The inside/front of a Dell PowerEdge web server

The term web server can mean one of two things:

1. A computer program that is responsible for accepting HTTP requests from web clients, which are known as web browsers, and serving them HTTP responses along with optional data contents, which usually are web pages such as HTML documents and linked objects (images, etc. The multinational technology company Dell Inc develops manufactures sells and supports Personal computers and other computer-related products Dell Inc gives the moniker PowerEdge (PE to its server product line which As of 2007 brought in approximately 15% of Dell's overall revenue from Computer programs (also software programs, or just programs) are instructions for a Computer. Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. The World Wide Web (commonly shortened to the Web) is a system of interlinked Hypertext documents accessed via the Internet. A web browser is a software application which enables a user to display and interact with text images videos music games and other information typically located on a A server is a Computer dedicated to providing one or more services over a computer network typically through a request-response routine HTML, an initialism of HyperText Markup Language, is the predominant Markup language for Web pages It provides a means to describe the structure ).
2. A computer that runs a computer program as described above. A computer is a Machine that manipulates data according to a list of instructions.

Common features

The rack of web servers hosting the My Opera Community site on the Internet. My Opera Community is the support community for the Opera web browser The My Opera Community rack, as seen to the left. My Opera Community is the support community for the Opera web browser From the top, user file storage (content of files. myopera. com), "bigma" (the master MySQL database server), and two IBM blade centers containing multi-purpose machines (Apache front ends, Apache back ends, slave MySQL database servers, load balancers, file servers, cache servers and sync masters. MySQL is a Relational database management system (RDBMS which has more than 11 million installations A Computer Database is a structured collection of records or data that is stored in a computer system In Computer networking, load balancing is a technique to spread work between two or more computers network links CPUs hard drives or other resources in order to get optimal In Computing, a file server is a computer attached to a network that has the primary purpose of providing a location for the shared storage of Computer files (such

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

1. HTTP: every web server program operates by accepting HTTP requests from the client, and providing an HTTP response to the client. Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. The HTTP response usually consists of an HTML document, but can also be a raw file, an image, or some other type of document (defined by MIME-types). HTML, an initialism of HyperText Markup Language, is the predominant Markup language for Web pages It provides a means to describe the structure Multipurpose Internet Mail Extensions ( MIME) is an Internet standard that extends the format of e-mail to support text in Character If some error is found in client request or while trying to serve it, a web server has to send an error response which may include some custom HTML or text messages to better explain the problem to end users.
2. Logging: usually web servers have also the capability of logging some detailed information, about client requests and server responses, to log files; this allows the webmaster to collect statistics by running log analyzers on log files. Data logging is the practice of recording sequential Data, often chronologically. Data logging is the practice of recording sequential Data, often chronologically. A server log is a log file (or several files automatically created and maintained by a server of activity performed by it The webmaster (feminine webmistress) also called the Web architect, the Web developer, the site author, or the website Web log analysis software (also called a web log analyzer) is a simple kind of Web analytics software that parses a log file from a Web server

In practice many web servers implement the following features also:

