Do we need to code in a system design interview?

No, you typically do not need to code in a system design interview. These interviews focus on your ability to design scalable, efficient, and reliable systems, rather than your coding skills.

The goal is to assess your understanding of system architecture, decision-making, and trade-offs while solving real-world problems.

What Is Expected in a System Design Interview

1. Design High-Level Architecture

You’ll be asked to design the overall structure of a system. This includes:

• APIs: How the frontend communicates with the backend.
• Databases: Choosing SQL or NoSQL, and planning for partitioning or replication.
• Caching: Where to use it to reduce latency and improve performance.
• Load Balancing: Distributing traffic to avoid bottlenecks.
• Microservices: Designing independent, scalable services if needed.

For example, designing a system like Twitter may involve:

• Generating user timelines with caching and database optimization.
• Managing scalability to handle millions of active users.
• Implementing sharding for data partitioning.

2. Discuss Trade-offs

You must demonstrate your ability to evaluate and justify design decisions. For example:

• SQL vs. NoSQL: Choosing based on scalability, consistency, and data structure.
• Consistency vs. Availability: Prioritizing based on system requirements (e.g., banking vs. social media).
• Monolithic vs. Microservices: Balancing simplicity and scalability.

3. Handle Scalability and Fault Tolerance

You’ll explain how your system can handle growth and failures:

• Scalability: Use horizontal scaling, replication, and caching.
• Fault Tolerance: Design for redundancy, failover mechanisms, and recovery plans.

4. Use Visual Diagrams

You’ll typically draw a diagram to illustrate system components and their interactions. Key elements include:

• Clients: The users or systems interacting with your design.
• APIs: Entry points for data exchange.
• Databases: Storage mechanisms and access strategies.
• Caching Layers: Improving response times.
• Load Balancers: Ensuring traffic distribution.

5. Explain Data Flow

You need to articulate how data moves through the system:

• Request Handling: How user requests are processed by various components.
• Data Retrieval: How data is fetched from the database and returned.
• Concurrency: How the system handles multiple simultaneous requests.

Why Isn’t Coding Required?

• Focus on Architecture Over Syntax:
  The interviewer wants to test your understanding of systems at a high level—choosing the right tools, managing scale, and ensuring reliability. Code syntax or language specifics aren’t the priority.

• Real-World Complexity:
  Real systems rely on a combination of technologies rather than a single code snippet. Demonstrating how you choose and connect these technologies is more valuable than showing how you’d implement a small piece of logic.

When Minimal Coding Might Be Involved

In rare cases, you may be asked to write pseudo-code or logic snippets to:

• Illustrate how a specific algorithm works (e.g., URL shortening or consistent hashing).
• Explain component interactions or workflows in more detail.

This is typically about showcasing logic and understanding, not writing production-ready code.