Web server

The term web server can mean one of two things: # A computer that is responsible for accepting HTTP requests from clients, which are known as web browsers, and serving them web pages, which are usually HTML documents. # A computer program that provides the functionality described in the first sense of the term.

=Common features=

Although web server programs differ in detail, they all share some basic common features.

Every web server program operates by accepting HTTP requests from the network, and providing an HTTP response to the requester. The HTTP response typically consists of an HTML document, but can also be a raw text file, an image, or some other type of document.

Usually web servers have also the capability of Data logging some detailed information, about client requests and server responses, to Server log; this allows the Web master to collect statistics by running Web log analysis software on log files.

=Origin of returned content=

The origin of the content sent by server is called static if it comes from an existing Computer file or dynamic if it is dynamically generated by some other program or Scripting programming language called by web server. Usually serving static content is somewhat much faster than serving dynamic content.

=Path translation=

Web servers usually translate the path component of a Uniform Resource Locator (URL) into a local file system resource. The URL path specified by the client is relative to the web server s root directory.

Consider the following URI as it would be requested by a client:

http://www.example.com/path/file.html

The client s web browser will translate it into a connection to www.example.com with the following HTTP 1.1 request:

GET /path/file.html HTTP/1.1 Host: www.example.com

The web server on www.example.com will append the given path to the path of its root directory. On Unix machines, this is commonly /var/www/htdocs. The result is the local file system resource:

/var/www/htdocs/path/file.html

The web server will then read the file, if it exists, and send a response to the client s web browser. The response will describe the content of the file and contain the file itself.

=Load Limits=

Each web server can handle a limited number of concurrent client connections (usually between 2 and 60000) and it can serve only a certain maximum number of requests per second depending on its own settings, the HTTP request type and the hardware and software limits of the Operating system where it is working.

To partially overcome these limits, most popular web sites use common techniques like:

using different URLs to serve

static content (i.e. http://images.example.com) and dynamic content (i.e. http://www.example.com) by separate web servers;

using many web servers that are grouped together so that they act or are seen as one big web server, see also: Load balancer.

The symptoms of an overloaded web server are:

requests are served with noticeably (long) delays (from 1 second to a few hundreds of seconds);

List of HTTP status codes are returned to clients (sometimes also unrelated 404 error may be returned);

TCP connections are refused or reset before any content is sent to clients.

=Historical note=

In . Today, this machine is on exhibition for all to see at CERN s public museum, [http://microcosm.web.cern.ch/Microcosm/ Microcosm].

=Software=

The four top most common web or HTTP server programs are:

Apache HTTP Server from the Apache Software Foundation.

Internet Information Services (IIS) from Microsoft.

Sun Java System Web Server from Sun Microsystems, formerly Sun ONE Web Server, iPlanet Web Server, and Netscape Enterprise Server.

Zeus Web Server from [http://www.zeus.com/ Zeus Technology].

There are thousands of different web server programs available, many of them are specialized for some uses and can be tailored to satisfy specific needs.

See for a comprehensive list of HTTP server programs.

=Statistics=

The most popular web servers, used for public web sites, are tracked by [http://news.netcraft.com/archives/web_server_survey.html Netcraft Web Server Survey], with details given by [http://survey.netcraft.com/Reports/ Netcraft Web Server Reports].

=See also=

*HTTP, HTTPS *Tiny web servers *Common Gateway Interface, FastCGI, ASP, PHP *Virtual hosting *LAMP_(software bundle) *Web browser *Web log analysis software *List of Web servers

=External links=

*RFC 2616, the Request for Comments document that defines the HTTP 1.1 protocol.