How do HTTP caching and CDNs improve performance?
Assesses fundamental understanding of Web Performance conventions, runtime behavior, and memory/performance considerations.
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Caching avoids re-downloading assets and is one of the cheapest performance wins. Use content-hashed filenames with a long Cache-Control: public, max-age=31536000, immutable for static assets, so repeat visits hit the browser cache. HTML should be short-lived and revalidated with no-cache or a small max-age so deployments are picked up. ETag with If-None-Match and Last-Modified with If-Modified-Since enable conditional requests that return 304 instead of a body. stale-while-revalidate and stale-if-error let a CDN serve slightly stale content while refreshing in the background, improving availability.
CDNs cache at edge locations close to users, reducing TTFB and offloading origin traffic. Configure s-maxage and Vary carefully, because Vary fragments caches, and purge on deploy.
A service worker adds a client-side layer for offline use and instant repeat loads, but cache invalidation must be handled carefully or users get stuck on old versions. Always verify headers in the network panel.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.