Tamper-evident audit log
Design a tamper-evident audit-log system for a financial platform that must record every privileged action (admin logins, permission changes, money movements) such that no one — not even a DBA or a compromised insider with write access — can silently alter or delete a past entry. It ingests ~80k events/sec, must support compliance queries over years of history, and must let an auditor cryptographically prove the log has not been tampered with. Cover the append-only structure, the integrity mechanism, and how you detect deletion vs. modification.
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.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 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.