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Interview Question
A misconfigured deployment invalidates most CDN cache objects at once, flooding the origin. What’s your triage and prevention plan?
Key Points to Cover
- Throttle/queue invalidations and pause non-critical purges
- Enable stale-while-revalidate and serve-stale-on-error
- Raise origin capacity or enable origin shield/tiers temporarily
- Fix cache keys/headers to limit unnecessary purges
- Add guardrails and change reviews for invalidation jobs
Evaluation Rubric
Stabilizes CDN and origin quickly30% weight
Uses correct caching semantics30% weight
Manages origin capacity/shielding20% weight
Prevents future storms via guardrails20% weight
Hints
- 💡Invalidations should be scoped by path/prefix.
Common Pitfalls to Avoid
- ⚠️Failing to immediately pause invalidations, exacerbating the problem.
- ⚠️Not having a clear rollback or correction plan for the misconfiguration.
- ⚠️Overlooking 'stale-while-revalidate' or similar caching strategies as a quick fix.
- ⚠️Underestimating the time and resources needed to scale origin capacity.
- ⚠️Skipping the post-mortem analysis and failing to implement preventative measures.
Potential Follow-up Questions
- ❓What KPIs show healthy cache behavior?
- ❓How to test invalidations safely?
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