Redis Sessions for and Service Decorators in Drupal 8

Goal: Getting PHP Sessions into Redis

One of several performance-related goals for was to get the production database to a read-only state. This included moving cache, the Dependency Injection container, and the key-value database table to Redis.  99% of all sessions were for logged-in users, which use a separate, internal instance of Drupal; but there are edge cases where anonymous users can still trigger a PHP session that gets saved to the database.