Web Essentials

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