Acquia Developer Portal Blog: Drupal Cache Strategy with Varnish and Edge CDN on Acquia

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The requirement is to cache content for as long as possible, but update promptly when content changes are made in Drupal. 

Note that in this setup I’m using Acquia Edge powered by Cloudflare, but the strategy would be similar for Acquia Edge powered by Akamai.

The objective is to bootstrap Drupal as infrequently as possible, by relying on the Varnish and CDN layers, but always to serve fresh content: Cache pages in Varnish for a long time, but provide a method (Purge) to invalidate Varnish when a content change is made in Drupal. At the CDN layer, the goal is to make sure the current version of a page is delivered to the browser, by checking Varnish frequently to see if a new version is available. This check is a lightweight call to Varnish. If Varnish does not have a new version, the CDN-cached version is delivered.

Drupal Modules: