Senior interview questionAsked at Reddit · interview write-up
Design a video recommendation system for the home feed and up-next, focusing on infrastructure, logging and observability.
Model answer
One stack, two contexts: home feed has no seed; up-next adds the current video. Candidates come from ANN over video embeddings, co-watch, subscribed communities and trending, then a GPU ranker reads the online feature store.
Logging is the backbone: every impression records request ID, model version, candidates, scores, position and features as served. Client events like watch seconds and skips join by request ID into skew-free training data.
Observability: per-stage latency SLOs, candidate counts per source, empty results, feature freshness, score and calibration drift, and per-surface business metrics. Ship via canary with automatic rollback.
Practise the rest
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