Architect a scalable Load Balancing Engine
Last updated: December 4, 2025
Quick Overview
Design a scalable load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
MongoDB
December 4, 202550
14
559 solved
Design a scalable load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during System Design Round at MongoDB. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. MongoDB values engineers who can think about scalability from day one.
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 do you ensure data consistency across multiple services?
- How would you handle a region-wide outage?
- How would you handle a 10x increase in traffic overnight?
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Requirements
Functional Requirements
- Load Balancing: Distribute incoming requests evenly across multiple backend servers.
- Health Checks: Regularly monitor the health of backend services and rerou...
Capacity Estimation
Back-of-Envelope Calculations
- User Base: Assume 1 million concurrent users.
- Requests per User: Each user generates an average of 10 requests per minute.
- Total Requests:
- ...
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