Craft 3 Redis configuration error when following the information for enabling Redis in Craft 3, my site just refreshes to a blank screen with a "Internal server error" generic message. Reviewing the server logs reveals:

ReflectionException: Class yii\redis\Cache does not exist in /storage/path/www/staging_html/vendor/yiisoft/yii2/di/Container.php:428


Talking with my hosting provider (Arcustech), informs me that Redis is indeed running and php-redis is installed. The details I entered into config\app.php were

return [
'components' =&gt; [
    'cache' =&gt; [
        'class' =&gt; yii\redis\Cache::class,
        'defaultDuration' =&gt; 86400,
        'redis' =&gt; [
            'hostname' =&gt; 'localhost',
            'port' =&gt; 6379,
            'database' =&gt; 0,
        ],
    ],
  ],
];


Any light that could be shone onto my predicament would be amazing.
thanks!
Turns out it was a beginners mistake, thank you to Robin in the comments above for setting me on the right track. All that was required to install was the Yii2 library, once this was done all worked as expected.