L4
L4 — Software Engineer II (correctness of one component)
At L4, the interviewer wants to see that you can correctly design one non-trivial component end-to-end. Depth beats breadth. You are not expected to design a globally distributed system.
Day-to-day responsibilities
- Implement well-scoped features on an established service
- Choose data structures and APIs correctly at your component boundary
- Understand and reason about a single database, cache, or queue
- Debug your service in production with guidance
Interview signals
- Clear, testable API for the chosen component
- Correct data model with reasonable indexing choices
- Awareness of at least one caching strategy
- One realistic failure scenario reasoned about
Problem focus
- URL shortener, pastebin, notification service, rate limiter
- Prefer a single-region, single-database design
Delivery advice
- Don't jump to microservices; a monolith is often the right answer at this level
- Show correctness before scale — a slow, correct answer beats a fast, wrong one
- Talk about the boundary of your component and where responsibilities stop