CDN and edge caching: accelerating global content delivery

Content Delivery Networks are the backbone of fast global web experiences. A CDN caches your content at edge locations worldwide, serving users from the nearest server. Proper CDN configuration reduces latency, offloads origin traffic, and improves availability.

Cache strategy depends on content type. Static assets like images, CSS, and JavaScript can be cached aggressively with long TTLs. API responses can be cached with shorter TTLs or validated with ETags. HTML pages can be cached with CDN or in a layered approach.

Cache invalidation is the hardest part of CDN caching. Use cache tags or surrogate keys to selectively purge content when it changes. Most CDNs support tag-based invalidation: when a product price changes, purge all pages with the "product-123" tag. This is more precise than purging entire URL patterns.

Stale-while-revalidate serves stale content immediately while fetching fresh content in the background. This eliminates the latency of a cache miss. Users see fast responses, and the cache is always eventually fresh. Configure this for content where slight staleness is acceptable.

Custom origin configuration matters. Set appropriate Cache-Control headers from your origin. Use compression to reduce transfer size. Configure keep-alive connections. Monitor origin response times a slow origin negates the benefit of a fast CDN.

Security features at the CDN layer include DDoS protection, WAF rules, and bot management. Enable HTTPS with automated certificate management. Configure security headers at the edge. Use rate limiting at the edge to protect your origin from traffic spikes.

Monitor CDN performance with cache hit ratio, origin offload percentage, and edge response times. A cache hit ratio below 70% suggests your caching strategy needs improvement. Set up alerts for sudden drops in cache hit ratio, which may indicate a configuration issue.

-

Rizwan Saleem | https://rizwansaleem.co