docs: public List<InstanceInfo> getInstancesByVirtualHostName(String virtualHostName) {
          return Optional.ofNullable(this.virtualHostNameAppMap.get(virtualHostName.toUpperCase(Locale.ROOT)))
              .map(VipIndexSupport::getVipList)
              .map(AtomicReference::get)
              .orElseGet(Collections::emptyList); 
      }