> separateByComma(ConfigHelper config, Cluster cluster, String propertyName) {
    String propertyValue = config.getValueFromDesiredConfigurations(cluster, ConfigHelper.HDFS_SITE, propertyName);
    return isBlank(propertyValue)
      ? Collections.emptyList()
      : Arrays.asList(propertyValue.split(","));
  }
NameNodes in this nameservice.
The minimum number of NameNodes for HA is two, but more can be configured.
ambari-server/src/main/java/org/apache/ambari/server/stack/NameService.java