Topic Guide
System Design Interview Questions
System design interviews test your ability to build large-scale distributed systems under real-world constraints. You are expected to define requirements, propose a high-level architecture, and dive into specific components such as databases, caches, load balancers, and message queues. These questions appear at every major tech company and are weighted heavily for senior and staff-level roles.
0Questions
177Companies
5Roles
All System Design Interview Questions
View all system design interview questionsFilter by:
Loading questions...
Frequently Asked Questions
What is the difference between horizontal and vertical scaling?
Horizontal scaling adds more machines to your pool (scale out), while vertical scaling adds more power to an existing machine (scale up). Horizontal scaling is preferred for distributed systems because it avoids single points of failure and allows near-linear throughput growth, but adds complexity around data consistency and load distribution.
How do you approach a system design interview question?
Start by clarifying requirements and constraints. Estimate the scale (users, QPS, storage). Propose a high-level architecture with major components. Then deep-dive into specific areas like the database schema, caching strategy, or API design. Discuss trade-offs explicitly and address failure scenarios.
When should you use a SQL vs NoSQL database?
Use SQL when you need ACID transactions, complex joins, or structured data with well-defined schemas. Use NoSQL for high write throughput, flexible schemas, horizontal scaling, or when your access patterns are simple key-value or document lookups.
What is a load balancer and why is it needed?
A load balancer distributes incoming traffic across multiple servers to prevent any single server from becoming a bottleneck. It improves availability, enables horizontal scaling, and can route requests based on various algorithms like round-robin, least connections, or consistent hashing.
What Interviewers Look For
Interviewers evaluate your ability to make principled trade-offs between consistency, availability, latency, and cost. They want to see structured thinking, clear communication, and awareness of failure modes. Strong candidates scope the problem, estimate scale, and justify each design choice.