System Design Interview Framework

Importance of a Framework

• Stressful Environment: Interviews are high-pressure with limited time to showcase abilities.
• Need for Structure: Prevents time waste and makes it easier for the interviewer to follow.
• Benefits: A structured approach ensures asking the right questions and focusing on what's essential.

4-Step Framework

1. Understand the Problem & Establish Design Scope
2. Propose High-Level Design & Get Buy-In
3. Design Deep Dive
4. Wrap-Up

Typical Interview Timing

• Introduction: 5 minutes
• Q&A: 5 minutes
• Main Content: 35-45 minutes
• Suggested Time Allocation: Step 1: 5 mins, Step 2: 20 mins, Step 3: 15 mins, Step 4: 5 mins
• Consider this a rough guide; adjust as necessary.

Step 1: Understand the Problem & Establish Design Scope

• Nature of Questions: Typically open-ended and sometimes vague.
• Objective: Organize thoughts and pinpoint essential aspects.
• Avoid Premature Solutions: Ask questions to fully understand the problem first.
• Key Questions to Ask:
  • Why are we building this system?
  • Who are the users?
  • What features are needed?
• Feature Prioritization: Agree on top features with the interviewer.
• Non-Functional Requirements: Focus on scale and performance.
• Scale Estimation:
  • Perform back-of-the-envelope calculations.
  • Get a general sense of the system’s scale and order of magnitude.

Step 2: Propose High-Level Design & Get Buy-In

• Approach: Top-down, starting with APIs.
• API Design:
  • Follow RESTful conventions unless specified otherwise.
  • Define input parameters and output responses.
  • Ensure APIs meet functional requirements.
  • Avoid unnecessary APIs.
• Two-Way Communication: Use WebSocket for client-server communication if needed; be mindful of its stateful nature.
• High-Level Design Diagram:
  • Starts with load balancers or API gateways.
  • Services that meet feature requirements.
  • Data storage layer (do not specify technology yet).
• Data Model & Schema:
  • Assess data access patterns and read/write ratio.
  • Impact of data modeling on performance.
  • Consider the indexing options.
  • Referral to the deep dive section if data modeling is critical.
• Review: Make sure all features are covered end-to-end.

Step 3: Design Deep Dive

• Objective: Identify and address potential problems and trade-offs.
• Interview Collaboration: Decide what areas to dive deeper into.
• Importance of Non-Functional Requirements: Critical for higher-level roles.
• Approach:
  • Read the Room: Pay attention to interviewer’s feedback.
  • Problem Articulation: Clearly state the issue (e.g., high write QPS).
  • Multiple Solutions: Propose at least two solutions and discuss trade-offs.
  • Supported by Data: Use numbers to back up decisions.
• Typical Coverage: Usually dive into top 2 or 3 issues.

Step 4: Wrap-Up

• Summary: Highlight unique aspects of the design.
• Q&A: Leave time to ask the interviewer about the company.

Additional Resources

• Newsletter: Newsletter offers insights on large-scale system designs. Subscribe at blog.bytebytego.com