How Clients and Servers Communicate

What You Will Learn

Understand the basic request-response model and the role of HTTP.

Core Idea

Most web applications use a client-server model.

The client could be a browser or mobile application. The server receives requests, performs business logic, communicates with other systems, and returns a response.

Client -> HTTP Request -> Server
Client <- HTTP Response <- Server

This simple model is the foundation for many larger systems.

A Simple Mental Model

Client
  |
  v
Application
  |
  +--> Database
  |
  +--> Cache
  |
  +--> Background Worker

Do not worry about building every component at once. System design is mainly about understanding why a component exists, what problem it solves, and how components communicate.

Practical Example

A login request might look like:

POST /api/login
Content-Type: application/json

{"email":"user@example.com","password":"secret"}

The server validates the credentials and returns a response such as:

{"token":"..."}

The system can later become distributed, but the basic request-response idea remains.

Key Points

['HTTP is a communication protocol used by many web systems.', 'Clients send requests.', 'Servers process requests and return responses.', 'APIs define how clients interact with services.']

Common Beginner Mistakes

Adding technologies before understanding the problem.
Designing for millions of users when the requirements do not justify it.
Ignoring failure cases.
Treating every system as if it needs the same architecture.
Focusing on diagrams instead of explaining the decisions behind them.

Quick Summary

The goal of this lesson is to build a simple mental model that you can reuse in future designs.

Next, you will learn how to design simple APIs that are predictable and easy to evolve.