MODULE: 2 WEB SERVER HARDWARE AND SOFTWARE A server is a system (software and suitable computer hardware) that responds to requests across a computer network to provide, or help to provide, a network service. Servers can be run on a dedicated computer, which is also often referred to as 'the server', but many networked computers are capable of hosting servers. In many cases a computer can provide several services and have several servers running. A server is any computer used to provide (or “serve”) files or make programs available to other computers connected to it through a network (such as a LAN or a WAN). The software that the server computer uses to make these files and programs available to the other computers is sometimes called server software. Sometimes this server software is included as part of the operating system that is running on the server computer. Thus, some information systems professionals informally refer to the operating system software on a server computer as server software, a practice that adds considerable confusion to the use of the term “server.” In short, Server refers to a computer or device on a network that manages network resources. Types of servers In a general network environment the following types of servers may be found. Application server, a server dedicated to running certain software applications Catalog server, a central search point for information across a distributed network Communications server, carrier-grade computing platform for communications networks Compute server, a server intended for intensive (esp. scientific) computations Database server, provides database services to other computer programs or computers Fax server, provides fax services for clients File server, provides remote access to files Game server, a server that video game clients connect to in order to play online together Home server, a server for the home Print server, provides printer services Proxy server, acts as an intermediary for requests from clients seeking resources from other servers Sound server, provides multimedia broadcasting, streaming. Stand-alone server, a server on a Windows network that neither belongs to nor governs a Windows domain Web server, a server that HTTP clients connect to in order to send commands and receive responses along with data contents Web server can refer to either the hardware (the computer) or the software (the computer application) that helps to deliver web content that can be accessed through the Internet. The most common use of web servers is to host websites, but there are other uses such as gaming, data storage or running enterprise applications. The primary function of a web server is to deliver web pages on the request of clients using the Hypertext Transfer Protocol (HTTP). This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and scripts. Web servers are not always used for serving the World Wide Web. They can also be found embedded in devices such as printers, routers, webcams and serving only a local network. The web server may then be used as a part of a system for monitoring and/or administering the device in question. This usually means that no additional software has to be installed on the client computer; since only a web browser is required. BY: VIKRAM.G.B 1 Lecturer, P.G Dept of Commerce Vivekananda Degree College, Bangalore-55 Web servers are computers that deliver (serves up) Web pages. Every Web server has an IP address and possibly a domain name. For example, if you enter the URL http://www.pcwebopedia.com/index.html in your browser, this sends a request to the Web server whose domain name is pcwebopedia.com. The server then fetches the page named index.html and sends it to your browser. Any computer can be turned into a Web server by installing server software and connecting the machine to the Internet. There are many Web server software applications, including public domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape and others. Web Client/Server Communication: When a person uses a Web browser to visit a Web site, the Web browser (also known as a Web client) requests files from the Web server at the company or organization that operates the Web site. Using the Internet as the transportation medium, the request is formatted by the browser using HTTP and sent to the server computer. A moment later, when the server receives the request, it retrieves the file containing the Web page or other information that the client requested, formats it using HTTP, and sends it back to the client over the Internet. Two-tier client/server architecture: Typical request message from a client to a server consists of three major parts: request line, optional request headers, and an optional entity body. This kind architecture has only one client and one server message that a Web client sends to request a file or files from a Web server Three-tier and N-tier client/server architectures: Three-tier architecture extends the two-tier architecture to allow additional processing to occur before the Web server responds to the Web client’s request. Higher-order architectures - that is, those that have more than three tiers - are usually called n-tier architectures. BY: VIKRAM.G.B 2 Lecturer, P.G Dept of Commerce Vivekananda Degree College, Bangalore-55 Operating Systems for Web Servers Most Web servers run on computers that use one of the following operating systems: Microsoft Windows NT Server, Microsoft Windows 2000 or 2003 Server products, Linux, or One of several UNIX-based operating systems, such as Solaris or FreeBSD. Many companies believe that Microsoft server products are simpler for their information systems staff to learn and use than UNIX-based systems. Other companies worry about the security weaknesses caused by the tight integration between application software and the operating system in Microsoft products. UNIX based Web servers are more popular, and many users believe that UNIX is a more secure operating system on which to run a Web server. Web Server Software Computer software, or just software, is any set of machine-readable instructions (most often in the form of a computer program) that directs a computer's processor to perform specific operations. Software is a general term. It can refer to all computer instructions in general or to any specific set of computer instructions. It is inclusive of both machine instructions (the binary code that the processor understands) and source code (more human-understandable instructions that must be rendered into machine code by compilers or interpreters before being executed). Web server software includes a series of complex tools and programs that come together to create and manage a Web server. These tools range from programming language protocols to file transfer protocol programs, which allow programmers to customize their Web servers and provide unique experiences for their users from each of their Web pages. Web server software is used to edit and create Web pages along with various other HTTP formatted files. The most popular Web server programs in use today: Apache HTTP Server, Microsoft Internet Information Server (IIS), and Sun Java System Web Server (JSWS) (often called by its former names, Sun ONE, iPlanet Enterprise Server and Netscape Enterprise Server). Below is the percentage of Websites using different Web Server Software’s:- Apache 62.3%, Microsoft-IIS 16.6%, Nginx 15.7%, LiteSpeed1.9%, Google Servers1.4%, Tomcat 0.7%, Lighttpd 0.5%, IBM Servers 0.4%, Yahoo Traffic Server 0.2%, Oracle Servers 0.2%, Zope 0.1%, Resin0.1%, Zeus0.1% Apache HTTP Server:- The Apache HTTP Server Project is a collaborative software development effort aimed at creating a robust, commercial-grade, feature full and freely-available source code implementation of an HTTP (Web) server. The project is jointly managed by a group of volunteers located around the world, using the Internet and the Web to communicate, plan, and develop the server and its related documentation. This project is part of the Apache Software Foundation. In addition, hundreds of users have contributed ideas, code, and documentation to the project. This file is intended to briefly describe the history of the Apache HTTP Server and recognize the many contributors. In February of 1995, the most popular server software on the Web was the public domain HTTP daemon developed by Rob McCool at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign. However, development of that httpd had stalled after Rob left NCSA in mid-1994, and many webmasters had developed their own extensions and bug fixes that were in need of a common distribution. A small group of these webmasters, contacted via private e-mail, gathered together for the purpose of coordinating their changes (in the form of "patches"). BY: VIKRAM.G.B 3 Lecturer, P.G Dept of Commerce Vivekananda Degree College, Bangalore-55 Using NCSA httpd 1.3 as a base, the group added all of the published bug fixes and worthwhile enhancements we could find, tested the result on our own servers, and made the first official public release (0.6.2) of the Apache server in April 1995. There is a core group of contributors, formed initially of the project founders, and augmented from time to time by other outstanding contributors. There are 'committers', who are granted access to the source code control repositories to help maintain the project or docs, and the core group now managing the project, which is called the Apache HTTP Project Management Committee (PMC, for short). In fact, each Apache Software Foundation project has its own PMC, to determine committers, project direction and overall management.