If you’ve ever wondered how a website like Instagram, YouTube, or Amazon can serve millions of users at the same time, the answer lies in how web servers are designed to handle many requests at once, without freezing or crashing. And behind all this magic are also things like IP addresses and NAT, which help route requests from your device to the correct server across the internet.
Let’s break this down in simple terms.
What Happens When You Visit a Website?
When you type a URL into your browser or open an app, your device sends a request to a web server. But how does your request know where to go? This is where the IP address comes in.
An IP address is like a street address for computers on the internet. Your request is sent to the server’s IP address—basically telling the internet, “Send this request to Instagram’s house.” But there’s more. Your device also has an IP address—though it’s usually a private one (like 192.168.1.10) that your router assigns.
So how does your private IP get on the public internet? That’s where NAT (Network Address Translation) comes in. Your home router uses NAT to take your private IP request, wrap it in a public IP address, and send it to the internet. When the web server replies, the router uses NAT again to forward the response back to the correct device in your house. This way, even though you and your sibling are on the same Wi-Fi network, websites can tell your requests apart.
The Restaurant Analogy
Now that the request has reached the server, think of the web server like a restaurant kitchen. Each user is a customer sending in an order (a request), and the kitchen (server) prepares the right dish (a response). A good kitchen doesn’t handle one order at a time—it handles many at once using a system to track what came in, who ordered it, and where it’s going.
The web server behaves the same way. It can respond to many requests at the same time, thanks to how it’s built.
Concurrency: Responding to Multiple Requests at Once
Servers use a concept called concurrency, which means handling multiple things at the same time. For example, a Node.js server uses an event loop, which allows it to respond to many users without pausing or getting stuck. It might start serving User A’s login, but while waiting for the database to respond, it begins working on User B’s photo feed—never sitting idle.
Other back-end systems, like those built in Python, Java, or Go, also use multi-threading or asynchronous models to keep up with the traffic.
Multiple Servers and Load Balancers
Big websites don’t rely on just one server. They use many servers around the world. When your request reaches Instagram’s system, a load balancer decides which server should handle it. Think of it like a restaurant host directing customers to different tables so no one waiter gets overloaded.
This keeps everything smooth, even when millions of users are active at the same time.
Databases Keep Up Too
The same goes for databases. When thousands of people like a post at once, the server sends that info to a powerful database system. These are designed to handle thousands of operations at once, without mixing anything up or slowing down.
In Summary
When you visit a website, your device sends a request using your private IP, which your router translates using NAT into a public request to the server’s IP address. Once the request reaches the server, it uses smart systems like concurrency, multi-threading, and load balancing to handle many users at once. It’s a mix of network routing and server-side logic that lets you and millions of others scroll, post, and message in real time—without even thinking about what’s happening behind the scenes.