Ch 22: Web Hosting and Internet Servers

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Ch 22 Web Hosting and Internet Servers

• LaShall Bates

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Web Hosting

• Providing
• Raw web pages (HTML)
• FTP
• SSL
• Streaming audio or video

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Linux vs. Windows hosting???

• Linux provides
• Maintainability and performance
• Multi user, interactive OS
• Multi task Administration
• Can be tuned to be faster

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The Basics

• A web server is a system configured to answer
  HTTP requests. Browsers contact these remote web
  servers and make requests on behalf of users.
• To convert a generic Linux system, install a
  daemon that listens for connections on TCP port
  80, accepts requests for docs and transmits them
  to the requesting user.

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URL

• Uniform Resource Locator, the global address of
  docs and other resources on the WWW.
• 5 parts of the address
• 1. What protocol to use
• 2. IP address or the domain name where the
  resource is located.
• 3. TCP/IP port (opt)
• 4. Directory (opt)
• 5. Filename (case sensitive)

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URL ex.

• An executable file that should be fetched using
  the FTP protocol
• ftp//uark.edu/stuff.exe
• A Web page that should be fetched using the HTTP
  protocol
• http//uark.edu/classes/index.html

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URL Protocols

• http - hypertext transfer protocol (WWW)
• https - secure http (use HTTP/SSL
• ftp - file transfer protocol (FTP)
• news - Usenet news protocol
• javascript - local javascript execution
• file - local files on local computer
• mailto - sends mail to specified e-mail address
• telnet - used to open telnet sessions
• ldap access LDAP directory services

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How HTTP works

• HyperText Transfer Protocol, the underlying
  protocol used by the WWW.
• HTTP defines how messages are formatted and
  transmitted, and what actions Web servers and
  browsers should take in response to various
  commands.
• For example, when you enter a URL in your
  browser, this actually sends an HTTP command to
  the Web server directing it to fetch and transmit
  the requested Web page.

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HTTP Stateless Protocol

• HTTP is called a stateless protocol because each
  command is executed independently, without any
  knowledge of the commands that came before it.
  This is the main reason that it is difficult to
  implement Web sites that react intelligently to
  user input.

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CGI

• The shortcoming of HTTP is being addressed in a
  number of technologies, including CGI, ActiveX,
  Java, JS and cookies.
• CGI is a specification that allows the designer
  to provide active changing web content. It allows
  the HTTP server to exchange info with other
  programs.

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CGI generating on the fly

• CGI scripts can be C(), Perl, Python or any
  other program that can perform real-time I/O

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CGI security

• CGI poses a security problem for Admins. It can
  potentially allow anyone to run a program on your
  server and/or gain access to files.

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Load balancing

• Hits/page views a server can handle.
• Dependent on
• Operating system
• System tuning
• Hardware architecture
• Construction of site
• More important Scalability
• Products spread the work specified by a variety
  of admin-config params such as individual server
  response time and availability

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Choosing a Server

• Robustness
• Performance
• Timeliness of updates and bug fixes
• Availability of source code
• Cost
• Access control and security
• Ability to act as a proxy
• Ability to handle encryption

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Apache

• The August 2002 Netcraft Web Server Survey found
  that 63 of the web sites on the Internet are
  using Apache, thus making it more widely used
  than all other web servers combined.

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Apache

• The name 'Apache' was chosen from respect for the
  Native American Indian tribe of Apache,
  well-known for their superior skills in warfare
  strategy and their inexhaustible endurance.
• Secondarily, and more popularly (though
  incorrectly) accepted, it's a considered cute
  name which stuck. Apache is "A PAtCHy server". It
  was based on some existing code and a series of
  "patch files".

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Installing Apache

• If you want to compile source code yourself
• ./configure prefix/etc/httpd/
• Include or remove features
• enable-module, disable-module
• For a complete list of modules http//httpd.apache
  .org/docs/mod/
• Run make, then make install to compile and
  install appropriate files

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Configuring Apache

• After installation, configure setup
• conf directory (/etc/httpd/conf)
• 3 files to configure
• httpd.conf
• srm.conf
• access.conf

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Apache Conf files httpd

• httpd.conf
• How Apache daemon interacts with system.
• Set TCP port
• location of log files
• various network and performance params
• Configure virtual connections

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Apache Conf files srm

• srm.conf
• Controls resources server needs
• DocumentRoot def defines root of directory tree
  in which servable docs are located.
• Also handling of special URLs (ex.
  http//comp.uark.edu/crane)

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Apache Conf files access

• access.conf
• Security concerns
• Directives that control access on a per-file pr
  per-dir basis, prevents access to sensitive files
  vs. httpd
• Use option ExecCGI in srm.conf to enable CGI
  restrictions
• Allows two access controls one for entire doc dir
  and one for cgi-bin.

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Running Apache

• Start by hand
• /usr/sbin/httpd f /etc/httpd/conf/httpd.conf
• or from rc scripts
• Run at boot time make link in rc directory that
  points to /etc/init.d/httpd file
• Start late in booting sequence after daemons that
  manage functions such as routing and time
  synchronization have started

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High performance Hosting

• TUX is an architecture for kernel-accelerated
  network services.
• Runs in conjunction with Apache
• Serves up static pages without leaving kernel
  space. Minimizes context switches with a
  zero-copy architecture.
• Not recommended for beginners

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Virtual Interfaces

• Allowing the hosting of more than one web site by
  associating more than one IP address with a
  system.
• Allows daemon to identify requests destination
  IP address.
• Single Linux machine responds on the network to
  more IP addresses than it has physical network
  interfaces. Each of the result virtual network
  interfaces can be associated with a corresponding
  domain name that users on the Internet might want
  to connect to.

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Needs of Virtual Interfaces

• Create the virtual interface at TCP/IP level
• ifconfig eth00 128.138.243.150 netmask
  255.255.255.255.192 up
• To make permanent modify startup
• Tell Apache server about virtual interfaces
  created.
• Add VirtualHost clause to httpd.conf file
• One for each virtual interface

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Caching and Proxy Servers

• Squid Internet Object Cache
• Caching and proxy server that runs under Linux
  and supports several protocols
• How it works
• Client browser contacts squid to request object
• Squid makes request on clients behalf (or finds
  cached copy) and returns result to client
• Proxy servers can enhance security or filter
  content

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Anonymous FTP server

• Lets users have accounts to download files you
  have made available.
• Create user--------------------------------
• Create the user ftp in /etc/passwd.
• Misc group, let ftp be root you wish anon. users
  to see.
• Use invalid psw and use shell for better security

ftp400400Anonymous FTP/home/ftp/bin/true
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Anonymous FTP create user dir

• Home directory
• Owned by root, same group as ftp, so Group
  permissions will be for anonymous users
• Set the permissions for ftp to 555 (read,
  nowrite, execute).
• Create subdirs bin, etc, lib, and pub
• Copy ls program to ftp/bin and its shared
  libraries to ftp/lib
• Copy /etc/passwd and group files to ftp/etc
• Should only contain users root, daemon, and ftp
• Replace psw with s

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Anonymous FTP Use

• Put files you want to make available in ftp/pub

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Questions
References http//Apache.org http//webopedia.com
http//squid.nlanr.net/