Web Server Administration

1
Web Server Administration

• Chapter 6
• Configuring a Web Server

2
Overview

• Understand how a Web server works
• Understand HTTP
• Install and configure IIS Web server
• Host multiple Web sites
• Understand virtual directories

3
How a Web Server Works

• HTTP (Hypertext Transfer Protocol) defines how
  information is passed between a browser and a Web
  server
• The two most popular Web servers are
• Apache from Apache Software Foundation
• Internet Information Services (IIS) from
  Microsoft
• Almost two-thirds of all Web servers use Apache

4
How a Web Server Works

• As is true with other servers such as DNS, Web
  servers listen for communication at a port
• The default port is 80
• You can also create Web servers at port numbers
  greater than 1023
• Each Web server has a document root, which is
  where you store the HTML documents

5
Understanding HTTP

• The current version of HTTP is 1.1
• Virtually no browsers are so old that they do not
  support 1.1
• HTTP is a stateless protocol, meaning that each
  Web page sent is independent of every other Web
  page sent
• This makes it more challenging to create a
  shopping cart application

6
HTTP and Cookies

• HTTP Stateless protocol (no connection between
  different requests)
• Web server apps could track information based on
  client IP address, but DHCP makes this
  meaningless
• Cookies Files created on client by Web server
  application that records information from
  previous visits or requests. File name indicates
  server (domain or URL)

7
HTTP/1.0 Retrieving Web Pages

• Establish TCP connection with server (3-step
  handshake SYN SYN/ACK - ACK)
• Client requests a page
• Server sends requested file data
• Server closes connection with client, indicating
  no more data to be transferred
• Client interprets HTML for any embedded file
  reference (graphics, images, sound), repeat this
  process

8
HTTP/1.1 Retrieving Web Pages

• Client identifies support for HTTP/1.1 to server
  when requesting a file
• Persistent Connection is default no need to
  re-establish connection for each embedded file
• Substantial performance improvement since most
  web pages have numerous imbedded files

9
HTTP/1.1 and IIS Performance Features

• Persistent connections Maintain TCP connection
  to send/receive multiple files
• Pipelining Client can send multiple requests in
  parallel rather than handling each request
  sequentially
• Chunked transfers Length of data included in
  transmission so data can be broken into multiple
  pieces of different sizes (benefits ASP)
• Proxy support Caching information provided such
  as expiration dates
• Host headers One IP addr, multiple servers

10
HTTP Request/Response

• URL format host . domain port / path
• Web server port default 80 (443 for SSL
  encrypted data)
• Header indicates type of request (method), URL,
  client HTTP version supported
• Server returns HTTP version, status code, reason
  phrase

11
HTTP Transaction 3 parts

• Request (method) or Response
• Header Section
• Entity Body
• Not relevant to GET method
• Contains data for PUT, POST or server response

12
Understanding HTTP

• When the browser sends a request to a Web server,
  it looks like
• GET /hello.htm HTTP/1.1
• Host www.technowidgets.com
• The above requests the hello.htm file from the
  document root of the Web server
• It specifies the host of www.technowidgets.com
• There could be multiple hosts at the IP address

13
HTTP Request Methods

• Get Retrieve specific URL and imbedded files
• Conditional send data based on modification date
• Partial Retrieve part of the file data
• Head Reply with response headers but no data
  (check validity of a hyperlink or cached data)
• Post Send data to a URL (CGI, ISAPI, ASP)

14
HTTP Headers

• Client Request
• Accept preferred mime types
• Cookie if any from prior visit(s)
• If-Modified-Since conditional
• Referer who provided this address
• User-Agent Browser level

15
HTTP Headers

• Server Response
• Server which software is running
• Set-Cookie leave info for next visit
• Entity Headers
• Content-Length size of data (bytes)
• Content-Type MIME type
• Expires Data will be renewed on expiry
• Last-Modified How old is the data

