Design a Load Balancing Service
Last updated: September 2, 2025
Quick Overview
Design a geo-distributed load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Doordash
System Design
Software Engineer
Doordash
September 2, 2025Software Engineer
Onsite
System Design
Medium
1
14
2,013 solved
Design a geo-distributed load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Doordash 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
- 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
Partitioning and sharding strategies
Message queues and async processing
Failure handling and fault tolerance
Requirements gathering and capacity estimation
Database selection and data modeling
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 implement rate limiting to protect the system?
- How would you migrate from a monolithic to a microservices architecture?
- How would you handle a region-wide outage?
- How do you ensure data consistency across multiple services?
Practice a Similar Problem on Codemia
Solve a related problem with our interactive workspace, get AI feedback, and view detailed solutions.
Solve on CodemiaSample Answer
Requirements
Functional Requirements:
- Request Routing: The system must intelligently route millions of incoming requests from users to the nearest or least-loaded service instance based on geographical ...
Capacity Estimation
Capacity Estimation:
- User Base: Assume 10 million active users on the platform.
- Requests per User: Estimate an average of 5 requests per user per day, leading to a total of 50 million ...
Submit Your Answer
Markdown supported