What does a CDN cache and how does it help?
Assesses fundamental understanding of Caching Strategies 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.
A content delivery network caches content on edge servers close to users. It serves static assets such as images, CSS, JavaScript and fonts, and can cache dynamic responses and API responses when headers permit.
Benefits: lower latency from geographic proximity, offloaded origin traffic, absorption of traffic spikes and DDoS mitigation, plus TLS termination at the edge.
Cache-Control: public, max-age=31536000, immutable
Cache-Control: s-maxage=60, stale-while-revalidate=30
Control behavior with Cache-Control (max-age for browsers, s-maxage for shared caches, private, no-store), ETag for revalidation, and Vary to prevent serving one user's response to another. Invalidate by purging URLs or using surrogate keys. A crucial warning: never cache authenticated or personalized responses in a shared cache unless the cache key includes the identity, or you will leak data across users.
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.