System design interview question
Design an IoT Data Platform
An IoT data platform onboards millions of constrained devices, ingests their telemetry over MQTT, runs edge filtering to keep cloud costs sane, stores time-series data efficiently for years, maintains a queryable "shadow" state for each device, sends commands back to devices, manages firmware over-the-air, and detects anomalies in near real time. The design must work with intermittent connectivity (a sensor on a wind turbine may go offline for hours), constrained device memory (some have only 64 KB RAM), and security at scale (each device has unique credentials and can only access its own resources).
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