Internet Engineering Web Servers Introduction n Company

Internet Engineering Web Servers

Introduction n Company needs to provide various web services q q q n Hosting intranet applications Company web site Various internet applications Therefore there is a need to provide http server q q 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) n n n Global hypertext system Initially developed in 1989 q By Tim Berners Lee at the European Laboratory for Particle Physics, CERN in Switzerland. q To facilitate an easy way of sharing and editing research documents among a geographically dispersed groups of scientists. In 1993, started to grow rapidly q Mainly due to the NCSA developing a Web browser called Mosaic (an X Window-based application) n n First graphical interface to the Web More convenient browsing Flexible way people can navigate through worldwide resources in the Internet and retrieve them

Web Browsers n n Provides access to a Web server Basic components q q n HTML interpreter HTTP client used to retrieve HTML pages Some also support q FTP, NTTP, POP, SMTP, …

Web Servers n Definitions q q n 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 q q Accepting HTTP requests from the network Providing HTTP response to the requester n q Typically consists of an HTML Usually capable of logging n Client requests/Server responses

Web Servers cont. n Returned content q Static n q Dynamic n n Comes from an existing file Dynamically generated by some other program/script called by the Web server. Path translation q Translate the path component of a URL into a local file system resource n Path specified by the client is relative to the server’s root dir

http protocol n n Created to define the communication between a web server and a client It's the network protocol used to deliver virtually all files and other data (collectively called resources) on the World Wide Web A browser is an HTTP client because it sends requests to an HTTP server (Web server), which then sends responses back to the client. The standard (and default) port for HTTP servers to listen on is 80, though they can use any port.

Structure of http transactions n n Like most network protocols, HTTP uses the client-server model: An HTTP client opens a connection and sends a request message to an HTTP server; the server then returns a response message, usually containing the resource that was requested Format of a http message: <initial line, different for request vs. response> Header 1: value 1 Header 2: value 2 Header 3: value 3 <optional message body goes here, like file contents or query data; it can be many lines long, or even binary data >

Initial line n n A typical initial request line: q GET /path/to/file/index. html HTTP/1. 0 Initial response line: q HTTP/1. 0 200 OK q HTTP/1. 0 404 Not Found Status code: q 1 xx indicates an informational message only q 2 xx indicates success of some kind q 3 xx redirects the client to another URL q 4 xx indicates an error on the client's part q 5 xx indicates an error on the server's part Common status codes: q 200 OK q 404 Not Found q 301 Moved Permanently q 302 Moved Temporarily q 303 See Other (HTTP 1. 1 only) q 500 Server Error

Header lines n Typical request headers: q q n From: email address of requester User-Agent: for example User-agent: Mozilla/3. 0 Gold Typical response headers: q q Server: for example Server: Apache/1. 2 b 3 -dev Last-modified: fro example Last-Modified: , 19 Feb 2006 23: 59 GMT

Message body n n n In a response, this is where the requested resource is returned to the client (the most common use of the message body), or perhaps explanatory text if there's an error. In a request, this is where user-entered data or uploaded files are sent to the server. If an HTTP message includes a body, there are usually header lines in the message that describe the body. In particular, q q The Content-Type: header gives the MIME-type of the data in the body, such as text/html or image/gif. The Content-Length: header gives the number of bytes in the body.

Sample HTTP exchange n n n To retrieve the file at the URL http: //www. somehost. com/path/file. html Request: GET /path/file. html HTTP/1. 0 From: someuser@jmarshall. com User-Agent: HTTPTool/1. 0 [blank line here] Response: HTTP/1. 0 200 OK Date: Fri, 31 Dec 1999 23: 59 GMT Content-Type: text/html Content-Length: 1354 <html> <body> <h 1>Happy New Millennium!</h 1> (more file contents). . . </body> </html>

HTTP methods n n n GET: request a resource by url HEAD q is just like a GET request, except it asks the server to return the response headers only, and not the actual resource (i. e. no message body). q This is useful to check characteristics of a resource without actually downloading it, thus saving bandwidth. POST q A POST request is used to send data to the server to be processed in some way, like by a CGI script. q There's a block of data sent with the request, in the message body. There are usually extra headers to describe this message body, like Content-Type: and Content-Length: . q The request URI is not a resource to retrieve; it's usually a program to handle the data you're sending. q The HTTP response is normally program output, not a static file.

HTTP 1. 1 n It is a superset of HTTP 1. 0. Improvements include: q q Faster response, by allowing multiple transactions to take place over a single persistent connection. Faster response and great bandwidth savings, by adding cache support. Faster response for dynamically-generated pages, by supporting chunked encoding, which allows a response to be sent before its total length is known. Efficient use of IP addresses, by allowing multiple domains to be served from a single IP address.

