1、Web Server Hardware and SoftwareCHAPTER 8.Learning ObjectivesIn this chapter,you will learn:How a Web server performs its basic functions What operating system and server software is used on Web servers How to identify and manage e-mail and spam control issues How commonly used Internet and Web site
2、 utility programs work What hardware online businesses use to power their Web sites How cloud computing and content delivery networks are providing new Web infrastructure2 2Introduction Case study:Israels Channel 2 News Produces news content and programming for other Channel 2 shows,Web sites and it
3、s mobile device app Web site and mobile app offer many high-resolution photographs and video chips Online news organizations face wide variation in user interest levels and need for Internet bandwidth Breaking news events lead to high demands on the Web site and mobile app and can result in system o
4、verload Peak periods in news business can be unpredictable As a solution,Channel 2 uses Google Cloud Computing to store content3Web Server Basics Client/server architectures used in LANs,WANs,Web Server computers have more memory and larger,faster disk drives than the client computers they serve Web
5、 browser:a type of Web client software Platform neutrality is the ability of a network to connect devices using different operating systems Critical in rapid spread,widespread Web acceptance Web servers main job to respond to Web client requests Main elements:Hardware,operating system software,and W
6、eb server software45FIGURE 8-1 Platform neutrality of the Web Cengage Learning 2017Dynamic Content Generation Static page is an unchanging page retrieved from stored Web server file(s)Dynamic page created in response to user request Customized pages give user an interactive experience Client-side sc
7、ripting software operates on the Web client(browser)and changes Web page display in response to a users actions(JavaScript or Adobe Flash)Server-side scripting program runs on a Web server and creates Web page in response to request for specific information from a Web client6Dynamic Content Generati
8、on(contd.)Software tools to create dynamic Web pages Microsoft ASP.NET,Apache Software Foundation Hypertext Preprocessor(PHP)and Adobe ColdFusion AJAX(asynchronous JavaScript and XML)creates interactive Web sites that look like applications Ruby on Rails,Scala and Python(scripting language)are used
9、to accomplish the same objectives Many Web sites use more than one language and/or development framework to accomplish specific objectives7Multiple Meanings of“Server”Server is any computer providing files or making programs available to other computers connected to it through a network Server softw
10、are makes files and programs available May be part of the operating system(OS)and be referred to as server software(confusing)Some servers connected to Internet via a router Runs Web server software that makes servers files available to other computers and called a Web server E-mail server:handles i
11、ncoming and outgoing e-mail8Multiple Meanings of“Server”(contd.)Database server runs database management software Transaction server runs accounting and inventory management software“Server”describes several types of computer hardware and software Context needed to determine the intended meaning9Web
12、 Client/Server Architectures Web browser requests files from Web server and uses the Internet as the transportation medium Request formatted by browser using HTTP and sent to server computer Server receives request,retrieves requested Web page file,formats using HTTP,and sends back to client over th
13、e Internet Client Web browser software displays page Repeating process of request,response,display Web page with graphics can be slow because each page element requires separate request and response10Web Client/Server Architectures(contd.)Basic model is two-tier client/server architecture One client
14、 and one server computer Request message is the Web client message sent to request file(s)from a Web server that consists of three major parts Request line contains command,target resource name,protocol name,version number Optional request headers contain file type information client accepts Optiona
15、l entity body is used to pass bulk information to server1112FIGURE 8-2 Message flows in a two-tier client/server network Cengage Learning 2017Web Client/Server Architectures(contd.)Server receiving request message executes command included in message Retrieves Web page file from disk and creates a r
16、esponse message to send back to client Identical in structure to request message(slightly different function)Response header line indicates server HTTP version,response status,status information explanation Response header field returns information describing servers attributes Entity body returns H
17、TML page requested by the client machine13Web Client/Server Architectures(contd.)Three-tier architecture allows additional processing before server responds to clients request Often includes databases and related software applications that supply information to the Web server Web server uses softwar
