Chapter 8: Key Concept

WEB SERVER HARDWARE AND SOFTWARE

Key Concept:
This chapter focuses on what happens when a client computer requests a web page. There are different operating systems and different servers that are involved in this process. Web server hardware is important aspect of an online business site.

Web Server Basics
Types of Web Sites:
- Development sites: evaluate different web designs with little initial investment
- Intranets: corporate networks
- Extranets: allow authorized parties outside the company to access certain parts of info stored
- Transaction-processing sites: B2B, available 24/7
- Content-delivery sites: news, histories, summaries, other digital information
Dynamic Content
- dynamic page: content is shaped by program in response to user requests
- static page: unchanging page retrieved from disk
- dynamic content: constructed in response to web clients request
- server-side scripting: programs running on web server create web pages before sending them back to requesting web clients
- dynamic page-generation technologies: active server pages (ASP), JavaServer Pages (JSP), Hypertext preprocessor (PHP)
Various meaning of server
- server: any computer used to provide files or make programs available to other computers connected to it through network
Two-Tier Client/Server Architecture
- messages are created and read only by the client and the server computers
- request message: message that web client sends to request file or files from web server
- request line: contains a comment, name of target resource, protocol name, version number
- request headers: info about types of files that client will accept
- entity body: sometimes used to pass bulk info to server
Three-tier and N-Tier Client/Server Architectures
- allow additional processing to occur before the web server responds to client's request
- third tier often includes databases and related software applications

Software for Web Servers
Operating Systems for Web Servers
- open-source software: developed by community of programmers who make the software available for download at no cost
Web Server Software:
- Apache, Microsoft Internet Information Server (IIS), Sun Java System Web Server

Electronic Mail (E-Mail)
E-mail Benefits: attachments frequently most important part of message
E-mail drawbacks: amount of emails in one day, viruses
Spam: spam is beginning to level off, antispam efforts and software projects help limit the annoyance and cost of spam
Solutions to the Spam Problems:
- individual user antispam tactics
- basic content filtering
- challenge-response content filtering
- advanced content filtering
- legal solutions
- technical solutions

Web Site and Internet Utility Programs
Finger and Ping Utilities:
- finger: program that runs on UNIX operating systems and allows user to obtain some info about other network users
- ping: packet internet groper: tests the connectivity between two computers connected to the internet computers, # of computers
Tracert and Other Route-Tracing Programs
- tracer: sends data packets to every computer on the path between one computer and another computer and clocks the packets round-trip times
Teinet and FTP Utilities:
- teinet: allows users to log on to a computer that is connected to the internet
- telnet protocal: set of rules
- file transfer protocol: part of TCP/IP that defines the formats used to transfer files between TCP/IP connected computers
Link-Checking Utilities: examines each page on site and reports on any URLs that are broken, seem broken, incorrect; orphan file: file on site that is not linked to any page
Remote Server Administration: web site administrator can control web site from any internet-connected computer

Web Server Hardware
Server Computers: have more memory, larger hard disk drives, faster processors, usually more expensive
Web Server Performance Evaluation:
- benchmarking: testing that is used to compare the performance of hardware and software
- throughput: number of HTTP requests that particular hardware and software combo can process in a unit of time
- response time: amount of time a server requires to process one request
Web Server Hardware Architectures
- server farms: large collection of servers
- centralized architecture: use few very large and fast computers
- distributed architecture: decentralized architecture
- load-balancing switch: piece of network hardware that monitors the workloads of servers attached to it and assigns incoming web traffic to the server that has the most available capacity at that instant in time