Q1
Design a distributed caching layer for a microservices architecture serving 10 million daily active users. Walk through your trade-offs between consistency, availability, and partition tolerance.
Why they ask this:* They're evaluating your ability to architect scalable systems, understand CAP theorem implications, and make informed technology decisions at the infrastructure level expected of a senior engineer.
Q2
Explain your approach to optimizing a critical service that's consuming 60% of your database query budget. What profiling tools would you use, and how would you identify whether the issue is N+1 queries, missing indexes, or inefficient joins?
Why they ask this:* They're assessing your systematic debugging methodology, familiarity with production monitoring tools, and ability to diagnose performance bottlenecks—essential skills for owning critical systems.
Q3
Describe a significant refactoring you've led to improve code maintainability or reduce technical debt. How did you balance shipping new features with paying down debt, and how did you measure success?
Why they ask this:* They want to understand your experience managing technical debt, your ability to communicate trade-offs to stakeholders, and whether you can execute complex refactoring while maintaining product velocity.
Q4
Walk me through how you would design an API contract and versioning strategy for a service consumed by 15 internal teams. How would you handle backward compatibility and migration of deprecated endpoints?