How to Approach a System Design Interview

Learn the 4-step process to tackle system design interview questions effectively

The system design interview is an open-ended conversation. You are expected to lead it.

You can use the following steps to guide the discussion. To help solidify this process, work through common system design interview questions using the following framework.

1. Outline use cases, constraints, and assumptions

   Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

   Key questions to ask:

   • Who is going to use it?
   • How are they going to use it?
   • How many users are there?
   • What does the system do?
   • What are the inputs and outputs of the system?
   • How much data do we expect to handle?
   • How many requests per second do we expect?
   • What is the expected read to write ratio?

   Start by clearly defining the problem scope. This prevents you from solving the wrong problem and demonstrates your ability to gather requirements.

2. Create a high level design

   Outline a high level design with all important components.

   What to include:

   • Sketch the main components and connections
   • Justify your ideas

   Focus on the big picture first. You’ll dive into details in the next step. Use simple boxes and arrows to show how components interact.

3. Design core components

   Dive into details for each core component. For example, if you were asked to design a URL shortening service, discuss:

   Example considerations:

   • Generating and storing a hash of the full URL
     • MD5 and Base62 encoding
     • Hash collisions
     • SQL or NoSQL
     • Database schema
   • Translating a hashed URL to the full URL
     • Database lookup
   • API and object-oriented design

   This is where you demonstrate deep technical knowledge. Be prepared to discuss trade-offs between different approaches.

4. Scale the design

   Identify and address bottlenecks, given the constraints. For example, do you need the following to address scalability issues?

   Common scaling solutions:

   • Load balancer
   • Horizontal scaling
   • Caching
   • Database sharding

   Discuss potential solutions and trade-offs. Everything is a trade-off. Address bottlenecks using principles of scalable system design.

   Don’t just add components - explain why each scaling solution is necessary and what problems it solves. Discuss the trade-offs of each approach.

Additional Resources

Check out the following links to get a better idea of what to expect:

• How to ace a systems design interview
• The system design interview
• Intro to Architecture and Systems Design Interviews
• System design template