Cache Consistency and Purging Across CDNs
Synopsis This chapter explains how to keep caches consistent when more than one CDN serves the same content. It covers cache key design, HTTP caching headers, immutable assets, purge methods, sequencing across providers, and the operational controls that keep correctness and latency predictable. Purpose and scope Multi-CDN changes cache behavior because different networks fetch, store, and expire objects using different rules and clocks. The goal is that users receive the same bytes for the same URL regardless of the serving CDN and that changes reach users in a controlled and explainable way. The guidance applies to static assets and dynamic responses that allow caching. It also covers the surrounding systems that push and purge content. ...