18、e applications output when responding to client requests N-tier architectures have more than three tiers Track customer purchases stored in shopping carts Look up sales tax rates,;keep track of customer preferences,update in-stock inventory databases Keep product catalog current1415FIGURE 8-3 Messag
19、e flows in a three-tier client/server network Cengage Learning 2017Operating Systems for Web Servers Operating system tasks include running programs,allocating computer resources to programs,and proving input and output services Required for a computer to run programs Larger system responsibilities
20、include tracking multiple users,ensuring no interference Web server operating systems software run on Microsoft Windows Server products,Linux or UNIX-based operating systems16Operating Systems for Web Servers(contd.)Some companies consider Microsoft operating system simpler to use than UNIX based sy
21、stems Some concerns about security weaknesses caused by tight integration of Microsoft products Linux is open-source,fast,efficient,easy to install Can be downloaded free from the Web but most companies buy it through a commercial distributor for the additional utilities and support Mandriva,Red Hat
22、,SuSE Linux Enterprise Oracle sells Web server hardware with its UNIX-based operating system Solaris17Web Server Software Commonly used programs are Apache HTTP Server and Microsoft Internet Information Server(IIS)Some businesses,such as Google,wrote their own Apache dominant Web server software sin
23、ce 1996 Free and user-supported with other services available Microsoft IIS bundled with Microsoft Windows Server OS and runs only on Windows systems Used on many intranets,and small and large sites that have adopted Microsoft products as standard ISS is free but OS it comes with can be expensive181
24、9FIGURE 8-4 Percent of active Web sites that use major Web server software productsElectronic Mail(E-Mail)and E-Mail Benefits and Drawback E-mail used to gather information,execute transactions and perform electronic commerce tasks Reason people originally attracted to the Internet Conveys messages
25、in seconds with attachments often the most important message part Most popular form of business communication Drawbacks include the time spent answering e-mails Burdensome and can take 2 hours per day Email attachments can be or contain a computer virus Most frustrating and expensive problem is spam
26、 20Spam and Solutions to the Spam Problem In 2009,the peak year for spam,one 24-hour period showed 220 billion spam e-mail messages sent Spam growth has leveled off and legal and technical solutions will continue to reduce it Benefits reaped by spammers still make it attractive Reducing spam approac
27、hes require passing laws and technical changes in Internet mail-handling systems Approaches under existing laws and technologies require cooperation by organizations Some tactics can be taken by individual e-mail users2122FIGURE 8-5 Spam as a proportion of all business e-mailIndividual User Antispam
28、 Tactics Using a complex e-mail address reduces the chance that a spammer can automatically generate it Downside is that a complex address can be hard to remember Control e-mail address exposure Spammer software robots search for e-mail addresses on discussion boards,in chat rooms,other online sourc
29、es that use email Use multiple e-mail addresses Switch to another if spammers use one Use filtering techniques based on contents23Basic Content Filtering Content-filtering techniques differ in terms of content elements examined,spam indications and how strictly message classification rules applied B
30、asic content filters examine e-mail headers Client-level filtering:individual users computers Server-level filtering:mail server computers Black list spam filter looks for known spammers in incoming messages From addresses White list spam filter looks for good sender From addresses in incoming messa
31、ges High false positives rate24Challenge-Response Content Filtering Compares all incoming messages to a white list If sender is not on the white list,automated e-mail response sent(challenge)Challenge asks sender to reply to e-mail(response)Reply must contain response to a challenge presented in the
32、 e-mail Designed so human can respond easily More information Carnegie Mellon University CAPTCHA Project site Drawback is potential abuse2526FIGURE 8-6 Example of a challenge that uses distorted letters and numbers Cengage Learning 2017Advanced Content Filtering Looks for spam indicators in entire e
33、-mail message Indicator identified:messages spam“score”raised Indicator types are words,word pairs,certain HTML codes,information about where word occurs Spammers stop including defined indicators Bayesian revision statistical technique uses additional knowledge to revise earlier probability estimat
