Meta Principal Engineer Mock Interview

Tell me about a time you led a cross-functional technical effort at scale (e.g., backend + infra + product) where there were strong disagreements; how did you align people, make tradeoffs, and drive the project to a successful rollout at Meta-like scale?

Meta builds systems that run globally with strict reliability and performance needs—describe a production incident you owned end-to-end. What were the signals you used, how did you narrow root cause quickly, and what changes did you implement to prevent recurrence?

Design a system for one of Meta’s graph- or feed-adjacent components (you can pick: ranking feature store, recommendation candidate generation, or identity/edge mapping). Walk through your architecture, data flow, latency/throughput targets, and how you’d evolve it safely with experimentation and backfills.

How do you approach building and guiding a “responsible engineering” culture when you’re the Principal Engineer—specifically around data privacy, content integrity, or safety risks? Share an example where you influenced product/engineering decisions to mitigate risk without blocking iteration.

Imagine you’re asked to improve a critical service’s efficiency (cost, latency, or energy) but the team is already stretched and there’s limited observability. What would you do in the first two weeks to diagnose, propose measurable improvements, and get buy-in from both engineers and product stakeholders?