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Apache HTTP Server

Original author(s)	Robert McCool
Developer(s)	Apache Software Foundation
Initial release	1995; 29 years ago (1995)
Repository	github.com/apache/httpd
Written in	C, XML
Operating system	Unix-like, Windows
Type	Web server
License	Apache License 2.0
Website	httpd.apache.org

The Apache HTTP Server, colloquially called Apache (/əˈpætʃiː/ ə-PA-chee), is the world's most used web server software. Originally based on the NCSA HTTPd server, development of Apache began in early 1995 after work on the NCSA code stalled. Apache played a key role in the initial growth of the World Wide Web, quickly overtaking NCSA HTTPd as the dominant HTTP server, and has remained most popular since April 1996. In 2009, it became the first web server software to serve more than 100 million websites.

Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation. Most commonly used on a Unix-like system (usually Linux), the software is available for a variety of operating systems besides Unix, including Microsoft Windows. Version 2.0 improved support for non-Unix, e.g. Windows and OS/2 (and eComStation). Old versions of Apache were ported to run on e.g. OpenVMS, and NetWare. Released under the Apache License, Apache is free and open-source software.

As of July 2016, Apache was estimated to serve 46.41% of all active websites and 43.18% of the top million websites.

Name

According to the FAQ in the Apache project website, the name Apache was chosen out of respect to the Native American tribe Apache and their superior skills in warfare and strategy. The name was widely believed to be a pun on 'A Patchy Server' (since it was a set of software patches). Official documentation used to give this explanation of the name, but in a 2000 interview, Brian Behlendorf, one of the creators of Apache, set the record straight:

The name literally came out of the blue. I wish I could say that it was something fantastic, but it was out of the blue. I put it on a page and then a few months later when this project started, I pointed people to this page and said: "Hey, what do you think of that idea?" ... Someone said they liked the name and that it was a really good pun. And I was like, "A pun? What do you mean?" He said, "Well, we're building a server out of a bunch of software patches, right? So it's a patchy Web server." I went, "Oh, all right." ... When I thought of the name, no. It just sort of connotated: "Take no prisoners. Be kind of aggressive and kick some ass."

When Apache is running, its process name is sometimes httpd, which is short for "HTTP daemon."

Feature overview

Apache supports a variety of features, many implemented as compiled modules which extend the core functionality. These can range from server-side programming language support to authentication schemes. Some common language interfaces support Perl, Python, Tcl, and PHP. Popular authentication modules include mod_access, mod_auth, mod_digest, and mod_auth_digest, the successor to mod_digest. A sample of other features include Secure Sockets Layer and Transport Layer Security support (mod_ssl), a proxy module (mod_proxy), a URL rewriting module (mod_rewrite), custom log files (mod_log_config), and filtering support (mod_include and mod_ext_filter).

Popular compression methods on Apache include the external extension module, mod_gzip, implemented to help with reduction of the size (weight) of Web pages served over HTTP. ModSecurity is an open source intrusion detection and prevention engine for Web applications. Apache logs can be analyzed through a Web browser using free scripts, such as AWStats/W3Perl or Visitors.

Virtual hosting allows one Apache installation to serve many different Web sites. For example, one machine with one Apache installation could simultaneously serve www.example.com, www.example.org, test47.test-server.example.edu, etc.

Apache features configurable error messages, DBMS-based authentication databases, and content negotiation. It is also supported by several graphical user interfaces (GUIs).

It supports password authentication and digital certificate authentication. Because the source code is freely available, anyone can adapt the server for specific needs, and there is a large public library of Apache add-ons.

HTTP server and proxy features

This article is in list format but may read better as prose. You can help by converting this article, if appropriate. Editing help is available. (August 2016)

