Design access control and heartbeat systems
Company: Verkada
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Design two backend systems.
**Part A: Door access control system**
Design a service that manages which people can open which doors. The system must support:
- Given a person ID, list all doors that person can open.
- Given a door ID, list all people who can open that door.
- As an administrator, grant a person access to a door.
Discuss the data model, API design, indexing strategy, authorization rules, and how you would handle auditability and future operations such as revoking access.
**Part B: Device heartbeat monitoring system**
Design a simple system for **10 million devices**, where each device sends a heartbeat **once per minute**. Build a dashboard that shows device health and online status.
Discuss:
- Expected write throughput
- Ingestion architecture
- Storage design for recent status and historical heartbeats
- How to determine whether a device is online or offline
- Dashboard APIs and useful metrics
- Reliability, scaling, and failure handling
Quick Answer: This question evaluates a candidate's ability to design backend systems covering access control data modeling, APIs, authorization and auditability, alongside high-scale telemetry ingestion, storage, and monitoring for device heartbeats.