5-WebServers.ppt

Internet Engineering
Web Servers

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

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

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

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

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://www.somehost.com/path/file.html HTTP/1.2
 Chunked transfer

HTTP 1.1 servers (cont.)
 Persistent Connections and the "Connection: close"
Header
 Using the "100 Continue" 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

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

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

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, …)

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

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

(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 127.0.0.1] client denied by
server configuration: /export/home/live/ap/htdocs/test
 Access log:
 Common log format:
 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET /apache_pb.gif
HTTP/1.0" 200 2326
 Combined log format:
 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET /apache_pb.gif
HTTP/1.0" 200 2326 "http://www.example.com/start.html" "Mozilla/4.08
[en] (Win98; I ;Nav)"

(cont.)
 Mapping URLs to file system locations:
 DocumentRoot
 Alias directive:
 Alias /docs /var/web
 the URL http://www.example.com/docs/dir/file.html 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 http://example.com/~user/cgi-
bin/script.cgi to the path /home/user/cgi-bin/script.cgi and will
treat the resulting file as a CGI script
 User Directories:
 http://www.example.com/~user/file.html

(cont.)
 Mapping URLs to file system locations:
 URL redirection:
 Redirect permanent /foo/ http://www.example.com/bar/
 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/ http://internal.example.com/bar/
 Mod_speling for file not found errors

(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>

(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.
 
Today is 
 


(cont.)
 Virtual hosting
 The term Virtual Host refers to the practice of running more
than one web site (such as www.company1.com and
www.company2.com) on a single machine.
 Virtual hosts can be "IP-based", meaning that you have a
different IP address for every web site
 or "name-based", 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.

(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 www.smallco.com>
ServerAdmin webmaster@mail.smallco.com
DocumentRoot /groups/smallco/www
ServerName www.smallco.com
ErrorLog /groups/smallco/logs/error_log
TransferLog /groups/smallco/logs/access_log
</VirtualHost>
<VirtualHost www.baygroup.org>
ServerAdmin webmaster@mail.baygroup.org
DocumentRoot /groups/baygroup/www
ServerName www.baygroup.org
ErrorLog /groups/baygroup/logs/error_log
TransferLog /groups/baygroup/logs/access_log
</VirtualHost>

(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>

References
 http://www.jmarshall.com/easy/http/
 TCP/IP Tutorial and Technical Overview, Rodriguez,
Gatrell, Karas, Peschke, IBM redbooks, August 2001
 Wikipedia, the free encyclopedia
 Apache: The Definitive Guide, 2nd
edition, Ben Laurie,
Peter Laurie, O’Reilly, February 1999
 Webmaster in a nutshell, 1st
edition, Stephen Spainhour,
Valerie Quercia, O’Reilly, October 1996
 Netcraft: February 2006 Web Server Survey

5-WebServers.ppt

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