Design a daily pipeline that survives reruns, late-arriving data, and a 3-year backfill, without double-counting.
The pipeline-design question that exposes whether you've ever been paged. One property, idempotency, solves reruns, late data, and backfills at once, and there are exactly three patterns that deliver it.
Updated Sep 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
The pipeline-design question that exposes whether you've ever been paged. One property, idempotency, solves reruns, late data, and backfills at once, and there are exactly three patterns that deliver it.
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.