16
Understanding HTTP

• The following shows some of the headers along
  with the HTML that the Web server would send
• HTTP/1.1 200 OK
• Server Microsoft-IIS/5.0
• Content-Type text/html
• Last-Modified Fri, 17 May 2005 182125 GMT
• Content-Length 43
• lthtmlgtltbodygt
• Hello, World
• lt/bodygtlt/htmlgt
• The headers contain information about the page

17
Status Codes to remember

• 100 Continue
• 200 OK
• 300 series Redirection
• 301 Moved Permanently
• 302 Found (Moved temporarily)
• 304 Not modified (in response to conditional GET
  (If-Modified-Since header)

18
Status Codes to remember

• 400 series Client Error
• 400 Bad request
• 401 Unauthorized login failed
• 403 Execute access forbidden
• 404 File not found
• 500 series Server Error
• 500 Internal server error
• 501 Function not supported
• 502 Bad gateway (invalid response from upstream
  server)

19
Features in Apache

• Apache 1.3 was used for many years but version
  2.0 was released in 2001
• Apache can also be used as a proxy server
• A proxy server isolates your real Web server from
  the Internet
• Apache 2.0 has
• Better support for Windows
• Support for IPv6
• Simplified configuration
• Unicode support in Windows
• Multilanguage error responses
• Apache supports many programming languages such
  as Perl and PHP

20
Features in IIS

• IIS versions associated with Windows versions
• Windows NT IIS 4.0
• Windows 2000 IIS 5.0
• Windows Server 2003 IIS 6.0
• SMTP can be easily added so you can send e-mail
  from your Web pages

21
Features in IIS 5.0

• Web Distributed Authoring and Versioning (WebDAV)
• Allows a server to share Web-based files
• Named virtual hosting
• Multiple Web sites can share a single IP address
• Per Web site bandwidth throttling
• Control bandwidth by Web site
• Kerberos authentication
• Secure Sockets Layer 3.0
• Encrypted communication

22
Features in IIS 6.0

• Increased security
• Default permits only HTML documents
• Expanded language support
• Can use XML and SOAP
• Support for IPv6
• Increased dependability
• Kernel-mode HTTP service
• Self-healing mechanism

23
Components in IIS

• File Transfer Protocol (FTP) server
• To transfer files between user and server
• FrontPage 2000 Server Extensions
• Used by programs to transfer files to and from a
  Web site
• NNTP Service
• Used to create user forums
• SMTP Service
• World Wide Web Server

24
Default Web Site Properties in IIS
25
Tabs on the Default Web Site Properties Dialog Box

• Operators (Windows 2000) only
• This property lists users who can administer Web
  site
• Performance
• Limit bandwidth by Web site
• Limit simultaneous connections (Windows 2003)
• ISAPI Filters
• Specify applications that process HTTP requests

26
Tabs on the Default Web Site Properties Dialog Box

• Home Directory
• Specifies the location and properties of the
  document root
• Log information here
• Permissions
• Documents
• Configure the name for default Web pages
• HTTP Headers
• Add your own custom headers
• Custom Errors
• Create custom pages for HTTP errors

27
Hosting Multiple Web Sitesby Port Number

• Associate each new Web site with a port above
  1023
• To retrieve a Web page from a site at port 8080
• www.technowidgets.com8080/prod.htm
• Because it requires a user to add the port
  number, it is not a popular method

28
Hosting Multiple Web Sitesby IP Address

• You can create multiple IP addresses on a single
  NIC
• Referred to as virtual IP addresses
• Useful for flexibility because if each domain has
  its own unique IP address, you can easily move
  the domain to a different Web server
• It is getting more expensive to get multiple IP
  addresses from an ISP

29
Hosting Multiple Web Sitesby Host Name

• Multiple host names can be associated with a
  single IP address
• Getting a single IP address from your ISP is
  relatively inexpensive
• You can host an almost unlimited number of
  domains with a single IP address
• It is the most common method of hosting

30
Web Server Administration

• Chapter 6
• Configuring a Web Server