System Design Interviews
System design interviews are a type of technical interview where you’re asked to design a system or part of a system, often on a whiteboard or through a virtual collaboration tool.
Unlike coding interviews that focus on specific data structures or algorithms, a System Design Interview (SDI) assesses your ability to design a complex system at a high level. You'll be given an open-ended problem, like "Design a URL Shortener (like TinyURL)" or "Design a Food Delivery App," and you'll need to architect a solution.
It's less about arriving at a single "correct" answer (there often isn't one) and more about:
- Problem Understanding & Scoping: Can you ask the right questions to clarify ambiguous requirements?
- Architectural Thinking: Can you break down a large problem into manageable components?
- Technical Trade-offs: Can you identify and articulate the pros and cons of different design choices?
- Scalability & Performance: Can you design a system that handles growth and performs efficiently?
- Reliability & Availability: Can you build in fault tolerance and ensure the system stays up?
- Communication: Can you clearly explain your thought process and justify your decisions?
Why Do Companies Even Bother with System Design Interviews?
For backend roles, especially senior ones, coding is just one part of the job. Engineers are expected to:
- Make High-Impact Decisions: Choosing the right database, caching strategy, or communication protocol can make or break a product.
- Understand the Big Picture: How do different services interact? What are the system-wide implications of a particular design?
- Lead and Mentor: Senior engineers often guide architectural discussions and mentor junior team members.
- Handle Ambiguity: Real-world problems are rarely well-defined.
- Think About the Future: Design systems that can evolve and scale.
The SDI is the best proxy companies have to evaluate these crucial skills in an interview setting.