code: public static Endpoint selectNode(ClientRequestContext ctx, String groupName) {
          groupName = normalizeGroupName(groupName);
          final EndpointSelector endpointSelector = getNodeSelector(groupName);
          if (endpointSelector == null) {
              throw new EndpointGroupException("non-existent EndpointGroup: " + groupName);
          }
  
          return endpointSelector.select(ctx);
      }
docs: Selects an {@link Endpoint} from the {@link EndpointGroup} associated with the specified
  {@link ClientRequestContext} and case-insensitive {@code groupName}.