System design interviews can be intimidating, especially when you're faced with an open-ended problem and a blank whiteboard. However, having a structured framework to approach these problems can dramatically improve your performance. In this article, I'll share a proven framework that has helped countless engineers succeed in system design interviews at top tech companies.
1. Requirements (~5 minutes)
Start by clearly defining the scope of the problem. This shows the interviewer that you don't jump into solutions without understanding the problem first.
Functional Requirements
These are the core features your system needs to support. For example, if designing a video streaming service:
- Users should be able to upload videos
- Users should be able to watch videos at different quality settings
- Users should be able to search for videos
- Users should be able to like, comment, and share videos
Non-functional Requirements
These describe the qualities of your system:
- Scalability: How many users does the system need to support? What's the expected growth?
- Availability: What's the expected uptime? Can the system tolerate downtime?
- Consistency vs. Availability: Which is more important for your use case? (CAP theorem consideration)
- Latency: What are acceptable response times for various operations?
- Durability: How critical is it that data is never lost?
- Security and Privacy: What level of protection does the data require?
Capacity Estimation
Make reasonable assumptions to estimate:
- Number of daily active users (DAU)
- Requests per second
- Storage requirements (GB/TB)
- Bandwidth usage
2. Core Data Entities (2-3 minutes)
Define the main objects in your system and their relationships:
- What are the primary entities (e.g., User, Video, Comment)?
- What attributes do these entities have?
- How do these entities relate to each other?
This step forces you to think about data modeling early, which influences your API design and storage decisions.
3. API Design (5 minutes)
Outline the key endpoints your system will expose:
POST /api/videos
Request: { title, description, videoFile }
Response: { videoId, processingStatus }
GET /api/videos/:videoId
Response: { videoId, title, url, stats }
POST /api/videos/:videoId/comments
Request: { text }
Response: { commentId, timestamp }
This step shows your ability to create clean interfaces and think from a client perspective.
4. High-Level Architecture (10-15 minutes)
This is where you sketch the major components of your system:
- Front-end clients: Web, mobile, smart TVs
- API Gateway/Load Balancer: Entry point for requests
- Application servers: Business logic processing
- Databases: Data persistence (SQL vs. NoSQL considerations)
- Caching layer: Improving read performance
- CDN: Content delivery for static assets
- Message queues: For asynchronous processing
- Storage systems: For user-generated content
Draw boxes and arrows to show how data flows through the system. Discuss trade-offs of different architectural choices.
5. Deep Dives (10 minutes)
Based on interviewer's feedback, explore specific components in detail:
- Scaling strategies: Horizontal vs. vertical scaling
- Database design: Schema design, sharding strategies
- Caching strategies: Cache invalidation, eviction policies
- Content delivery: How to efficiently serve video content globally
- Failure handling: Redundancy, failover mechanisms
- Real-time features: WebSockets, push notifications
- Analytics and monitoring: How to track system health
Common Pitfalls to Avoid
- Rushing to code: System design is about architecture, not implementation details
- Neglecting requirements clarification: Always verify assumptions
- Ignoring scalability: Your solution must work at scale
- Going too deep too early: Start broad, then narrow down
- Being vague about trade-offs: Explicitly state pros and cons of your decisions
Final Tips
- Practice drawing diagrams - clarity is crucial
- Use real-world examples to demonstrate your experience
- Listen carefully to the interviewer's hints
- Be adaptable - be ready to pivot your approach based on feedback
- Think out loud - interviewers want to understand your thought process
Remember, system design interviews assess your ability to build scalable, robust systems. They're less about finding a single correct answer and more about demonstrating your problem-solving approach, technical knowledge, and communication skills. With proper preparation and a structured framework, you can tackle even the most challenging system design questions with confidence.
Happy designing!