code: public int getNodeIdForZoneNary(int zoneId, int zoneNary, byte[] key) {
          List<Node> replicatingNodes = this.routingStrategy.routeRequest(key);
          int zoneNAry = -1;
          for(Node node: replicatingNodes) {
              // bump up the counter if we encounter a replica in the given zone;
              // return current node if counter now matches requested
              if(node.getZoneId() == zoneId) {
                  zoneNAry++;
  
                  if(zoneNAry == zoneNary) {
                      return node.getId();
                  }
              }
          }
          if(zoneNAry == -1) {
              throw new VoldemortException("Could not find any replicas for the key "
                                           + ByteUtils.toHexString(key) + " in given zone " + zoneId);
          } else {
              throw new VoldemortException("Could not find " + (zoneNary + 1)
                                           + " replicas for the key " + ByteUtils.toHexString(key)
                                           + " in given zone " + zoneId + ". Only found "
                                           + (zoneNAry + 1));
          }
      }
docs: TODO: add unit test.