code: function (loadBalancer, type, callback) {
      var self = this,
          loadBalancerId =
            loadBalancer instanceof lb.LoadBalancer ? loadBalancer.id : loadBalancer;
  
      if (!type || (type !== 'HTTP_COOKIE' && type !== 'SOURCE_IP')) {
        throw new Error('Please provide a valid session persistence type');
      }
  
      self._request({
        path: urlJoin(_urlPrefix, loadBalancerId, 'sessionpersistence'),
        method: 'PUT',
        body: {
          sessionPersistence: {
            persistenceType: type
          }
        }
      }, function (err) {
        return callback(err);
      });
    }
docs: client.enableSessionPersistence
  
  @description Enable session persistence of the requested type
  
  @param {Object}          loadBalancer      the loadBalancer or loadBalancerId
  @param {String}          type              HTTP_COOKIE or SOURCE_IP
  @param {function}        callback