The document discusses web servers and how they work. A web server is a program that satisfies client requests for web resources by hosting web pages. When a client makes a request, the web server parses it, checks authorization, associates the URL with a file, constructs a response, and transmits it back. Common Gateway Interface allows web servers to execute programs dynamically. Web servers also implement access control through authentication and authorization. Responses can be dynamically generated through server-side includes and scripts. Cookies are used to generate dynamic responses and maintain state across requests. Web servers can use different architectures like event-driven, process-driven, or hybrid.

1. WEB SERVER
DEBASISH DUARAH
Mtech-CSE
Pondicherry University

2. WEB SITE & WEB SERVER
• Web site : consist of a collection of web pages associated with a particular
hostname
• Web server : is a program to satisfy client request for web resources
• It used to host web pages but there exist different web servers for gaming, storage etc.

3. HOW IT HANDLES A CLIENT REQUEST ?
• Parsing the request message
• Checking that the URL is authorized
• Associating the URL in the request with a file
name
• Constructing the response message
• Transmitting the response message to the
requesting client

4. Common Gateway Interface offers a standard protocol for web servers to execute programs that execute
like console applications running on a server that generates web pages dynamically

5. ACCESS CONTROL
• Authentication
• Identifies the user who originated the request
• Name and password
• Authorization
• Determines which users have access to a particular resource
• Based on the information associated with the HTTP request(host name or ip address)

6. DYNAMICALLY GENERATED RESPONSES
• Server side include
• Instruct the web server to customize a static resources based on directives in an HTML-like file
• Server script
• Separate program that generates the request resource
• Program run as :
• Part of the server
• A separate process
• Role of web server:
• Associated with the URL with the appropriated script
• To pass the data to and from the script
• Role of script is
• Process the input from the server
• Generate the content to the client

7. CREATING AND USING COOKIES
• To generate dynamic responses cookies are used
• Browser asked to include a unique cookie in each HTTP request
• If the request doesn't include cookie, the script create a new cookie in the header
of the response message
• Set-cookie: customer:”user30”;version=“1”;path=“/book”
• Subsequent requests from the user would include the cookie
• Cookie: Customer=“user30”;version=“1”;path=“/book”
• Script can use COOKIE as user identifier in the interaction process

8. SHARING INFORMATION ACROSS REQUEST
• Server retain some information to reduce the overhead of handling future
request:
• Sharing HTTP responses across request
• Cache result is consistent with the primary copy of the information
• Sharing metadata across request
• Translation of url file
• Control information
• http response headers
• Server could also cache
• Current name
• Current date and time

9. SERVER ARCHITECTURE
• Event driven server architecture
• Process driven server architecture
• Hybrid server architecture

10. EVENT DRIVEN SERVER ARCHITECTURE
• Has a single process that alternates between servicing
different request
• Allows the server to serialize operation that modify the
same data
• Performs nonblocking systems calls
• Not used in most high end web servers

12. PROCESS DRIVEN SERVER ARCHITECTURE
• Allocates each request to a separate process
• One master process listens for new connection
• The master process creates or forks a separate process for new
connection.
• Terminate the process after parsing the client request and
transmitting the responses
• To prevent memory leak
• Introduces overhead for switching from one process to another

13. HYBRID SERVER ARCHITECTURE
• Strengths of the event driven and process driven models
are combined
• Each process would become an event driven server that
alternates between a small collection of request
• A single process has multiple independent threads.
• Main process instructs a separate helper process to
perform time consuming operations