34、es Nave Bayesian filter software allows users to review messages and indicate if message is spam(not spam)Software gradually learns to identify spam and is correct about 95%of the time after training27Legal Solutions January 2004:U.S.CAN-SPAM law went into effect Spam decreased first two months,but
35、returned to previous levels after no threat of federal prosecution Prohibits misleading e-mail message address header information,deceptive subject headers and transfer of email addresses Some spammers have been prosecuted,fined and received jail time Many use servers outside U.S.(jurisdiction issue
36、s)Legal solutions have had only limited success Expensive to prosecute spammers28Technical Solutions Internet design did not include mechanisms ensuring e-mail sender identity would be know to recipient Internets communication protocol designed to be a polite set of rules where a sending computer wa
37、its for acknowledgement that message was received Originating computer will slow if acknowledgement is delayed(must continue to scan for it)and will not send more messages until acknowledgment received Defending(receiving)company must develop way to identify computers sending spam and delay acknowle
38、dgement29Technical Solutions(contd.)Computer being spammed can also launch a return attack called teergrubing(“tar pit”)Send e-mail messages back to suspected spamming computer with the objective of setting a trap that drags down its ability to send spam Concern is that counterattack might violate l
39、aws Ultimate spam solution could come from new e-mail protocols providing absolute verification of e-mail message source Currently most effective solutions have been coordinated efforts to identify and block spammers30Web Site Utility Programs TCP/IP supports utility programs(tools)Run on Web server
40、 or client computers E-mail:earliest Internet utility program Most important utility Key element in electronic commerce strategies31Tracert and Other Route-Tracing Programs Tracert(TRACE RouTe)sends data packets to every computer on path between one computer and another and clocks packets round-trip
41、 times Provides indication of time message needs to travel from one computer to another and back Ensures remote computer online and pinpoints data traffic congestion Calculates and displays the number of hops between computers and time to traverse entire one-way path3233FIGURE 8-7 Tracing a path bet
42、ween two computers on the Internet Cengage Learning 2017Telnet and FTP Utilities andIndexing and Searching Utility Programs Telnet program allows a person using one computer to access files and run programs on a second computer connected to the Internet File Transfer Protocol(FTP)is the part of the
43、TCP/IP rules that defines formats used to transfer files between TCP/IP connected computers Search engines and indexing programs are important elements of many Web servers When a browser requests a Web site search,engine compares index terms to the requesters search terms to find matching documents3
44、4Data Analysis Software Web servers capture visitor information and places it into a Web log file(grows quickly)Third-party Web log file analysis programs summarize information in the file Query log file and return gross summary information or accumulating details Popular Web log file analysis progr
45、ams Adobe Analytics,Google Analytics,WebTrends35Link-Checking Utilities Dead link displays an error message rather than Web page when clicked Sites with many dead links are said to have link rot Link checker utility examines each site page and reports URLs that no longer exists Identifies orphan fil
46、es which are files on Web server not linked to a page Also includes script checking and HTML validation Adobe Dreamweaver includes link-checking program Free standing link-checking programs include Elsop LinkScan and LinxCop36Remote Server Administration Web site administrator controls Web site from
47、 any Internet connected computers Monitor server activity and manipulate server from wherever administrator happens to be LabTech Software includes remote administration,link-checking,HTML troubleshooting,site-monitoring and other utility programs Useful in managing the operations on the Web37Web Se
48、rver Hardware Wide variety of computer brands,types,sizes used by organizations to host online operations Small companies run Web sites on desktop PCs Most online business operations are operated on computers designed for site hosting Businesses select specific hardware and software elements based o
49、n sites functionality,expected visitors,number and size of pages and graphics38Server Computers Generally have more memory,larger(faster)hard disk drives and faster processors than typical desktop computers Many Web server computers use multiple processors Most companies spend$2,000-$50,000 on an in
50、dividual Web server with large organizations spending millions on server hardware May be housed in freestanding cases but most are installed in equipment racks Blade servers are servers-on-a-card Small in size:300 installed in single 6-foot rack3940FIGURE 8-8 Rack-mounted blade serversWeb Servers an