HTTP 1. 1 clients n To comply with HTTP 1. 1, clients must q Include Host: header with each request : GET /path/file. html HTTP/1. 1 Host: www. host 1. com: 80 [blank line here] q Accept response with chunked data: HTTP/1. 1 200 OK Date: Fri, 31 Dec 1999 23: 59 GMT Content-Type: text/plain Transfer-Encoding: chunked 1 a; ignore-stuff-here abcdefghijklmnopqrstuvwxyz 10 1234567890 abcdef 0 some-footer: some-value another-footer: another-value [blank line here]

HTTP 1. 1 clients (cont. ) n n Either support persistent connections or include the “Connection: close” header with each request Handle the “ 100 continue” response HTTP/1. 1 100 Continue HTTP/1. 1 200 OK Date: Fri, 31 Dec 1999 23: 59 GMT Content-Type: text/plain Content-Length: 42 some-footer: some-value another-footer: another-value abcdefghijklmnoprstuvwxyz 1234567890 abcdef

HTTP 1. 1 servers n To comply with HTTP 1. 1, servers must: q 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> <h 2>No Host: header received</h 2> HTTP 1. 1 requests must include the Host: header. </body></html> q Accepting absolute URL’s n q GET http: //www. somehost. com/path/file. html HTTP/1. 2 Chunked transfer

HTTP 1. 1 servers (cont. ) n n 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 GMT [blank line here] n n Supporting the GET and HEAD methods Supporting HTTP 1. 0 Requests

First Web Server n Berners-Lee wrote two programs q q A browser called World. Wide. Web The world’s first Web server, which ran on Ne. XSTEP n The machine is on exhibition at CERN’s public museum

Most Famous Web Servers n n n Apache HTTP Server from Apache Software Foundation Internet Information Services (IIS) from Microsoft Sun Java Web Server from Sun Microsystems q n Formerly Sun ONE Web Server, i. Planet Web Server, and Netscape Enterprise Server Zeus Web Server from Zeus Technology

Web Servers Usage – Statistics n The most popular Web servers, used for public Web sites, are tracked by Netcraft Web Server Survey q n n Details given by Netcraft Web Server Reports Apache is the most popular since April 1996 Currently (February 2006) about q q 66. 64% Apache 25. 11% Microsoft (IIS, PWS, etc. ) 0. 73% Zeus 0. 67% Sun (Java Web Server, Netscape Enterprise, i. Planet, …)

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 n n Caching Content negotiation q q 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

Apache web server features and functions (cont. ) n n DSO (Dynamic Shared Object) mechanism Log files q 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 q Error log: n q [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: n Common log format: q n 127. 0. 0. 1 - frank [10/Oct/2000: 13: 55: 36 -0700] "GET /apache_pb. gif HTTP/1. 0" 200 2326 Combined log format: q 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] (Win 98; I ; Nav)"

Apache web server features and functions (cont. ) n Mapping URLs to file system locations: q q Document. Root Alias directive: n n q Alias. Match: n n q Alias /docs /var/web the URL http: //www. example. com/docs/dir/file. html will be served from /var/web/dir/file. html. Script. Alias. Match ^/~([a-z. A-Z 0 -9]+)/cgi-bin/(. +) /home/$1/cgibin/$2 will map a request to http: //example. com/~user/cgibin/script. cgi to the path /home/user/cgi-bin/script. cgi and will treat the resulting file as a CGI script User Directories: n http: //www. example. com/~user/file. html

Apache web server features and functions (cont. ) n Mapping URLs to file system locations: q URL redirection: n q Reverse proxy: n n n q Redirect permanent /foo/ http: //www. example. com/bar/ 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. Proxy. Pass /foo/ http: //internal. example. com/bar/ Mod_speling for file not found errors

Apache web server features and functions (cont. ) n Access control to filesystem n n <Directory /> Order Deny, Allow Deny from all </Directory> Directory /usr/users/*/public_html> Order Deny, Allow from all </Directory>

Apache web server features and functions (cont. ) n SSI (Server Side Includes) q q q 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

Apache web server features and functions (cont. ) n Virtual hosting q q q The term Virtual Host refers to the practice of running more than one web site (such as www. company 1. com and www. company 2. 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.

Apache web server features and functions (cont. ) n IP based Virtual hosting q the server must have a different IP address for each IP-based virtual host. q This can be achieved by the machine having several physical network connections q <Virtual. Host www. smallco. com> Server. Admin webmaster@mail. smallco. com Document. Root /groups/smallco/www Server. Name www. smallco. com Error. Log /groups/smallco/logs/error_log Transfer. Log /groups/smallco/logs/access_log </Virtual. Host> <Virtual. Host www. baygroup. org> Server. Admin webmaster@mail. baygroup. org Document. Root /groups/baygroup/www Server. Name www. baygroup. org Error. Log /groups/baygroup/logs/error_log Transfer. Log /groups/baygroup/logs/access_log </Virtual. Host>

Apache web server features and functions (cont. ) n Name based Virtual hosting q HTTP 1. 1 compliant clients needed; i. e. Host header should be included in request q Name. Virtual. Host *: 80 <Virtual. Host *: 80> Server. Name www. domain. tld Server. Alias domain. tld *. domain. tld Document. Root /www/domain </Virtual. Host> <Virtual. Host *: 80> Server. Name www. otherdomain. tld Document. Root /www/otherdomain </Virtual. Host>

References n n n 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, 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