• Loadable Dynamic Modules
• Multiple Request Processing modes (MPMs) including Event-based/Async, Threaded and Prefork.
• Highly scalable (easily handles more than 10,000 simultaneous connections)
• Handling of static files, index files, auto-indexing and content negotiation
• .htaccess support
• Reverse proxy with caching
  • Load balancing with in-band health checks
  • Multiple load balancing mechanisms
  • Fault tolerance and Failover with automatic recovery
  • WebSocket, FastCGI, SCGI, AJP and uWSGI support with caching
  • Dynamic configuration
• TLS/SSL with SNI and OCSP stapling support, via OpenSSL.
• Name- and IP address-based virtual servers
• IPv6-compatible
• HTTP/2 protocol support
• Fine-grained authentication and authorization access control
• gzip compression and decompression
• URL rewriting
• Headers and content rewriting
• Custom logging with rotation
• Concurrent connection limiting
• Request processing rate limiting
• Bandwidth throttling
• Server Side Includes
• IP address-based geolocation
• User and Session tracking
• WebDAV
• Embedded Perl, PHP and Lua scripting
• CGI support
• public_html per-user web-pages
• Generic expression parser
• Real-time status views
• XML support

Performance

Instead of implementing a single architecture, Apache provides a variety of MultiProcessing Modules (MPMs), which allow Apache to run in a process-based, hybrid (process and thread) or event-hybrid mode, to better match the demands of each particular infrastructure. This implies that the choice of correct MPM and the correct configuration is important. Where compromises in performance need to be made, the design of Apache is to reduce latency and increase throughput, relative to simply handling more requests, thus ensuring consistent and reliable processing of requests within reasonable time-frames.

For delivery of static pages, Apache 2.2 series was considered significantly slower than nginx and varnish. To address this issue, the Apache developers created the Event MPM, which mixes the use of several processes and several threads per process in an asynchronous event-based loop. This architecture, and the way it was implemented in the Apache 2.4 series, provides for performance equivalent or slightly better than event-based web servers, as is cited by Jim Jagielski and other independent sources. However, some independent, but significantly outdated, benchmarks show that it still is half as fast as nginx, e.g.

Licensing

The Apache HTTP Server codebase was relicensed to the Apache 2.0 License (from the previous 1.1 license) in January 2004, and Apache HTTP Server 1.3.31 and 2.0.49 were the first releases using the new license.

The OpenBSD project did not like the change and continued the use of pre-2.0 Apache versions, effectively forking Apache 1.3.x for its purposes. They initially replaced it with Nginx, and soon after made their own replacement, OpenBSD Httpd, based on the relayd project.

Versions

Version 1.1: The Apache License 1.1 was approved by the ASF in 2000: The primary change from the 1.0 license is in the 'advertising clause' (section 3 of the 1.0 license); derived products are no longer required to include attribution in their advertising materials, but only in their documentation.

Version 2.0: The ASF adopted the Apache License 2.0 in January 2004. The stated goals of the license included making the license easier for non-ASF projects to use, improving compatibility with GPL-based software, allowing the license to be included by reference instead of listed in every file, clarifying the license on contributions, and requiring a patent license on contributions that necessarily infringe a contributor's own patents.

Development

The Apache HTTP Server Project is a collaborative software development effort aimed at creating a robust, commercial-grade, feature-rich and freely available source code implementation of an HTTP (Web) server. The project is jointly managed by a group of volunteers located around the world, using the Internet and the Web to communicate, plan, and develop the server and its related documentation. This project is part of the Apache Software Foundation. In addition, hundreds of users have contributed ideas, code, and documentation to the project.

Apache 2.4 dropped support for BeOS, TPF and even older platforms.

See also

• .htaccess
• .htpasswd
• ApacheBench
• Comparison of web server software
• IBM HTTP Server
• LAMP (software bundle)
• List of Apache modules
• POSSE project
• suEXEC