1. Authentication, optional authorization request (request of user name and password) before allowing access to some or all kind of resources. Authentication (from Greek αυθεντικός real or genuine from authentes author is the act of establishing or confirming something (or someone as Users in a Computing context refers to one who uses a computer system In computing a password is a Word or string of characters that is entered often along with a user name, in modern times usually into a computer system
2. Handling of static content (file content recorded in server's filesystem(s)) and dynamic content by supporting one or more related interfaces (SSI, CGI, SCGI, FastCGI, JSP, PHP, ASP, ASP .NET, Server API such as NSAPI, ISAPI, etc. A static Web page is a Web page that always comprises the same information in response to all download requests from all users In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make Classical Hypertext navigation occurs among Server Side Includes (SSI is a simple Server-side scripting language used almost exclusively for the web. The Common Gateway Interface ( CGI) is a standard protocol for interfacing external Application software with an information server The Simple Common Gateway Interface ( SCGI) is a protocol for applications to interface with HTTP servers an alternative to the CGI protocol JavaServer Pages ( JSP) is a Java technology that allows Software developers to dynamically generate HTML, XML or other types of documents PHP is a computer Scripting language. Originally designed for producing Dynamic web pages it has evolved to include a Command line interface capability Active Server Pages ( ASP) is Microsoft 's first server-side script engine for dynamically-generated web pages ASPNET is a Web application framework developed and marketed by Microsoft, that Programmers can use to build dynamic Web sites Web applications In Computer science, the Server Application Programming Interface (SAPI is the generic term used to designate direct module interfaces to Web server applications The Internet Server Application Programming Interface ( ISAPI) is an N-tier API of Internet Information Services (IIS Microsoft 's ).
3. HTTPS support (by SSL or TLS) to allow secure (encrypted) connections to the server on the standard port 443 instead of usual port 80. Transport Layer Security ( TLS) and its predecessor Secure Sockets Layer ( SSL) are Cryptographic protocols that provide secure Transport Layer Security ( TLS) and its predecessor Secure Sockets Layer ( SSL) are Cryptographic protocols that provide secure The Transmission Control Protocol ( TCP) and the User Datagram Protocol ( UDP) are Transport Layer protocols of the Internet Protocol
4. Content compression (i. e. by gzip encoding) to reduce the size of the responses (to lower bandwidth usage, etc. gzip is a Software application used for File compression. gzip is short for GNU zip; the program is a Free software replacement for the ).
5. Virtual hosting to serve many web sites using one IP address. "vhost" redirects here for vhosts in relation to Internet Relay Chat see Vhost (IRC Virtual hosting is a method that servers An Internet Protocol ( IP) address is a numerical identification ( Logical address) that is assigned to devices participating in a Computer network
6. Large file support to be able to serve files whose size is greater than 2 GB on 32 bit OS. Large file support, often abbreviated to LFS, is the term frequently applied to the ability to create files larger than 2 GiB on 32-bit Operating systems An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination
7. Bandwidth throttling to limit the speed of responses in order to not saturate the network and to be able to serve more clients. Bandwidth throttling is a method of ensuring a bandwidth intensive device such as a server, will limit ("throttle" the quantity of data it transmits and/or

Origin of returned content

The origin of the content sent by server is called:

• static if it comes from an existing file lying on a filesystem;
• dynamic if it is dynamically generated by some other program or script or Application Programming Interface called by the web server. A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make Classical Hypertext navigation occurs among "Scripting" redirects here For other uses see Script.

Serving static content is usually much faster (from 2 to 100 times) than serving dynamic content, especially if the latter involves data pulled from a database. A Computer Database is a structured collection of records or data that is stored in a computer system

Path translation

Web servers are able to map the path component of a Uniform Resource Locator (URL) into:

• a local file system resource (for static requests);
• an internal or external program name (for dynamic requests). Uniform Resource Locator is an URI which also specifies where the identified resource is available and the protocol for retrieving it In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make

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:

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. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer 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

A web server (program) has defined load limits, because it can handle only a limited number of concurrent client connections (usually between 2 and 60,000, by default between 500 and 1,000) per IP address (and IP port) and it can serve only a certain maximum number of requests per second depending on:

• its own settings;
• the HTTP request type;
• content origin (static or dynamic);
• the fact that the served content is or is not cached;
• the hardware and software limits of the OS where it is working. An Internet Protocol ( IP) address is a numerical identification ( Logical address) that is assigned to devices participating in a Computer network Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. In Computer science, a cache (kæʃ like "cash") is a collection of data duplicating original Typical PC hardware A typical Personal computer consists of a case or chassis in a tower shape (desktop and the following parts Motherboard An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination

When a web server is near to or over its limits, it becomes overloaded and thus unresponsive.

Overload causes

A daily graph of a web server's load, indicating a spike in the load early in the day.

