Web server


A web server is server software, or hardware dedicated to running this software, that can satisfy client requests on the World Wide Web. A web server can, in general, contain one or more websites. A web server processes incoming network requests over HTTP and several other related protocols.
The primary function of a web server is to store, process and deliver web pages to clients. The communication between client and server takes place using the Hypertext Transfer Protocol. Pages delivered are most frequently HTML documents, which may include images, style sheets and scripts in addition to the text content.
servers are installed together being used for the Wikimedia Foundation.
A user agent, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource or an error message if unable to do so. The resource is typically a real file on the server's secondary storage, but this is not necessarily the case and depends on how the web server is implemented.
While the major function is to serve content, a full implementation of HTTP also includes ways of receiving content from clients. This feature is used for submitting web forms, including uploading of files.
Many generic web servers also support server-side scripting using Active Server Pages, PHP, or other scripting languages. This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this function is used to generate HTML documents dynamically as opposed to returning static documents. The former is primarily used for retrieving or modifying information from databases. The latter is typically much faster and more easily cached but cannot deliver dynamic content.
Web servers can frequently be found embedded in devices such as printers, routers, webcams and serving only a local network. The web server may then be used as a part of a system for monitoring or administering the device in question. This usually means that no additional software has to be installed on the client computer since only a web browser is required.

History

In March 1989 Sir Tim Berners-Lee proposed a new project to his employer CERN, with the goal of easing the exchange of information between scientists by using a hypertext system. The project resulted in Berners-Lee writing two programs in 1990:
Between 1991 and 1994, the simplicity and effectiveness of early technologies used to surf and exchange data through the World Wide Web helped to port them to many different operating systems and spread their use among scientific organizations and universities, and subsequently to the industry.
In 1994 Berners-Lee decided to constitute the World Wide Web Consortium to regulate the further development of the many technologies involved through a standardization process.

Path translation

Web servers are able to map the path component of a Uniform Resource Locator into:
For a static request the URL path specified by the client is relative to the web server's root directory.
Consider the following URL as it would be requested by a client over HTTP:
http://www.example.com/path/file.html
The client's user agent will translate it into a connection to with the following HTTP/2 request:
GET /path/file.html HTTP/2
Host: www.example.com
The web server on will append the given path to the path of its root directory. On an Apache server, this is commonly . The result is the local file system resource:
/home/www/path/file.html
The web server then reads the file, if it exists, and sends a response to the client's web browser. The response will describe the content of the file and contain the file itself or an error message will return saying that the file does not exist or is unavailable.

Kernel-mode and user-mode web servers

A web server can be either incorporated into the OS kernel, or in user space.
Web servers that run in user-mode have to ask the system for permission to use more memory or more CPU resources. Not only do these requests to the kernel take time, but they are not always satisfied because the system reserves resources for its own usage and has the responsibility to share hardware resources with all the other running applications. Executing in user mode can also mean useless buffer copies which are another limitation for user-mode web servers.

Load limits

A web server has defined load limits, because it can handle only a limited number of concurrent client connections per IP address and it can serve only a certain maximum number of depending on:
When a web server is near to or over its limit, it becomes unresponsive.

Causes of overload

At any time web servers can be overloaded due to:
The symptoms of an overloaded web server are:
To partially overcome above average load limits and to prevent overload, most popular web sites use common techniques like:

February 2019

Below are the latest statistics of the market share of all sites of the top web servers on the Internet by W3Techs
.
ProductVendorPercent
ApacheApache44.3%
nginxNGINX, Inc.41.0%
IISMicrosoft8.9%
LiteSpeed Web ServerLiteSpeed Technologies3.9%
GWSGoogle0.9%

All other web servers are used by less than 1% of the websites.

July 2018

Below are the latest statistics of the market share of all sites of the top web servers on the Internet by W3Techs
.
ProductVendorPercent
ApacheApache45.9%
nginxNGINX, Inc.39.0%
IISMicrosoft9.5%
LiteSpeed Web ServerLiteSpeed Technologies3.4%
GWSGoogle1.0%

All other web servers are used by less than 1% of the websites.

February 2017

Below are the latest statistics of the market share of all sites of the top web servers on the Internet by Netcraft
.
ProductVendorJanuary 2017PercentFebruary 2017PercentChangeChart color
IISMicrosoft821,905,28345.66%773,552,45443.16%−2.50
ApacheApache387,211,50321.51%374,297,08020.89%−0.63
nginxNGINX, Inc.317,398,31717.63%348,025,78819.42%1.79
GWSGoogle17,933,7621.00%18,438,7021.03%0.03

February 2016

Below are the latest statistics of the market share of all sites of the top web servers on the Internet by Netcraft
.
ProductVendorJanuary 2016PercentFebruary 2016PercentChangeChart color
ApacheApache304,271,06133.56%306,292,55732.80%0.76
IISMicrosoft262,471,88628.95%278,593,04129.83%0.88
nginxNGINX, Inc.141,443,63015.60%137,459,39116.61%−0.88
GWSGoogle20,799,0872.29%20,640,0582.21%−0.08

Apache, IIS and Nginx are the most used web servers on the World Wide Web.