System Design Framework

A structured approach to designing large-scale distributed systems. Apply these principles when architecting new services, reviewing designs, estimating capacity, or preparing for system design discussions.

Core Principle

Start with requirements, not solutions. Jumping to architecture before understanding constraints produces over- or under-engineered systems. Scalable systems are assembled from well-understood building blocks (load balancers, caches, queues, databases, CDNs) — the skill lies in choosing the right blocks, sizing them with estimates, and owning the tradeoffs each choice introduces.

Scoring

Goal: 10/10. Rate any system design 0-10: a 10/10 states requirements explicitly, includes back-of-the-envelope estimates, uses appropriate building blocks, addresses scaling and reliability, and acknowledges tradeoffs. Always state the current score and the specific improvements needed to reach 10/10.

The System Design Framework

Six areas for building reliable, scalable distributed systems:

1. The Four-Step Process

Core concept: Every design follows four stages: (1) understand the problem and establish scope, (2) propose a high-level design and get buy-in, (3) dive deep into critical components, (4) wrap up with tradeoffs and future improvements.