Client-Server-API model

Back Client-Server-API model 08 Oct, 2025

ABHISHEK AGNIHOTRI

🧩 The Big Picture

When you open a website, use a mobile app, or even talk to Alexa — a “client” (you or your device) is asking for something, and a “server” is the one giving it back.

This entire back-and-forth conversation is made possible using APIs (Application Programming Interfaces) — like waiters passing your order between you and the kitchen.

🍽️ Real-Life Example: Restaurant Analogy

Term	Real-Life Example	Tech Equivalent
🧑‍💼 Client	You sitting at the restaurant table	Your browser, phone app, or computer
🧾 API	The waiter who takes your order to the kitchen	The middleman that carries your request to the server
👨‍🍳 Server	The kitchen that prepares your food	The computer that processes your request and gives a response
🍲 Response	The food delivered back to your table	The data returned (like a webpage, image, or JSON data)

💡 What Actually Happens (Step-by-Step)

1️⃣ Client makes a Request

You (the client) want something — like opening www.notechit.com.

Your browser sends a request to that website’s server asking:

“Hey, please give me the homepage of Notechit.”

This is like you telling the waiter:

“I want a pizza!”

2️⃣ The Server receives the Request

The server is a powerful computer (somewhere in the cloud) that receives your message.
It’s like the restaurant kitchen receiving your pizza order.

It checks:

What is the client asking for?
Do I have permission to give it?
How should I prepare the answer?

3️⃣ The Server Processes and Responds

The server does the work — maybe fetching data from a database, or performing logic.

Then it sends a Response back to the client.
For example:

{
  "message": "Welcome to Notechit!",
  "status": 200
}

That’s like the kitchen preparing your pizza 🍕 and the waiter bringing it to you.

4️⃣ The Client Displays the Result

Finally, your browser or app shows you what the server sent —
that could be:

A webpage
An image
A message
Some data

You just see the final “pizza,” not how it was made behind the scenes.

⚙️ API Requests and Their “Methods”

APIs use HTTP Methods — think of them as types of restaurant orders.
Each tells the server what kind of action you want to perform.

Method	Purpose	Analogy
GET	Fetch something	“Can I see the menu?”
POST	Add or send something	“I’d like to order a pizza.”
PUT	Update or replace something	“Change my pizza topping to mushrooms.”
PATCH	Partially update something	“Add olives only.”
DELETE	Remove something	“Cancel my pizza order.”

So when your app sends:

GET /users

It means — “Please get me all users.”

And if it sends:

POST /users

It means — “I want to create a new user.”

🧠 Behind the Scenes (Simplified)

Here’s what happens technically:

Client → sends HTTP request → https://api.notechit.com/getUser
Internet (Network) → delivers request → to the Server
Server → processes, gets data from Database
Server → sends HTTP response → back to Client
Client → interprets and displays data on screen

🌍 Example in Action (Simple FastAPI Example)

Let’s see how it works in Python using FastAPI:

from fastapi import FastAPI

app = FastAPI()

@app.get("/welcome")
def greet_user():
    return {"message": "Hello Abhishek, welcome to Notechit!"}

👉 When you open http://127.0.0.1:8000/welcome

Client (browser) sends GET /welcome
Server (FastAPI app) receives it, runs greet_user()
Sends back JSON response: {"message": "Hello Abhishek, welcome to Notechit!"}

🧭 Summary (In Layman Terms)

Concept	Meaning	Analogy
Client	Who asks for something	You at a restaurant
Server	Who provides the answer	The kitchen
API	The messenger between both	The waiter
Request	The order	What you want
Response	The delivery	What you get
HTTP Methods	Type of action	Order type (get, post, update, cancel)

🧠 Quick Visual Flow

[ CLIENT ]  --->  [ API Request ]  --->  [ SERVER ]
     ↑                                   ↓
     <---  [ API Response ]  <------------