Design a feature store for a real-time fraud detection model.
A bank-round system design where the budget math does the screening: ~10ms for features inside a 100ms decision. Streaming aggregates, the hot-key problem during an active attack, and the parity discipline that makes training data honest.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
A bank-round system design where the budget math does the screening: ~10ms for features inside a 100ms decision. Streaming aggregates, the hot-key problem during an active attack, and the parity discipline that makes training data honest.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.