How Drupal's chained fast backend keeps APCu cache consistent across your web servers

Drupal's cache.backend.chainedfast makes your site faster without any configuration. All you need is to have APCu on your server. It shows up in the bootstrap, config, and discovery cache bins, and most developers never think about it or even know it is being leveraged. The chained-fast backend combines two backends: a fast, inconsistent backend (APCu, local to each web server process) and a…