Drupal Cache Invalidation Strategies That Scale Across Redis, Varnish, and Akamai

In this technical post, Wassim Ben Sassi presents a detailed guide to cache invalidation strategies for enterprise‑scale Drupal sites. Instead of a simple “just cache it” approach, he breaks caching into multiple layers: browser, CDN (such as Akamai), reverse proxies like Varnish, application caches using Redis or Memcache, and Drupal’s own internal caches. Cache tags and contexts form the foundation of this structure, enabling precise invalidation of outdated or changing content. The post includes practical code examples for defining custom tags and contexts, and shows how TempStore can be used for user‑specific transient data, especially when backed by Redis for performance.

Beyond Drupal’s internal cache system, the post explores how to integrate Redis strategically for cache warming, stampede protection, and tiered TTL strategies that balance freshness and performance. It then explains Varnish configuration options, such as BAN versus PURGE and how Drupal’s Purge module ecosystem can be used to propagate cache tags to the reverse proxy. Finally, the article discusses edge caching with Akamai, including pattern‑based and API purges, and how TTL hierarchies between the edge, proxy, and application layers work together. Real‑world metrics from a high‑traffic site demonstrate dramatic improvements in response times and cache hit rates when these layered invalidation strategies are applied.