agaric-coop/box/docs/extras/redis.md

Redis is an in-memory caching system, much like Memcached. While Varnish is generally used to improve performance for anonymous users, redis is used to improve the performance for logged in users.

To enable Redis in Drupal VM:

1. Make sure redis is in the list of installed_extras in your config.yml.
2. Install the Redis module.
3. Enable the module before you configure it in the next step.
4. Add the following to your settings.php

// Make redis the default cache class.
$settings['cache']['default'] = 'cache.backend.redis'

There's a lot more configuration available and the best resource is generally the Redis module's README.

For a list of available role variables, see the geerlingguy.redis Ansible role's README.