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 Middle 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 Local Web server
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 http://www.microsoft.com
Apache and Tomcat documentation
Apache and Tomcat are free to download and install
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