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Caching Strategies for Web Apps: CDN, Redis, Browser, and API Caching

Caching is the difference between a 50ms response and a 5-second timeout. But cache invalidation is famously one of the hardest problems in computer science. Here's a practical guide to caching at every layer — and when NOT to cache.

The Caching Layers

Layer What to Cache TTL Invalidation

Browser (HTTP Cache) Static assets (JS, CSS, images, fonts) 1 year (with hash in filename) Change filename → new URL → cache miss

CDN HTML, API responses, images 1 min to 1 hour Purge by URL or tag. Stale-while-revalidate.

Application (Redis/Memcached) DB query results, computed values, sessions 1 second to 1 hour Delete on write. TTL-based.…