How Browser Requests Reach Web Servers? Step-by-Step Details

Each time a user enters a website address, clicks a bookmark, or fills out an online form, a highly complex digital interaction takes place within seconds. 

Every successful load of a web page involves a certain pattern of communication between client-side software and distant hardware systems. Exploring how a web page request works reveals the basics of how the internet works today.

Step 1: Resolution of the Domain Name through DNS

The Internet Protocol (IP) addresses, rather than human-readable website addresses such as example.com, are used by computers for routing information over physical networks.

When a user enters an address, the browser first tries to look up the address in its cache to see if there is an IP address for it. 

However, if not, then the browser makes a request to the Domain Name System (DNS), which acts as the internet’s digital telephone directory and locates the relevant IP address of the website server.

Step 2: Creating a Secure Connection

Once the IP address of the server is known by the browser, there must be a connection made before data is transferred.

• TCP Handshake: The browser creates a TCP three-way handshake message (SYN, SYN-ACK, ACK) to the web server. It simply means that both the client and server are prepared for packet transmission.
• TLS/SSL Encryption: In a secure HTTPS website, the devices perform a TLS handshake process, which includes the server providing a digital certificate to the browser and agreeing on encryption keys.

Step 3: Transferring the HTTP Request

Once the TCP/TLS connection has been made, the browser will formulate the Hypertext Transfer Protocol (HTTP or HTTPS) request to be sent to the server. There are a number of essential components to an HTTP request:

• HTTP Method: Specifies the type of action that the client wishes to make, e.g., GET (to retrieve a page) or POST (to send data).
• HTTP Header: Contains a number of pieces of information, such as which browser was used (User-Agent) and the language and session cookies.
• HTTP Path and Body: The actual file or resource needed (e.g., /index.html) and any user input.

Step 4: Web Server Processes Request and HTTP Response

After the request is processed by the web server, it sends the message internally to the appropriate procedure. In case of a static request, the file gets accessed on the disk. 

However, when there is a dynamic request, the application server processes back-end code written in programming languages such as Python, Node.js, and PHP. 

Moreover, the database is accessed in order to generate customized content for each client. The above result is then packaged in an HTTP response including:

• Status Code: Status of the request processed, i.e., 200 OK for a successfully processed request and 404 Not Found for an unsuccessful request.
• Header: Additional information such as type of content, caching and security policies.
• Body: Raw content such as HTML, CSS, JavaScript, or JSON.

Step 5: Rendering the Webpage in the Browser

It is not the end of the browser request process once it receives an initial HTTP response. After getting the plain HTML code, the browser starts rendering the page using its rendering engine:

• HTML & CSS PARSING: The browser parses the HTML code to create a DOM tree and then merges it with the CSS parsing, creating the render tree.
• Loading Dependencies: When the browser loads the HTML code, it discovers that there are dependencies in the form of fonts, scripts, and images that make the browser issue new HTTP requests for each.
• Layout & Painting: The browser computes exact screen locations for all elements and draws them visually on the screen, making the webpage interactive.

Conclusion

Coordination is required to deliver data across the web in an orchestrated manner by clients, network protocols, and remote hosts. This process of browser requests, from initial DNS lookups and TCP handshakes through HTTP response cycles and rendering the page, provides a rich interactive experience in a fraction of a second.

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