Getting Started with System Design Interviews#

System design interviews are one of the most challenging parts of the software engineering interview process. Unlike coding interviews, there is no single correct answer — instead, interviewers evaluate your ability to think through trade-offs and design scalable systems.

The STAR Framework for System Design#

When approaching a system design problem, use this structured approach:

1. Scope — Clarify requirements and constraints
2. Think — Brainstorm components and their interactions
3. Architect — Draw the high-level design
4. Refine — Dive deep into bottlenecks and trade-offs

Key Concepts to Master#

CAP Theorem#

The CAP theorem states that a distributed system can only guarantee two of three properties: Consistency, Availability, and Partition Tolerance.

Horizontal vs. Vertical Scaling#

• Vertical scaling: Add more power to existing machines (CPU, RAM)
• Horizontal scaling: Add more machines to distribute the load

Caching Strategies#

• Cache-aside (lazy loading)
• Write-through
• Write-behind
• Refresh-ahead

Common System Design Interview Topics#

1. Design a URL shortener (like Bit.ly)
2. Design a social media feed
3. Design a distributed message queue
4. Design a rate limiter
5. Design a CDN

Tips for Success#

• Always start by clarifying requirements
• Make reasonable assumptions and state them explicitly
• Start with a simple design and iterate
• Discuss trade-offs for every major decision
• Think about failure scenarios and how to handle them