api-caching

API performance optimization with HTTP caching headers involves configuring `Cache-Control`, `ETag`, `Last-Modified`, and `Vary` to manage client and CDN caching effectively. This reduces server load and improves response times by enabling conditional requests.

CDN cache invalidation is best handled using surrogate keys or path purging to ensure timely cache updates. Surrogate keys allow targeted invalidation of specific content groups when underlying API data changes, avoiding full cache flushes.

Redis application-level caching provides granular data caching and invalidation at the server level, whereas HTTP caching uses headers like `Cache-Control` for client and CDN caching. Redis is ideal for caching database queries or complex computations.

Vary headers are needed for API caching when responses differ based on request headers like `Accept-Encoding` or `Authorization`. Adding `Vary` ensures CDNs and clients cache distinct representations correctly, preventing serving wrong content variants.

Yes, you can use `stale-while-revalidate` for near-instant API responses by allowing caches to serve stale content while fetching a fresh copy in the background. This strategy drastically reduces latency for users while maintaining data freshness.