At any time web servers can be overloaded because of:

• Too much legitimate web traffic (i. e. thousands or even millions of clients hitting the web site in a short interval of time. e. g. Slashdot effect);
• DDoS (Distributed Denial of Service) attacks;
• Computer worms that sometimes cause abnormal traffic because of millions of infected computers (not coordinated among them);
• XSS viruses can cause high traffic because of millions of infected browsers and/or web servers;
• Internet web robots traffic not filtered / limited on large web sites with very few resources (bandwidth, etc. The Slashdot effect, also known as slashdotting, is the phenomenon of a popular Website linking to a smaller site causing the smaller site to slow down or even temporarily A computer worm is a self-replicating Computer program. It uses a network to send copies of itself to other nodes (computer terminals on the network and it may do so without A computer virus is a Computer program that can copy itself and infect a computer without permission or knowledge of the user The term web server can mean one of two things A Computer program that is responsible for accepting HTTP requests from web clients which are Internet bots, also known as web robots, WWW robots or simply bots, are software applications that run automated tasks over the Internet );
• Internet (network) slowdowns, so that client requests are served more slowly and the number of connections increases so much that server limits are reached;
• Web servers (computers) partial unavailability, this can happen because of required / urgent maintenance or upgrade, HW or SW failures, back-end (i. The Internet is a global system of interconnected Computer networks A computer is a Machine that manipulates data according to a list of instructions. Typical PC hardware A typical Personal computer consists of a case or chassis in a tower shape (desktop and the following parts Motherboard Front-end and back-end are generalized terms that refer to the initial and the end stages of a process e. DB) failures, etc. A Computer Database is a structured collection of records or data that is stored in a computer system ; in these cases the remaining web servers get too much traffic and become overloaded.

Overload symptoms

The symptoms of an overloaded web server are:

• requests are served with (possibly long) delays (from 1 second to a few hundred seconds);
• 500, 502, 503, 504 HTTP errors are returned to clients (sometimes also unrelated 404 error or even 408 error may be returned);
• TCP connections are refused or reset (interrupted) before any content is sent to clients;
• in very rare cases, only partial contents are sent (but this behavior may well be considered a bug, even if it usually depends on unavailable system resources). The following is a list of HTTP response status codes and standard associated phrases intended to give a short textual description of the status The 404 or Not Found Error message is an HTTP standard response code indicating that the client was able to communicate with the server The following is a list of HTTP response status codes and standard associated phrases intended to give a short textual description of the status The Transmission Control Protocol (TCP is one of the core protocols of the Internet Protocol Suite. A software bug (or just “bug” is an error flaw mistake Failure, fault or “undocumented feature” in a Computer program that prevents it

lee

Anti-overload techniques

To partially overcome above load limits and to prevent overload, most popular web sites use common techniques like:

• managing network traffic, by using:
  • Firewalls to block unwanted traffic coming from bad IP sources or having bad patterns;
  • HTTP traffic managers to drop, redirect or rewrite requests having bad HTTP patterns;
  • Bandwidth management and traffic shaping, in order to smooth down peaks in network usage;
• deploying web cache techniques;
• using different domain names to serve different (static and dynamic) content by separate Web servers, i. A firewall is an integrated collection of security measures designed to prevent unauthorized electronic access to a networked computer system Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. In Computer networking, bandwidth management is the process of measuring and controlling the communications (traffic packets on a network link to avoid filling the link to Traffic shaping (also known as "packet shaping" is the control of Computer network traffic in order to optimize or guarantee performance lower latency, Web caching is the caching of Web documents (eg HTML pages, images) in order to reduce bandwidth usage server load In Computer networking, a domain name is a name given to a collection of network devices that belong to a domain which is an administrative space managed according e. :

  • http://images. example. com
    

  • http://www. example. com
    

• using different domain names and/or computers to separate big files from small and medium sized files; the idea is to be able to fully cache small and medium sized files and to efficiently serve big or huge (over 10 - 1000 MB) files by using different settings;
• using many Web servers (programs) per computer, each one bound to its own network card and IP address;
• using many Web servers (computers) that are grouped together so that they act or are seen as one big Web server, see also: Load balancer;
• adding more hardware resources (i. In Computer science, a cache (kæʃ like "cash") is a collection of data duplicating original A Network card, Network Adapter, LAN Adapter or NIC (network interface card is a piece of Computer hardware designed to allow computers An Internet Protocol ( IP) address is a numerical identification ( Logical address) that is assigned to devices participating in a Computer network In Computer networking, load balancing is a technique to spread work between two or more computers network links CPUs hard drives or other resources in order to get optimal e. RAM, disks) to each computer;
• tuning OS parameters for hardware capabilities and usage;
• using more efficient computer programs for web servers, etc. Disk storage is a general category of a Computer storage mechanisms in which data is recorded on planar round and rotating surfaces ( disks, discs, or Computer programs (also software programs, or just programs) are instructions for a Computer. ;
• using other workarounds, especially if dynamic content is involved. A workaround is a bypass of a recognized problem in a system A workaround is typically a temporary fix that implies that a genuine solution to the problem is needed

Historical notes

The world's first web server.

