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Introduction to System Design
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Pretend you know nothing about tech. You still use systems every day.
Imagine your friend is cooking a meal for 5 people. Easy — one pan, one stove, done. Now imagine cooking for 5,000 people at a wedding. You need multiple chefs, multiple stations, a way to coordinate orders, storage for ingredients, and a plan for when one chef calls in sick. That coordination problem is exactly what system design solves — but for software.
Every app you use — WhatsApp, Zomato, Instagram, Paytm — is just a lot of computers talking to each other in a very organised way. System design is the blueprint for how they talk, who does what, and what happens when something breaks.
Your phone is the Customer
When you tap Send on WhatsApp, your phone is asking a question: "Please deliver this message." That question travels over the internet to WhatsApp's computers.
A Traffic Manager picks the right worker
WhatsApp has thousands of computers. A Load Balancer acts like a traffic manager at a toll booth — it picks the least-busy computer to handle your request so nobody gets overloaded.
A Worker saves the message and notifies the recipient
The chosen computer (API Server) does two things: saves your message to a storage system (Database) so it is never lost, and sends a knock (notification) to your friend's phone via a delivery queue.
Nearby server delivers photos and videos
Pictures and videos are heavy. Instead of sending them from one far-away computer, a CDN stores copies near both of you — like a local courier warehouse instead of shipping from another city.
System design is just answering: who are the workers, how do they communicate, what happens when one is absent, and how do we serve a billion customers without anyone waiting too long?