code: public function askSlotMap(NodeConnectionInterface $connection = null)
      {
          if (!$connection && !$connection = $this->getRandomConnection()) {
              return;
          }
  
          $this->slotmap->reset();
  
          $response = $this->queryClusterNodeForSlotMap($connection);
  
          foreach ($response as $slots) {
              // We only support master servers for now, so we ignore subsequent
              // elements in the $slots array identifying slaves.
              list($start, $end, $master) = $slots;
  
              if ($master[0] === '') {
                  $this->slotmap->setSlots($start, $end, (string) $connection);
              } else {
                  $this->slotmap->setSlots($start, $end, "{$master[0]}:{$master[1]}");
              }
          }
      }
docs: Generates an updated slots map fetching the cluster configuration using
  the CLUSTER SLOTS command against the specified node or a random one from
  the pool.
  
  @param NodeConnectionInterface $connection Optional connection instance.