Podcast home feed
Design the home-page recommendation system for a podcast app with 100M users and 5M shows (50M episodes). The home feed must mix continue-listening, new-episode alerts from followed shows, and discovery. Constraint: p95 under 200ms for the full feed, the catalog has heavy popularity skew, and episodes go stale fast (a daily news show episode is worthless in 48h).
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.
Clarify6:00 left
Estimate6:00 planned
Design18:30 planned
Deep dive14:30 planned
Failure10:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.