System Design Framework

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

Core Principle

Start with requirements, not solutions. Every system design begins by clarifying what you are building, for whom, and at what scale. Jumping to architecture before understanding constraints produces over-engineered or under-engineered systems.

The foundation: Scalable systems are not invented from scratch -- they are assembled from well-understood building blocks (load balancers, caches, queues, databases, CDNs) connected by clear data flows. The skill lies in choosing the right blocks, sizing them correctly, and understanding the tradeoffs each choice introduces. A four-step process -- scope, high-level design, deep dive, wrap-up -- keeps the design focused and communicable.

Scoring

Goal: 10/10. When reviewing or creating system designs, rate them 0-10 based on adherence to the principles below. A 10/10 means the design clearly states requirements, includes back-of-the-envelope estimates, uses appropriate building blocks, addresses scaling and reliability, and acknowledges tradeoffs. Lower scores indicate gaps to address. Always provide the current score and specific improvements needed to reach 10/10.

The System Design Framework

Six areas for building reliable, scalable distributed systems:

1. The Four-Step Process