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How does a web page renders

May 16, 2011

A Website is a collection of Web page, where a web page is a document that is suitable for the World Wide Web and can be accessed through a web browser which is displayed on a monitor or mobile device. The information is usually in HTML or XHTML formats and may provides navigation to other web pages through hyperlinks. Generally, you enter a web address in a browser, the browser loads for a period of time, then it displays a web page. Have you ever thought, what actually happens at the backend? How the web page is displayed? The process is not as simple as you think.

  • You type a web address in the browser, for e.g. http://www.somedomain.com
  • The browser parses the URL to find its protocol (HTTP or HTTPS), host (www.somedomain.com) and path (/goto/aboutme.php)
  • To reach the host, it first needs to translate the human readable host into an IP address. This process is done by DNS (Domain Name System), it translates domain names to numerical identifier.
  • A HTTP request is created.

    TCP/IP Protocol

    • Transmission Control Protocol, Internet Protocol (TCP/IP) is a communication protocol used to connect a computer system in a network.
    • Hyper Text Transfer Protocol (HTTP) is a member of TCP/IP family.
    • It is the communication for the World Wide Web.
    • HTTP functions as a request-response protocol. The browser submits the HTTP request to the server and the server response back.
    • The HTTP contains informations like source and destination address, contents and the port number.
  • The request passes the Web Application Firewall, analyses the OSI layers-7 messages for violation in the programmed security policy. It is a security device protecting the web server from the attack. They look at every request and response within the HTTP/HTTPS/SOAP/Web Services layers. Firewalls can be software or hardware appliances based and are installed in front of a web server in an effort to shield it from the incoming attacks.
  • The host forwards the request to the web server, configured to listen on the specified port.
  • The server checks the request and launches the server plug-in needed to handle the request (corresponding the server language like PHP, JAVA, PERL, Python).
  • The plug-in gets full access to the HTTP request and starts to prepare the HTTP response (parses CSS, Javascript etc).
  • If the request has some database connection, the connection is created and the query is executed.
  • Data from the database, together with other information is combined into long string of text (probably a HTML)
  • The browser receives the response and converts to HTML.
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From → World Wide Web

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