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

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

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

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

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

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

System Architecture

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

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

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

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

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)

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

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’)

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)

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

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

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

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

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

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

Personal Web Server Personal Web Manager dialog.

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

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