Design a Monitoring Service
Last updated: October 5, 2025
Quick Overview
Design a high-throughput monitoring system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PlanetScale
System Design
Software Engineer
PlanetScale
October 5, 2025Software Engineer
Onsite
System Design
Easy
0
10
2,667 solved
Design a high-throughput monitoring system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PlanetScale asks this during the Onsite to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
What the Interviewer Expects
- Clearly define functional and non-functional requirements
- Propose a reasonable high-level architecture with core components
- Choose appropriate data storage solutions with basic justification
- Discuss basic scaling strategies (horizontal scaling, caching)
- Identify potential bottlenecks and suggest simple solutions
Key Topics to Cover
API design and rate limiting
Monitoring, logging, and alerting
Message queues and async processing
Database selection and data modeling
Load balancing and horizontal scaling
Caching strategies (local, distributed, CDN)
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle schema migrations with zero downtime?
- How do you ensure data consistency across multiple services?
- What monitoring and alerting would you set up on day one?
- How would you handle a region-wide outage?
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Requirements
- Functional Requirements:
- Ability to ingest monitoring data from millions of sources in real-time.
- Provide a REST API for clients to submit metrics and logs.
- Support querying monitori...
Capacity Estimation
- Assuming each client sends 1 metric per second on average.
- For 1 million clients, this results in:
- 1 million metrics per second.
- If we anticipate 10% of clients sending logs at the same ...
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