System Design Questions: An Interviewee’s Ultimate Checklist

System design interviews can feel like navigating a maze without a map. I remember when I first started facing these interviews, I was often overwhelmed by the sheer scope of what was expected. I'd either focus too much on the technical details or miss crucial requirements entirely. Over time, I realised that approaching these interviews with a structured checklist can make all the difference.

So, if you're prepping for your next system design interview and want to ensure you've covered all bases, you're in the right place. Let's dive into the ultimate checklist that can help you approach these interviews with confidence.

1. Clarify Requirements

What are the functional requirements? List every feature the system needs to support. Don't assume anything; ask questions. For instance, in a ride-sharing app, is real-time tracking a must-have, or a nice-to-have?
What are the non-functional requirements? Think about scalability, reliability, latency, and security. How many users do you expect? What's the acceptable response time? What level of fault tolerance is needed?
What are the constraints? Are there any limitations on budget, technology, or team size? Understanding these constraints upfront can help you make realistic design decisions.

2. High-Level Design (HLD)

Sketch out the major components of the system. Identify the key services, databases, and external APIs. Draw a simple block diagram to visualise the architecture. This provides a bird's-eye view of the system.
Define the data flow. How does data move between components? What protocols are used? What data formats are involved? Understanding the data flow helps identify potential bottlenecks.
Address scalability concerns. How will the system handle increased load? Will you use load balancers, caching, or auto-scaling? Discuss different scaling strategies and their trade-offs.

3. Database Design

Choose the right database. Will you use a relational database (SQL) or a NoSQL database? Consider factors like data consistency, scalability, and query patterns. For example, a social network might benefit from a graph database for relationship management.
Design the schema. Define the tables, columns, and relationships. Consider normalisation and indexing for performance. A well-designed schema can significantly improve query performance.
Think about data partitioning. How will you distribute data across multiple servers? Consider techniques like sharding, replication, and consistent hashing. Data partitioning is crucial for handling large datasets.

4. Caching Strategy

Identify caching opportunities. What data is frequently accessed and rarely changes? These are prime candidates for caching. For instance, user profiles or product catalogs.
Choose a caching mechanism. Will you use in-memory caching (e.g., Redis, Memcached) or a content delivery network (CDN)? Consider factors like cache invalidation and cache eviction policies.
Consider cache coherence. How will you ensure that the cache remains consistent with the underlying data? Discuss strategies like write-through, write-back, and cache invalidation.

5. API Design

Define API endpoints. What are the key operations that the system needs to expose? Use RESTful principles for designing your APIs. For example, /users/{id} for retrieving user information.
Consider API rate limiting. How will you prevent abuse and ensure fair usage? Implement rate limiting to protect your system from excessive requests. This is especially important for public APIs.
Think about API versioning. How will you handle changes to the API over time? Use versioning to maintain backward compatibility. For instance, /v1/users/{id} and /v2/users/{id}.

6. Scalability and Availability

Discuss horizontal vs. vertical scaling. When is it appropriate to add more machines (horizontal scaling) versus upgrading existing machines (vertical scaling)? Horizontal scaling is generally preferred for cloud-based systems.
Implement load balancing. How will you distribute traffic across multiple servers? Use load balancers to ensure that no single server is overwhelmed. Consider different load balancing algorithms.
Ensure fault tolerance. How will the system handle failures? Implement redundancy and failover mechanisms. For example, using multiple availability zones in a cloud environment.

7. Security Considerations

Implement authentication and authorisation. How will you verify the identity of users and control access to resources? Use industry-standard protocols like OAuth and JWT. Security should be a primary concern.
Protect against common attacks. How will you prevent SQL injection, cross-site scripting (XSS), and other common attacks? Use input validation, output encoding, and other security measures.
Consider data encryption. How will you protect sensitive data at rest and in transit? Use encryption algorithms like AES and TLS. Data encryption is crucial for maintaining data privacy.

8. Monitoring and Logging

Implement monitoring tools. How will you track the health and performance of the system? Use tools like Prometheus, Grafana, and ELK stack. Monitoring is essential for identifying and resolving issues.
Implement logging. What events will you log? Use structured logging to make it easier to analyse logs. Logging is crucial for debugging and auditing.
Set up alerts. How will you be notified of critical issues? Configure alerts to notify you when certain thresholds are exceeded. Alerts help you respond quickly to problems.

9. Communication and Trade-offs

Communicate clearly. Explain your design decisions and reasoning. Use diagrams to illustrate your ideas. Effective communication is key to a successful interview.
Discuss trade-offs. Every design decision involves trade-offs. Be prepared to discuss the pros and cons of different approaches. Show that you understand the implications of your choices.
Listen to feedback. Be open to suggestions and criticisms. Show that you are willing to learn and adapt. Listening to feedback demonstrates your ability to collaborate.

10. Practice, Practice, Practice

Solve real-world problems. Work through system design problems on platforms like Coudo AI. Apply your knowledge to practical scenarios. Practice makes perfect.
Review case studies. Study the architectures of popular systems like Netflix, Uber, and Twitter. Learn from their design decisions and challenges. Case studies provide valuable insights.
Get feedback. Ask friends or colleagues to conduct mock interviews. Get feedback on your design approach and communication skills. Feedback helps you identify areas for improvement.

FAQs

Q1: How much detail should I go into during a system design interview?
Aim for a balance.
Provide enough detail to demonstrate your understanding, but don't get bogged down in unnecessary complexity.
Focus on the key design decisions and trade-offs.

Q2: What if I don't know the answer to a question?
Be honest.
It's better to admit that you don't know something than to try to bluff your way through it.
Explain your thought process and how you would approach finding the answer.

Q3: How important is coding in a system design interview?
Coding is usually not the primary focus, but it can be helpful to illustrate certain concepts.
Be prepared to write some code snippets to demonstrate your understanding of algorithms, data structures, and concurrency.

Wrapping Up

I hope this ultimate checklist helps you approach your next system design interview with confidence. Remember, preparation is key. By systematically covering each aspect of system design, you can showcase your expertise and impress your interviewer. For more practice and real-world problems, check out Coudo AI. Good luck, and keep designing amazing systems! The key to system design interview success lies in thorough preparation and a structured approach.