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Web Servers

Presented byMohamed Zeinelabdeen Abdelgader

Sudan University for Science and Technology

College of graduate studiesMsc in Computer Science

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Presentation Outline

An Over View Web Clients and Web Servers Dynamic & Static Content System Architecture Request methods. Accessing web servers Request Handling Phases Most Famous Web Servers Selecting a web server

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Various Meanings of “Server” Server

Computer used to provide files or make programs available to other computers

Server software Used by a server computer to make files and programs available

to other computers Many types of server

FTP server : remote file space, often read-only Mail server : email system News server : newsgroups messages

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Web Clients and Web Servers Client/server architectures

Client computers typically request services

Server processes clients’ requests.

Web server

a computer program that delivers (serves) content, such as web pages, using the Hypertext Transfer Protocol (HTTP), over the World Wide Web.

The term web server can also refer to the computer or virtual machine running the program.

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Platform Neutrality of the WebLets different types of computers, running different operating systems,

communicate

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Static & Dynamic Content

Static page

Unchanging page retrieved from server

Dynamic page

Web page whose content is shaped by a program in response to user requests

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Dynamic Content (cont)

Server-side scripting Programs running on a Web server to create Web pages

before sending them back to the requesting Web clients

Dynamic page-generation technologies Active Server Pages (ASP)

JavaServer Pages (JSP)

Hypertext Preprocessor (PHP)

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Two-Tier Client/Server Architecture Request message

Message that a Web client sends to request a file or files from a Web server

Typical request message Request line

Optional request headers

Optional entity body

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Message Flows in a Two-Tier Client/Server

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Two-Tier Client/Server Architecture (cont)

Request line Contains a command, the name of the target resource, and

the protocol name and version number

Request headers Can contain information about types of files that the client

will accept in response to a request

Entity body Used to pass bulk information to the server

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Three-Tier or N-Tier Client/Server Architectures

Three-tier architecture

Extends two-tier architecture to allow additional processing

Third tier includes software applications that supply information to the Web server

Sometimes know as N-tier or multi-tier architectures

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Message Flows in a Three-Tier Client/Server

Client tier Middle tier

Information tier

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Request methods (GET)

The get request sends form content as part of the URL .

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Request methods (POST)

The data sent in a post request are not part of the URL and cannot be seen by the user.

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Accessing web servers

Must know host name on which web server resides

Remote web servers accessed using

• URL: http://www.dtl.com/default.asp

• OR IP address http://207.60.134.230

Local web servers (on same machine) accessed using machine name or localhost

Protocol Domain name

Page name

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Request Handling Phases

URI to filename translation; Check access based on host address, and other

available information; Get an user id from the HTTP request and validate it; Authorize the user; Determine the Multipurpose Internet Mail Extensions

(MIME) type of the requested object (the content type, the encoding and the language);

Fix-ups (for example replace aliases by the actual path); Send the actual data back to the client; Log the request;

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Most Famous Web Servers

Apache HTTP Server from Apache Software Foundation Internet Information Services (IIS) from Microsoft Sun Java Web Server from Sun Microsystems

Formerly Sun ONE Web Server, iPlanet Web Server, and Netscape Enterprise Server

Zeus Web Server from Zeus Technology

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Apache HTTP Server

Ongoing group software development effort

Dominated the Web since 1996 because it is free and performs efficiently

Apache

Developed by Rob McCool at the University of Illinois in1994 at the National Center for Supercomputing Applications (NCSA)

Currently available on the Web at no cost as open-source software

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Microsoft Internet Information Server

Comes bundled with current versions of Microsoft Windows Server operating systems

Used on many corporate intranets

Supports the use of

ASP

ActiveX Data Objects

SQL database queries

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Sun Java System Web Server (Sun ONE, iPlanet, Netscape) Descendant of the original NCSA Web server program Formerly sold under the names

Sun ONE Netscape Enterprise Server iPlanet Enterprise Server

Charges between $1400 and $5000 for the licensing fee

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Selecting a web serverVarious criteria

Performance e.g. how many client

requests per second can be processed? Load balancing?

Ease of Use

How easy to set up , administer, learn?

Support

What support is provided by the

vendor?

Reliability

How robust is the web server? How liable to crash? How easily recovered?

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Selecting a web server (cont.)

Functionality•server side techologies supported?

e.g. ASP? JSP? etc

Price

How must does it cost to

buy and maintain?

Operating system

What operating system(s) does the web server support?

Security

What security functionality

is offered? e.g. Secure Sockets Layer SSL?

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Conclusion

Web servers respond to client requests by providing resources.

A Web server is part of a multi-tier application. A multi-tier application divides functionality into separate tiers. The three-tier application contains an information tier, a middle tier and a client tier.

The most common HTTP request types are get and post. Selecting a web server depended on (Performance,

Reliability, Support, Functionality, Ease of Use, Price, Security, Operating system).

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References

Internet & World Wide Web How to Program (4nd Edition)

http://www.serverwatch.com/tutorials/article.php/1363221

http://www.macronimous.com/resources/web_servers_demystifyed.asp

http://www.w3.org/Servers.html http://en.wikipedia.org/wiki/Web_server

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