CDN Cache Key Design That Works

Cache key design determines hit rate. The principles, the pitfalls, and the metrics that prove cache health.

Design principles

Strip query params that do not affect content. Tracking params especially.

Normalize headers: case-insensitive, sorted. Different orderings should not produce different keys.

Pitfalls

Including auth headers in cache key. Cache fragmentation; effectively no caching.

Including user-specific headers. Each user gets their own cache slot.

Metrics

Cache hit rate per route. Below 80% is suspect for static content.

Cache key cardinality. Growing without traffic growing means key design has a leak.