System Design From Scratch: The Components That Actually Run Production Systems

DNS comes first and returns the IP for a domain name.

In the example, amazon.com resolves to 10.5.8.2.

A request may then pass through a CDN edge, rate limiter, load balancer, API gateway, microservice, and Redis cache.

A client sends the request; it can be a phone, laptop, or smart fridge.

Vertical scaling upgrades one machine, while horizontal scaling adds identical servers that can keep serving if one goes down.