Design a CDN Edge Caching Strategy

To design an effective CDN edge caching strategy, I first categorize content types because a one-size-fits-all approach fails at scale. For static assets like CSS or images, I would implement aggressive Time-To-Live (TTL) values, perhaps days or weeks, relying on URL fingerprinting for cache busting when updates occur. This drastically reduces origin load. However, for dynamic content, I'd use shorter TTLs combined with Cache-Control headers like 'no-cache' for personalized user data to prevent serving stale information. Regarding cache key granularity, it is critical to include specific request headers like 'Accept-Language' or 'X-Geo-Region'. Without this, a user in Tokyo might receive cached content intended for New York, leading to poor localization experiences. At Amazon, where global scale is paramount, we must also consider cache invalidation. Instead of manual purges which are slow, I prefer tag-based invalidation or event-driven triggers from the origin service to propagate changes instantly across edge nodes globally. Finally, I would monitor the cache hit ratio and error rates per region. If a specific region shows low hits, it indicates a potential configuration issue with our regional edge nodes or incorrect key generation, allowing us to tune the strategy dynamically.