System designMediumsd-g527

Subject Pub subLevel Mid–Senior~45 minCommon in Distributed systems interviewsIndustries Technology, Telecom, Software development

Question

Design the cloud ingestion and command pub-sub layer for an IoT fleet: 20M devices on constrained networks (intermittent cellular, low bandwidth, sleepy devices) publishing telemetry and subscribing to commands. Requirements: efficient on the wire, support at-most-once/at-least-once delivery levels, deliver commands to devices that were offline when the command was issued, and authenticate per-device. Bursts when a firmware push wakes the whole fleet.

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.