public static List<String> getDisabledReplicas(ZNRecord znRecord) {
    List<String> disabledReplicas = znRecord.getListField(ClusterMapUtils.DISABLED_REPLICAS_STR);
    return disabledReplicas == null ? new ArrayList<>() : disabledReplicas;
  }
Get the list of disabled replicas on a given instance. This is guaranteed to return a non-null list. It would return
an empty list if there are no disabled replicas or if the field itself is absent for this instance.
@param znRecord the {@link ZNRecord} associated with the interested instance.
@return the list of disabled replicas.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/ClusterMapUtils.java