The 5-hour CDN

Summary

The post presents a five-hour path to building a functional content delivery network as a distributed caching proxy rather than a Google-scale infrastructure project. It defines the architecture as NGINX instances deployed across cities, with DNS rules or Anycast directing users to regions and hash-based load balancing assigning URLs to cache shards. Health checks and multi-location monitoring detect failed or slow regions, while peer caches, origin-access protection, and request coalescing address redundancy, security, and cache-miss spikes. The design can improve cache ratios and reduce origin load, but cross-region proxying can add latency, and distributed invalidation remains unresolved; app-specific workloads may be better served by distributing the application itself. The conclusion is that existing NGINX features and modest scripting make a simple CDN practical, while advanced capabilities such as image optimization, WAF, rate limiting, and bot detection remain possible extensions.

Takeaways

1. 1

   Hash-based load balancing lets NGINX route the same URL to the same available cache shard, allowing servers to provide both proxying and storage.

2. 2

   Adding regional redundancy can reduce failure impact but lower cache ratios unless servers share cache responsibility through sharding.

3. 3

   Request coalescing prevents a cache miss during a traffic surge from turning into many simultaneous origin requests for the same URL.