In 1989 Tim Berners-Lee proposed to his employer CERN (European Organization for Nuclear Research) a new project, which had the goal of easing the exchange of information between scientists by using a hypertext system. Sir Timothy John Berners-Lee OM KBE FRS FREng FRSA (born 8 June 1955 is an English computer scientist who is credited The European Organization for Nuclear Research (Organisation Européenne pour la Recherche Nucléaire known as CERN As a result of the implementation of this project, in 1990 Berners-Lee wrote two programs:

• a browser called WorldWideWeb;
• the world's first web server, which ran on NeXTSTEP. A web browser is a software application which enables a user to display and interact with text images videos music games and other information typically located on a WorldWideWeb was the world's first Web browser and WYSIWYG HTML editor. Nextstep was the original object-oriented, multitasking Operating system that NeXT Computer developed to run on its range of proprietary computers

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 lots of different social groups of people, first in scientific organizations, then in universities and finally in industry.

In 1994 Tim Berners-Lee decided to constitute the World Wide Web Consortium to regulate the further development of the many technologies involved (HTTP, HTML, etc. ) through a standardization process.

The following years are recent history which has seen an exponential growth of the number of web sites and servers.

Market structure

Given below is a list of top Web server software vendors published in a Netcraft survey in April 2008. Netcraft is an Internet services company based in Bath, England.

There are hundreds of different web server programs available, many of which are specialized for very specific purposes, so the fact that a web server is not very popular does not necessarily mean that it has a lot of bugs or poor performance.

See Category:Web server software for a longer list of HTTP server programs.

See also

• Comparison of web servers
• Tiny web servers
• SSI, CGI, SCGI, FastCGI, PHP, Java Servlet, JavaServer Pages, ASP, ASP .NET, Server API
• Virtual hosting
• Web hosting service
• Web service
• Application server
• HTTP compression

External links

• RFC 2616, the Request for Comments document that defines the HTTP 1. This article is a comparison of Web servers. Please keep these in alphabetical order and when adding (or removing rows please check all tables in the article Lightweight web servers are Web servers which have been designed to run with very small resource overhead because of hardware environment or simply for the challenge of it Server Side Includes (SSI is a simple Server-side scripting language used almost exclusively for the web. The Common Gateway Interface ( CGI) is a standard protocol for interfacing external Application software with an information server The Simple Common Gateway Interface ( SCGI) is a protocol for applications to interface with HTTP servers an alternative to the CGI protocol PHP is a computer Scripting language. Originally designed for producing Dynamic web pages it has evolved to include a Command line interface capability The Java Servlet API allows a Software developer to add dynamic content to a Web server using the Java platform. JavaServer Pages ( JSP) is a Java technology that allows Software developers to dynamically generate HTML, XML or other types of documents Active Server Pages ( ASP) is Microsoft 's first server-side script engine for dynamically-generated web pages ASPNET is a Web application framework developed and marketed by Microsoft, that Programmers can use to build dynamic Web sites Web applications In Computer science, the Server Application Programming Interface (SAPI is the generic term used to designate direct module interfaces to Web server applications "vhost" redirects here for vhosts in relation to Internet Relay Chat see Vhost (IRC Virtual hosting is a method that servers A Web service (also Web Service) is defined by the W3C as "a software system designed to support interoperable machine-to-machine interaction In n-tier architecture an application server is a Server that hosts an API to expose Business Logic and Business Processes for use by other HTTP compression is a capability built into both Web servers and Web browsers to make better use of available bandwidth In Computer network Engineering, a Request for Comments (RFC is a Memorandum published by the Internet Engineering Task Force (IETF describing Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. 1 protocol.