Code Room
System designHardsd-g160
Subject Anomaly detectionLevel Senior–Staff~45 minCommon in Distributed systems interviewsIndustries Technology

Question

Design an automated anomaly-detection service that watches ~500,000 production metrics in near-real-time and raises alerts without engineers hand-tuning static thresholds. Metrics have strong daily and weekly seasonality (traffic is 5x higher at noon and on weekdays). The system must detect a real regression within ~2 minutes, keep false-positive rate low enough that on-call trusts it, and scale to evaluate all series on a rolling basis. Design the modeling, the streaming evaluation, and how you control false positives.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Narrate your design
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Run or narrate your approach, then ask the coach.