Design Load Balancing Infrastructure for microservices
Last updated: January 23, 2026
Quick Overview
Design a high-throughput load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Plaid
System Design
Software Engineer
Plaid
January 23, 2026Software Engineer
System Design Round
System Design
Medium
111
7
2,900 solved
Design a high-throughput load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Plaid asks this during the System Design Round 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
- 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
Monitoring, logging, and alerting
Load balancing and horizontal scaling
Partitioning and sharding strategies
API design and rate limiting
Failure handling and fault tolerance
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 implement rate limiting to protect the system?
- How would you handle schema migrations with zero downtime?
- How would you optimize costs as the system scales?
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Requirements
Functional Requirements
- Traffic Distribution: The system must distribute incoming requests to multiple microservice instances based on predefined algorithms (round-robin, least connections,...
Capacity Estimation
Back-of-Envelope Calculations
- QPS: Assume Plaid experiences peak load of 50 million requests per day, translating to approximately:
- QPS = 50,000,000 requests/day / 86,400 seconds/day ≈...
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