API Gateway — Part 4: Staff/Principal-Level Interview Q&A

What is this?

You've learned the machinery across Parts 1–3. This chapter is the dress rehearsal — me playing interviewer, you in the hot seat. The questions below are the ones that actually come up at Staff and Principal level, where nobody cares that you can define "API gateway" and everybody cares whether you understand its consequences and trade-offs.

For each one I'll show you what they're really asking (the hidden agenda behind the question), a model answer you can adapt, and the senior line — the single sentence that signals you've operated this in production, not just read about it.

The one-line idea: at this level, the gateway questions aren't about features — they're about trade-offs, failure modes, and knowing where the gateway ends. Answer the question behind the question.