References

1. "About the Apache HTTP Server Project". Apache Software Foundation. Archived from the original on 7 June 2008. Retrieved 2008-06-25. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
2. https://projects-old.apache.org/indexes/language.html
3. "Languages". Apache HTTP Server. Black Duck Software. Ohloh. Retrieved 2 April 2014.
4. "Compiling and Installing". httpd.apache.org. The Apache Software Foundation. Retrieved 9 May 2016.
5. Netcraft Market Share for Top Servers Across All Domains August 1995 - today (monthly updated)
6. "February 2009 Web Server Survey". Netcraft. Archived from the original on 26 February 2009. Retrieved 2009-03-29. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
7. "OS/Linux Distributions using Apache". 1 August 2009.
8. "Overview of new features in Apache 2.0". Apache 2.0 is faster and more stable on non-Unix platforms such as OS/2, and Windows.
9. "HP OpenVMS systems - Secure Web Server (based on Apache)". h41379.www4.hpe.com.
10. "July 2016 Web Server Survey". Netcraft. Netcraft. Archived from the original on 10 August 2016. Retrieved 10 August 2016.
11. "Why the name 'Apache'?". HTTPd Frequently Asked Questions.
12. "Information on the Apache HTTP Server Project". 1997-04-15. Archived from the original on April 15, 1997. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
13. "Apache Server Frequently Asked Questions". Archived from the original on 1997-01-06. Retrieved 15 January 2017.
14. "Apache Power". Linux Magazine.
15. "What is Apache Web Server? Webopedia". webopedia.com.
16. "Apache HTTP Server Tutorial: .htaccess files".
17. "mod_proxy".
18. "mod_proxy_balancer".
19. "Balancer Manager".
20. "Authentication and Authorization".
21. "mod_rewrite".
22. "mod_headers".
23. "mod_sed".
24. "mod_substitute".
25. "Apache httpd Tutorial: Introduction to Server Side Includes".
26. "mod_usertrack".
27. "Apache Tutorial: Dynamic Content with CGI".
28. "Per-user web directorie".
29. "Expressions in Apache HTTP Server".
30. "mod_status".
31. "mod_xml2enc".
32. "Serving static files: a comparison between Apache, Nginx, Varnish and G-WAN". Spoot!.
33. "worker - Apache HTTP Server Version 2.2". apache.org.
34. Apache httpd 2.4
35. "Picking a Proxy Server".
36. "Throughput evaluation of Apache 2.4.1".
37. "Performance of Apache 2.4 with the event MPM compared to Nginx". eschrade.com.
38. "Apache License, Version 2.0". The Apache Software Foundation. January 2004. Retrieved 2013-05-21.
39. Burton, Richard Antony. "FYI: Apache HTTP Server 2.0.49 Released". Newsgroup: alt.apache.configuration. {{cite newsgroup}}: |access-date= requires |url= (help)
40. de Raadt, Theo (18 February 2004). "The new apache license". openbsd-misc (Mailing list). Retrieved 2013-05-21. {{cite mailing list}}: Unknown parameter |mailinglist= ignored (|mailing-list= suggested) (help)
41. "Copyright Policy". OpenBSD. Retrieved 2013-05-12.
42. "apache-httpd-openbsd-1.3.20140502p2 – OpenBSD improved and secured version of Apache 1.3". OpenBSD ports. Retrieved 2014-12-28.
43. "OpenBSD Upgrade Guide: 5.1 to 5.2". openbsd.org.
44. jj, ed. (2014-03-14). "Heads Up: Apache Removed from Base". OpenBSD Journal.
45. "OpenBSD Upgrade Guide: 5.5 to 5.6". openbsd.org.
46. "Announcement: Apache 1.3.0 Released !". 1998-06-06. Retrieved 2015-01-06.
47. "Apache HTTP Server 1.3.42 released (final release of 1.3.x)". apache.org.
48. "Official Release: Apache 2.0.35 is now GA". 2002-04-06. Retrieved 2015-01-06.
49. "[Announcement] Apache HTTP Server 2.0.65 Released". apache.org.
50. "Apache HTTP Server 2.2.0 Released". 2005-12-01. Retrieved 2015-01-06.
51. "[Announce] Apache HTTP Server 2.2.32 Released". apache.org.
52. "[ANNOUNCEMENT] Apache HTTP Server 2.4.1 Released". 2012-02-21. Retrieved 2015-07-17.
53. "Apache HTTP Server 2.4.25 Released". apache.org.
54. Documentation Group. "About the Apache HTTP Server Project - The Apache HTTP Server Project". apache.org.
55. The Apache HTTP Server Open Source Project on Ohloh. (n.d.). Ohloh, the open source network. Retrieved November 12, 2012
56. "Chapter 4. The Apache HTTP Server". fedoraproject.org.
57. "Upgrading to 2.4 from 2.2". Platform support has been removed for BeOS, TPF, and even older platforms such as A/UX, Next, and Tandem. These were believed to be broken anyway.

External links

• Official website

• 1995 software
• Apache Software Foundation
• Apache Software Foundation projects
• Cross-platform free software
• Free software programmed in C
• Free web server software
• Reverse proxy
• Software using the Apache license
• Unix network-related software
• Web server software for Linux