Durable append-only log
Design a durable append-only / write-ahead-log store that other services use as their commit log (think a Kafka/BookKeeper-style log). Constraints: writes must be durable before ack (no data loss on a single-node power failure), ordered within a partition, high append throughput (hundreds of MB/s per partition), readers tail the log with low latency, and you replicate for fault tolerance. Cover the append path, durability guarantee, and replication.
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.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 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.