code: GatewayServer roundrobin(List<GatewayServer> list) {
          int index = this.seq.getAndIncrement();
          if(index < 0) {
              this.seq.set(0);
              index = 0;
          }
  
          final int size = list.size();
          if (index != 0 && index >= size) {
              index = index % size;
          }
  
          return list.get(index);
      }
docs: Roundrobin.
  
  @param list the list
  @return the gateway server