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  • 1. Internet Engineering Web Servers
  • 2. Introduction
    • Company needs to provide various web services
      • Hosting intranet applications
      • Company web site
      • Various internet applications
    • Therefore there is a need to provide http server
      • First we have a look at what http protocol is
      • Then we talk about Apache web server as leading web server application
  • 3. The World Wide Web (WWW)
    • Global hypertext system
    • Initially developed in 1989
      • By Tim Berners Lee at the European Laboratory for Particle Physics, CERN in Switzerland.
      • To facilitate an easy way of sharing and editing research documents among a geographically dispersed groups of scientists.
    • In 1993, started to grow rapidly
      • Mainly due to the NCSA developing a Web browser called Mosaic (an X Window-based application)
        • First graphical interface to the Web  More convenient browsing
        • Flexible way people can navigate through worldwide resources in the Internet and retrieve them
  • 4. Web Servers
    • Definitions
      • A computer, responsible for accepting HTTP requests from clients, and serving them Web pages.
      • A computer program that provides the above mentioned functionality.
    • Common features
      • Accepting HTTP requests from the network
      • Providing HTTP response to the requester
        • Typically consists of an HTML
      • Usually capable of logging
        • Client requests/Server responses
  • 5. Web Servers cont.
    • Returned content
      • Static
        • Comes from an existing file
      • Dynamic
        • Dynamically generated by some other program/script called by the Web server.
    • Path translation
      • Translate the path component of a URL into a local file system resource
        • Path specified by the client is relative to the server’s root dir
  • 6. HTTP 1.1 servers
    • To comply with HTTP 1.1, servers must:
      • Requiring the Host: Header. Without it server must response with something like below:
        • HTTP/1.1 400 Bad Request
        • Content-Type: text/html
        • Content-Length: 111
        • <html><body> <h2>No Host: header received</h2> HTTP 1.1 requests must include the Host: header. </body></html>
      • Accepting absolute URL’s
        • GET HTTP/1.2
      • Chunked transfer
  • 7. HTTP 1.1 servers (cont.)
    • Persistent Connections and the &quot;Connection: close&quot; Header
    • Using the &quot;100 Continue&quot; Response
    • The Date: Header for caching
    • Handling Requests with If-Modified-Since: or If-Unmodified-Since: Headers
        • HTTP/1.1 304 Not Modified
        • Date: Fri, 31 Dec 1999 23:59:59 GMT
        • [blank line here]
    • Supporting the GET and HEAD methods
    • Supporting HTTP 1.0 Requests
  • 8. First Web Server
    • Berners-Lee wrote two programs
      • A browser called WorldWideWeb
      • The world’s first Web server, which ran on NeXSTEP
        • The machine is on exhibition at CERN’s public museum
  • 9. Most Famous Web Servers
    • Apache HTTP Server from Apache Software Foundation
    • Internet Information Services (IIS) from Microsoft
    • Sun Java Web Server from Sun Microsystems
      • Formerly Sun ONE Web Server, iPlanet Web Server, and Netscape Enterprise Server
    • Zeus Web Server from Zeus Technology
  • 10. Web Servers Usage – Statistics
    • The most popular Web servers, used for public Web sites, are tracked by Netcraft Web Server Survey
      • Details given by Netcraft Web Server Reports
    • Apache is the most popular since April 1996
    • Currently (February 2006) about
      • 66.64%  Apache
      • 25.11%  Microsoft (IIS, PWS, etc.)
      • 0.73%  Zeus
      • 0.67%  Sun (Java Web Server, Netscape Enterprise, iPlanet, …)
  • 11. Web Servers Usage – Statistics cont. Total Sites August 1995 - February 2006 Market Share for Top Servers August 1995 - February 2006 Totals for Active Servers June 2000 - February 2006
  • 12. Apache web server features and functions
    • Caching
    • Content negotiation
      • A resource may be available in several different representations.
      • For example, it might be available in different languages or different media types, or a combination.
      • One way of selecting the most appropriate choice is to give the user an index page, and let them select.
      • However it is often possible for the server to choose automatically by the help of request headers:
        • Accept-Language: fr; q=1.0, en; q=0.5 Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6, image/jpeg; q=0.6, image/*; q=0.5, */*; q=0.1
  • 13. Apache web server features and functions (cont.)
