Technical Interview Preparation: System Design Questions

Why System Design Matters in 2025

According to Levels.fyi, system design interviews are now required for all L5+ roles at major tech companies. These interviews assess your ability to think at scale, make architectural decisions, and communicate complex ideas. With AI tools like GPT-4 able to solve many coding problems, companies are placing even more emphasis on system design to evaluate senior candidates.

The System Design Framework

Use this structured approach for any system design question:

Step 1: Clarify Requirements (5 minutes)

Before designing anything, understand the scope:

• What are the core features we need to support?
• What is the expected scale (users, data, requests)?
• What are the latency requirements?
• Do we need to prioritize consistency or availability?
• Are there any specific constraints or limitations?

Step 2: Estimate Scale (5 minutes)

Do back-of-envelope calculations:

• Daily Active Users (DAU)
• Requests per second (read vs write ratio)
• Data storage requirements
• Bandwidth needs
• Memory/cache requirements

Step 3: High-Level Design (10 minutes)

Draw the major components:

• Client applications
• Load balancers
• Web servers
• Application servers
• Databases (SQL vs NoSQL)
• Caching layer
• CDN for static content

Step 4: Deep Dive (15 minutes)

Choose 2-3 components to explore in detail:

• Database schema design
• API design
• Data partitioning strategy
• Caching strategy
• Specific algorithms or data structures

Step 5: Address Bottlenecks (5 minutes)

Identify and solve potential issues:

• Single points of failure
• Hot spots in data distribution
• Scalability limitations
• Security considerations
• Monitoring and alerting

Common System Design Questions

• Design a URL shortener (like bit.ly)
• Design a social media feed (like Twitter)
• Design a chat application (like WhatsApp)
• Design a video streaming service (like YouTube)
• Design an e-commerce platform (like Amazon)
• Design a search engine (like Google)

Key Concepts to Master

• CAP Theorem: Consistency, Availability, Partition Tolerance
• Database Sharding: Horizontal partitioning strategies
• Caching: Write-through, write-back, cache invalidation
• Load Balancing: Round robin, least connections, IP hash
• Microservices: Service decomposition and communication
• Message Queues: Async processing and decoupling

Practice Resources

• System Design Primer on GitHub
• Designing Data-Intensive Applications (book)
• YouTube channels: System Design Interview, Gaurav Sen
• Practice with peers using mock interview platforms

Conclusion

System design interviews reward structured thinking and clear communication. By following a consistent framework and practicing regularly, you can confidently tackle any design challenge thrown your way.