How to approach a system design interview question

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

Step 1: Outline use cases, constraints, and assumptions.

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

Question examples:

• 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 and write ratio?

Step 2: Create a high level design

Outline a high level design with all important components.

• Sketch the main components and connections
• Justify your ideas

Step 3: Design core components

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

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

Step 4: Scale the Design

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

• Load balancer
• Horizontal scaling
• Caching
• Database sharding