What to ask in a system design interview?

Asking the right questions in a system design interview is crucial. It not only helps you clarify the problem and align your understanding with the interviewer's expectations but also demonstrates your critical thinking and attention to detail. Here's a guide on what to ask in a system design interview:

1. Clarify the Requirements

What are the core functionalities of the system?
- Example: "What are the primary features that this system needs to support?"
What are the non-functional requirements (NFRs)?
- Example: "Are there any specific performance, scalability, or security requirements?"
What is the scale of the system?
- Example: "How many users or requests per second should the system be able to handle?"
Are there any specific constraints?
- Example: "Are there any limitations or constraints I should be aware of, such as budget, time, or technology stack?"

2. Understand the Users

Who are the users of the system?
- Example: "Who will be using this system, and what are their key needs?"
How will users interact with the system?
- Example: "Will the users interact with this system via a web interface, mobile app, or APIs?"

3. Define the Data

What type of data will the system handle?
- Example: "Can you describe the types of data that the system needs to store and manage?"
What are the data storage requirements?
- Example: "How much data do we expect to store, and how long should it be retained?"
Is the data structured, semi-structured, or unstructured?
- Example: "What is the nature of the data? Is it structured (e.g., SQL databases) or unstructured (e.g., logs, media files)?"

4. Explore the Workflow

What is the expected user flow?
- Example: "Can you walk me through a typical user journey or workflow in this system?"
Are there any critical paths or processes?
- Example: "Are there any specific processes or flows that are particularly important to the system's success?"

5. Understand the Scale and Load

What is the expected traffic or load?
- Example: "What is the anticipated traffic in terms of requests per second or users per day?"
Are there peak usage times?
- Example: "Does the system need to handle spikes in traffic, such as during a sale or event?"

6. Consider Security and Compliance

What are the security requirements?
- Example: "Are there specific security concerns, such as user authentication, data encryption, or access control?"
Are there compliance or regulatory requirements?
- Example: "Does the system need to comply with regulations such as GDPR or HIPAA?"

7. Ask About Integration and Dependencies

Does the system need to integrate with other services?
- Example: "Does the system need to interact with any external services, APIs, or databases?"
What dependencies does the system have?
- Example: "Are there any existing systems or services that this system will depend on?"

8. Clarify Performance Expectations

What are the performance expectations?
- Example: "What are the response time and latency requirements for key operations?"
Are there specific performance metrics to meet?
- Example: "Are there any specific performance metrics or SLAs (Service Level Agreements) that the system needs to meet?"

9. Discuss Future Scalability and Extensibility

How do you foresee the system evolving?
- Example: "Are there any planned future features or expansions that the design should accommodate?"
What are the growth expectations?
- Example: "How much growth in terms of users or data do you anticipate in the next few years?"

10. Inquire About Failure Handling and Recovery

How should the system handle failures?
- Example: "What are the expectations around fault tolerance and handling failures?"
What is the disaster recovery plan?
- Example: "What is the plan for disaster recovery, and how quickly does the system need to recover?"

11. Ask About Monitoring and Maintenance

How will the system be monitored?
- Example: "What monitoring and logging solutions should be in place to track system health and performance?"
What are the maintenance expectations?
- Example: "Are there any specific maintenance requirements or considerations for the system?"

12. Understand Priorities and Trade-offs

What are the most important aspects of the system?
- Example: "Among performance, reliability, security, and cost, which is the highest priority?"
Are there any trade-offs to consider?
- Example: "Are there any trade-offs that you are particularly concerned about, such as sacrificing performance for lower cost?"

13. Ask About the Technology Stack

Is there a preferred technology stack?
- Example: "Is there a preferred technology stack, or do I have the flexibility to choose?"
Are there any existing tools or platforms?
- Example: "Are there any existing tools, platforms, or frameworks that we should leverage in the design?"

14. Determine the Development and Deployment Strategy

What is the development timeline?
- Example: "What is the expected timeline for developing and deploying the system?"
What is the deployment environment?
- Example: "Will this system be deployed on-premises, in the cloud, or in a hybrid environment?"

15. Wrap Up with Open-Ended Questions

Is there anything else I should consider?
- Example: "Is there anything else that we haven't discussed that is important for the system's design?"
Are there any specific challenges you anticipate?
- Example: "Are there any specific challenges or risks that I should be aware of when designing this system?"

Conclusion

Asking these questions not only helps you gather the necessary information to design a robust system but also shows the interviewer that you are thorough, thoughtful, and capable of considering all aspects of system design. It’s important to approach the interview as a collaborative discussion, demonstrating your ability to ask the right questions and think critically about the problem.