Explain CDN Cache Key and URL Normalization.

A CDN cache key is the unique identifier a CDN uses to store and retrieve cached content, and URL normalization ensures different URL variations pointing to the same resource map to the same cache entry.

When to Use

Use CDN cache keys to speed up delivery of static and dynamic content while reducing origin load. Apply URL normalization when multiple URL formats (e.g., query params, case differences) should resolve to the same cached asset.

Example

If example.com/product?id=123&ref=twitter and example.com/product?id=123 serve the same page, URL normalization prevents duplicate cache entries by ignoring irrelevant parameters.

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Why Is It Important

A well-defined cache key and normalized URL structure improve cache hit ratio, lower latency, and prevent wasted resources on duplicate entries. This directly enhances system scalability and user experience.

Interview Tips

Explain what a cache key is, why normalization matters, and provide an example. Highlight the trade-off between higher cache hit ratios and content correctness. Use terms like cache efficiency and origin offload to sound structured.

Trade-offs

Simpler cache keys maximize hits but risk serving incorrect content.

Complex keys ensure accuracy but reduce cache efficiency. The balance depends on business needs.

Pitfalls

Avoid including user-specific tokens (e.g., session IDs) in cache keys. Don’t over-normalize—ignoring parameters that actually change content can cause stale or wrong responses.