Leader election for stream partitions
Design leader election for a sharded stream-processing system where each of 4,000 partitions must have exactly one active processor writing to a downstream sink. Processors run on autoscaled, preemptible VMs that can pause (GC, network partition) for tens of seconds. A second processor must never write the same partition's output concurrently, even if the 'old' leader is merely slow and not dead. How do you elect leaders and guarantee single-writer at the sink?
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.