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

You open amazon.com. A product page loads in under a second. Behind that single page load, your request hit a DNS server, bounced through a CDN edge node, passed a rate limiter, got distributed by a load balancer, routed by an API gateway, processed by a microservice, checked a Redis cache, and maybe — maybe — touched an actual database. That's system design. Not theory. Not whiteboard boxes. The actual machinery that keeps websites alive when millions of people use them at the same time. Here's how each piece works, why it exists, and when you need it. The Client-Server Relationship and DNS Everything starts with two things: a client and a server. The client is whatever device makes the request — your phone, laptop, a smart fridge, doesn't matter. The server is a machine that runs 24/7 with a public IP address, sitting in a data center somewhere, waiting for requests. The problem is that IP addresses look like 10.5.8.2 . Nobody remembers that. So we have DNS — the Domain Name System —