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Design power grid device monitoring over an unreliable public internet

OpenAISoftware Engineer · Onsite
MediumSoftware EngineerOnsiteSystem Design

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Design a monitoring system for power grid field devices that report their status over an unreliable public internet. It tests store-and-forward reporting, idempotent ingestion of late and duplicate data, telling silent devices from failed ones, alerting, and security for critical infrastructure.

Design a system that monitors devices on a power grid. Devices in the field report their status to a central monitoring system over the public internet, and the public internet is unreliable: connections drop, messages are delayed or repeated, and a device can stay unreachable for long periods. Operators use the system to see the current state of the grid and to be alerted when something goes wrong.

Clarifying Questions

  • How many devices are there, how often does each one report, and what does a status report contain?
  • Is the system for monitoring only, or must it also send commands back to devices?
  • How quickly must an operator learn that a device has failed or gone silent?
  • How much storage and compute do the devices have for buffering?
  • How long must status history be kept, and at what resolution?

Hints

Hint 1

Silence is ambiguous: When a device stops reporting, list everything that could explain it, and what the system would need to tell those cases apart.

Hint 2

Where data can be lost: Trace one status report from the device to the operator's screen, and mark every point where it can be dropped, duplicated or delayed.

Follow-up questions

  • A regional internet outage takes many devices offline for an hour, and then they all reconnect at once. Walk through what your system does, step by step.
  • If operators must also send commands to devices, what changes in the protocol, the architecture and the safety requirements?
  • How would you detect a device that keeps reporting on schedule but whose readings are wrong?