What happens when we click on any website ,for instance amazon.com

Dec 12, 2024

User Input: You type amazon.com in your browser and hit enter.
URL Parsing: The browser parses the URL to extract components like protocol (http:// or https://), domain name (amazon.com), and path (e.g., /home).

The browser needs to convert the domain name (amazon.com) into an IP address.

Browser Cache: The browser checks its cache for a cached IP address of amazon.com.
Operating System Cache: If not in the browser cache, the OS cache is checked.
Local DNS Resolver: If not found, the query goes to the local DNS resolver (usually provided by your ISP).
Recursive DNS Lookup:
- The resolver queries root DNS servers to find the top-level domain (TLD) server (e.g., .com).
- The TLD server directs it to the authoritative DNS server for amazon.com.
- The authoritative server provides the IP address.

Once the IP address is obtained:

TCP Handshake: The browser establishes a TCP connection with the web server at the resolved IP using the three-way handshake:
- SYN: The client sends a synchronize packet.
- SYN-ACK: The server acknowledges.
- ACK: The client acknowledges, establishing the connection.
TLS Handshake (if HTTPS): For secure connections, the browser performs a TLS handshake to establish an encrypted connection.

The browser sends an HTTP or HTTPS request to the server for the desired resource:
- Method: GET (to fetch the webpage).
- Headers: Includes details like the browser type, cookies, etc.
The request may pass through intermediate entities like:
- Load Balancers: Distribute traffic among multiple servers.
- CDNs (Content Delivery Networks): Serve static resources (like images, JavaScript, and CSS) from geographically closer servers.

On the server side:

Routing:
- The load balancer routes the request to the appropriate web server.
- The web server (e.g., Nginx, Apache) routes it to the backend application.
Application Logic:
- The backend application processes the request.
- Queries are sent to databases for dynamic content.
- Business logic is applied to construct the response.
Microservices:
- For complex systems like Amazon, the request might invoke multiple microservices (e.g., product catalog, pricing, recommendations).

Cache Layer:
- Before querying the database, the server checks cache systems like Redis or Memcached for frequently requested data.
Database Query:
- If the cache doesn't have the data, a query is made to databases (e.g., MySQL, PostgreSQL, or NoSQL databases like DynamoDB).
The results are aggregated and returned to the backend application.

The server constructs the HTTP response:
- Status Code: e.g., 200 OK, 404 Not Found.
- Headers: Metadata about the response.
- Body: The HTML, CSS, JavaScript, or JSON data for the webpage.

The browser receives the response and:

Parses HTML: Builds the DOM (Document Object Model).
Fetches Resources:
- Loads additional CSS, JavaScript, and images referenced in the HTML.
- These may result in additional HTTP requests.
Executes JavaScript: Dynamically updates the DOM or interacts with APIs.
Renders the Page: The final page is displayed to the user.

Any interaction with the webpage (e.g., clicking a product) triggers additional HTTP requests, repeating some or all of the above steps.

DNS Resolution: Converts amazon.com to an IP address.
TCP/TLS Handshake: Establishes a connection with the server.
HTTP Request: Sends the request to the server.
Backend Processing: Handles the request using business logic, databases, and caches.
HTTP Response: Sends the response back to the client.
Browser Rendering: Displays the webpage to the user.

This intricate chain of events ensures that clicking amazon.com provides a fast, seamless, and secure experience.

Same process happens for all the websites

Shashank’s Substack