Web Servers

1. Web Servers • How do our requests for resources on the Internet get handled? • Can they be located anywhere? Global?

2. Web Servers • Looking at …. • Introduction to web servers • HTTP request types • 3-tier system architecture • Accessing a web server (local and remote) • Web server examples • Apache • Tomcat • IIS • PWS

3. What is a web server? • Web server • Specialized software that responds to client requests by providing resources (web pages, documents, etc..) • Based on the client/server model • When users enter URL into Web browsers, they request specific documents from Web server • Maps URL to file on server and returns requested document to client • Communicates with client using HTTP • Protocol for transferring requests and files over the Internet

4. HTTP Request Types • Also known as request methods • Most popular are get and post • Retrieve and send client form data to Web server • get request • Sends form content as part of URL • Retrieves appropriate resource from Web server • Limits query to 1024 characters • post request • Updates contents of Web server (posting new messages to forum) • Has no limit for length of query • Not part of URL and cannot be seen by user

5. HTTP Request Types • get and post requests are sent to a server-side form handler • Client browsers cache (save on disk) Web pages • Allows for quick reloading • Cache responses to get request • Do not cache responses to post request

6. System Architecture • A web server forms part of a multi-tier application • Divide functionality into separate tiers • Logical groupings of functionality • Can reside on same computer or on different computers • What does a 3-tier architecture look like? • let’s have a look

7. System Architecture

8. System Architecture • Client tier • Referred to as the top tier • Application’s user interface • Users interact with application through user interface • Interacts with middle tier to make requests and to retrieve data from information tier • Displays data to user

9. System Architecture • Information tier • Referred to as data tier or bottom tier • Maintains data for application • Stores data in relational database management system • Middle tier • Implements business logic and presentation logic • Controls interactions between application clients and application data • Acts as intermediary between data in information tier and application clients

10. System Architecture • Middle tier, cont. • Controller logic • Processes client requests from top tier • Retrieves data from database • Presentation logic • Processes data from information tier • Presents content to client • Business logic • Enforces business rules • Dictates how clients can access application data and how applications process data • Ensures data validity before updating database

11. Accessing Web Server • Requesting documents • Must know machine name on which Web server resides • Through local Web servers or remote Web servers • Through domain name or Internet Protocol (IP) address • Local Web server • Resides on users’ machines • Requests documents in two ways • Machine name • localhost • Host name that references local machine

12. Accessing Web Server • Remote Web server • Resides on different machines • Accessing resources on remote web server requires • Domain name • Represents group of hosts on Internet • Combines with how name (www) and top-level domain to from fully qualified host name • Fully qualified host name • Provides user friendly way to identify site on Internet • IP address • Unique address for locating computers on Internet • DNS (see notes)

13. Examples of Web Servers • Apache (Apache group) • Tomcat (Apache group) • IIS (Microsoft Internet Information Services) • PWS (Microsoft Personal Web Server)

14. Apache web server • Apache • Maintained by Apache Software Foundation • Currently most popular Web server • Stable • Efficient • Portable • (got it’s name from the original developers who called it ‘a patchy server’)

15. Apache web server • Open source • Freely distributed on the Internet • Huge amount of end-user support • Has earned the reputation of being one of the most reliable web server available • Uses server modules to add functionality to the core HTTP server • i.e. extra services that it can provide (e.g. security authentication)

16. Apache web server • To launch Apache, successively select • Start, Programs, Apache httpd Server, Control Apache Server and Start

17. Tomcat web server • Tomcat • Similar to Apache and also maintained by Apache Software Foundation • Fast becoming a popular Web server • Built in Servlet container (engine) • Requires no add-ons to support Servlets

18. Tomcat web server • To launch Tomcat, successively select • Start, Programs, Apache Tomcat 4.x and Start Tomcat

19. Internet Information Services (IIS) web server • Developed by Microsoft • IIS 5.0 • Enterprise-level Web server • Included with Windows 2000 • Allows computer to serve documents • Uses an Internet Services Manager to administrate • see diagram

20. Internet Information Services (IIS) web server Internet Services Manager dialog.

21. Personal Web Server (PWS) • PWS developed by Microsoft • PWS • Scaled-down version of IIS • Intended for personal computers (PC) • Ideal for educational institutions, small businesses and individuals • Does not require PC to be used exclusively as Web server • A Personal Web Manager is used to administrate it

22. Personal Web Server Personal Web Manager dialog.

23. References • Check out • http://www.apache.org • Apache and Tomcat documentation • Apache and Tomcat are free to download and install • http://www.microsoft.com • IIS and PWS documentation

24. Summary • We have looked at: • Introduction to web servers • HTTP request types • 3-tier system architecture • Accessing a web server (local and remote) • Web server examples