The System Design Metro — An Interactive Playbook

The problem it solves: humans and apps refer to servers by name (api.example.com), but the network only understands numeric IP addresses.
The trick beginners miss: DNS isn't just a static lookup table. With geo-DNS or anycast , the same name can resolve to a different, nearer IP address depending on where the request comes from — this is the very first load-balancing decision, made before a single packet reaches your infrastructure.
Why it matters at scale: DNS records are cached (with a Time-To-Live) by browsers, OSes, and ISPs — cheap and fast, but it means changes to where traffic points can take time to fully propagate.

System Design Metro

an interactive playbook · 20 stations

Overview & Metro Map

The Universal Blueprint

Product Archetypes

Case studies — 20 stations

System Design Metro / Overview

beginner-friendly · 20 case studies

Built as a teaching tool. Every architecture shown is a simplified, directionally-accurate model of publicly discussed patterns — real systems have more nuance, more failure modes, and more history behind every decision.