Design a Load Balancing for PlanetScale
Last updated: August 25, 2025
Quick Overview
Design a high-throughput load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PlanetScale
August 25, 2025116
15
406 solved
Design a high-throughput load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at PlanetScale typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
Key Topics to Cover
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 optimize costs as the system scales?
- What would the deployment pipeline look like for this system?
- How would you migrate from a monolithic to a microservices architecture?
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Requirements
- Functional Requirements:
- High Throughput: The load balancer must handle millions of requests per second (QPS) with minimal latency.
- Smart Routing: Implement intelligent routing b...
Capacity Estimation
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Traffic Estimates:
- Assume 1 million users generating an average of 10 requests per second each.
- Total QPS = 1,000,000 users * 10 requests/user = 10,000,000 QPS.
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Storage Needs: -...
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