Class 'Redis' not found when load session driver is redis

Do you find the solution I have the same problem... I use CodeIgniter 3.1.11

MY CONFIG FILE

$config['sess_driver'] = 'redis';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = 'tcp://gml-test.cvfir.0001.euw3.cache.amazonaws.com:6379';
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;

ERROR

An uncaught Exception was encountered
Type: Error
Message: Class 'Redis' not found
Filename: /var/www/gml-app/gml_system/libraries/Session/drivers/Session_redis_driver.php
Line Number: 178
Backtrace:
File: /var/www/gml-app/gml_application/controllers/Welcome.php
Line: 9
Function: __construct
File: /var/www/gml-app/index.php
Line: 310
Function: require_once

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Ok for notice, I found solution: We need install debian package php-redis