How does CloudFront (CDN) improve performance, and what do you cache vs not?
Reviewed by Gurusankar M.
⚡ Short Answer
CloudFront caches content at edge locations near users, cutting latency and offloading origin traffic. Cache static assets aggressively (long TTL + cache-busting filenames); use short/no cache for dynamic/personalized responses. Control behavior with cache policies (TTLs, which headers/cookies/query strings form the cache key).
☕Coffee Chat Question
Concept Made Simple
“How does CloudFront (CDN) improve performance, and what do you cache vs not?”
🧠Mind Map Answer
Remember It Faster
🔥What If?
Think Beyond the Expected
Users see stale content after a deploy — how do you avoid it without manual invalidations?
Use content-hashed filenames (app.a1b2c3.js) so each deploy produces new URLs the CDN treats as new objects — old cached files just age out. This 'cache-busting' avoids costly/global invalidations and eliminates stale-asset bugs.
😂Real World
CDN in front of S3/ALB with hashed asset filenames is standard for web performance; relying on manual invalidations instead of cache-busting is a common source of stale-content incidents.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗Caching personalized/dynamic responses
- ✗Relying on manual invalidations
- ✗Cache key including too many varying headers (low hit rate)
✅Best Practices
- ✓Cache-bust static assets with hashed names
- ✓Short/no cache for dynamic content
- ✓Tune the cache key for a high hit rate
🔁Follow-up Questions
- 1How does the cache key affect hit rate?
- 2When do you invalidate vs version?
- 3Origin Access Control for private S3 origins?
🧩Related Technologies
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Plain-language foundations
I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner. Topic: S3 (AWS) Interview question: "How does CloudFront (CDN) improve performance, and what do you cache vs not?" Please: 1. Explain the core idea in simple, plain language, using an everyday analogy. 2. Define any technical terms you use. 3. Walk through one small, concrete example. 4. Finish with a single sentence I can easily remember. Keep the tone friendly and assume I'm new to this topic.
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