code: protected function parseConnection($connectionName)
      {
          $connection = null;
  
          // If user provided the connection name read it directly
          if ($connectionName) {
              if (! $connection = config("queue.connections.$connectionName")) {
                  throw new \InvalidArgumentException("Connection '$connectionName' doesn't exist.");
              }
          }
  
          // Try default connection
          if (! $connection) {
              $defaultConnection = config('queue.default');
  
              if ('beanstalkd' == config("queue.connections.$defaultConnection.driver")) {
                  $connection = config("queue.connections.$defaultConnection");
              }
          }
  
          // Try first connection that has beanstalkd driver
          if (! $connection) {
              foreach (config('queue.connections') as $connection) {
                  if ('beanstalkd' == $connection['driver']) {
                      break;
                  }
              }
          }
  
          if (! empty($connection['host'])) {
              $parsedConfigHost = explode(':', $connection['host']);
  
              $this->host = $parsedConfigHost[0];
  
              if (isset($parsedConfigHost[1])) {
                  $this->port = $parsedConfigHost[1];
              }
          }
  
          if (! empty($connection['queue'])) {
              $this->defaultTube = $connection['queue'];
          }
      }
docs: Tries to figure out and set host, port and default tube
  from the Laravel's queue.php config.
  
  @param $connectionName