It is now possible to set up Redis as a session handler for Moodle.
Ensure that the phpredis extension is enabled and working on your sever.

Please place the following lines in config.php
$CFG->session_handler_class = '\core\session\redis';
$CFG->session_redis_save_path = 'tcp://127.0.0.1';

To determine if it has been set correctly, navigate to
$CFG->wwwroot/admin/phpinfo.php and find following the strings in the
session block,

session.save_handler = redis
session.save_path = tcp://127.0.0.1