# Web Development Essentials

## Client-Server Architecture

**Basic Communication Flow:**

* **Client** (Browser) sends a **REQUEST (REQ)** to the server
* **Server** (Instagram, in the example) processes and sends back a **RESPONSE (RES)**
* This is the foundation of how web applications work

**HTTP Status Codes:**

* **2xx** → Success (200 = OK)
* **3xx** → Redirection
* **4xx** → Client Error (404 = Not Found)
* **5xx** → Server Error (500 = Internal Server Error)

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## HTML (Hyper Text Markup Language)

**Purpose:**

* Defines the structure of webpages
* The skeleton/framework of web content

**Web Terminology:**

* **Webpage** = Single HTML document
* **Website** = Collection of multiple webpages
* **WebApp** = Dynamic, interactive application

**Site Types:**

* **Static Sites** → Content doesn't change without manual updates
* **Dynamic Sites** → Content changes based on user interaction or data

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## Domain Name System (DNS)

**What it does:**

* Translates human-readable domain names into IP addresses
* Acts like a phonebook for the internet

**How it works:**

1. User types `google.com` in browser
2. Request goes to DNS server
3. DNS looks up the IP address (e.g., `45.52.89.12`)
4. Browser connects to that IP address to reach the server

**IP Address Format:**

* Example: `192.168.1.5`
* Range: `0-255` for each segment
* Four segments separated by dots

**Key Concept:**

* Domain names are easier to remember than IP addresses
* DNS maintains a mapping table of Domain Names → IP Addresses
* Servers are identified by IP addresses on the network