    • Log files
      • In order to effectively manage a web server, it is necessary to get feedback about the activity and performance of the server as well as any problems that may be occurring
      • Error log:
        • [Wed Oct 11 14:32:52 2000] [error] [client] client denied by server configuration: /export/home/live/ap/htdocs/test
      • Access log:
        • Common log format:
          • - frank [10/Oct/2000:13:55:36 -0700] &quot;GET /apache_pb.gif HTTP/1.0&quot; 200 2326
        • Combined log format:
          • - frank [10/Oct/2000:13:55:36 -0700] &quot;GET /apache_pb.gif HTTP/1.0&quot; 200 2326 &quot;; &quot;Mozilla/4.08 [en] (Win98; I ;Nav)&quot;
  • 14. Apache web server features and functions (cont.)
    • Mapping URLs to file system locations:
      • DocumentRoot
      • Alias directive:
        • Alias /docs /var/web
        • the URL will be served from /var/web/dir/file.html.
      • AliasMatch:
        • ScriptAliasMatch ^/~([a-zA-Z0-9]+)/cgi-bin/(.+) /home/$1/cgi-bin/$2
        • will map a request to to the path /home/user/cgi-bin/script.cgi and will treat the resulting file as a CGI script
      • User Directories:
  • 15. Apache web server features and functions (cont.)
    • Mapping URLs to file system locations:
      • URL redirection:
        • Redirect permanent /foo/
      • Reverse proxy:
        • Apache also allows you to bring remote documents into the URL space of the local server.
        • This technique is called reverse proxying because the web server acts like a proxy server by fetching the documents from a remote server and returning them to the client.
        • ProxyPass /foo/
      • Mod_speling for file not found errors
  • 16. Apache web server features and functions (cont.)
    • Access control to filesystem
        • <Directory /> Order Deny,Allow Deny from all </Directory>
        • Directory /usr/users/*/public_html> Order Deny,Allow Allow from all </Directory>
  • 17. Apache web server features and functions (cont.)
    • SSI (Server Side Includes)
      • SSI (Server Side Includes) are directives that are placed in HTML pages, and evaluated on the server while the pages are being served.
      • They let you add dynamically generated content to an existing HTML page, without having to serve the entire page via a CGI program, or other dynamic technology.
      • <!--#config timefmt=&quot;%A %B %d, %Y&quot; --> Today is <!--#echo var=&quot;DATE_LOCAL&quot; -->
      • <!--#include virtual=&quot;/footer.html&quot; -->
      • <!--#include virtual=&quot;/cgi-bin/; -->
  • 18. Apache web server features and functions (cont.)
    • Virtual hosting
      • The term Virtual Host refers to the practice of running more than one web site (such as and on a single machine.
      • Virtual hosts can be &quot; IP-based &quot;, meaning that you have a different IP address for every web site
      • or &quot; name-based &quot;, meaning that you have multiple names running on each IP address. The fact that they are running on the same physical server is not apparent to the end user.
  • 19. Apache web server features and functions (cont.)
    • IP based Virtual hosting
      • the server must have a different IP address for each IP-based virtual host .
      • This can be achieved by the machine having several physical network connections
      • <VirtualHost> ServerAdmin DocumentRoot /groups/smallco/www ServerName ErrorLog /groups/smallco/logs/error_log TransferLog /groups/smallco/logs/access_log </VirtualHost> <VirtualHost> ServerAdmin DocumentRoot /groups/baygroup/www ServerName ErrorLog /groups/baygroup/logs/error_log TransferLog /groups/baygroup/logs/access_log </VirtualHost>
  • 20. Apache web server features and functions (cont.)
    • Name based Virtual hosting
      • HTTP 1.1 compliant clients needed; i.e. Host header should be included in request
      • NameVirtualHost *:80 <VirtualHost *:80> ServerName www.domain.tld ServerAlias domain.tld *.domain.tld DocumentRoot /www/domain </VirtualHost> <VirtualHost *:80> ServerName www.otherdomain.tld DocumentRoot /www/otherdomain </VirtualHost>
  • 21. References
    • TCP/IP Tutorial and Technical Overview, Rodriguez, Gatrell, Karas, Peschke, IBM redbooks, August 2001
    • Wikipedia , the free encyclopedia
    • Apache: The Definitive Guide, 2 nd edition, Ben Laurie, Peter Laurie, O’Reilly, February 1999
    • Webmaster in a nutshell, 1 st edition, Stephen Spainhour, Valerie Quercia, O’Reilly, October 1996
    • Netcraft : February 2006 Web Server Survey