The Apache Project is a collaborative software development effort aimed at creating a robust, commercial-grade, featureful, and freely-available source code implementation of an HTTP (Web) server.
Originally designed as a replacement for the NCSA HTTP Server, Apache has grown to be one of the most popular web servers on the Internet. It’s extensible through a dynamically loadable module system and can process a large number of interpreted languages without connecting out to separate software.
Apache supports a variety of features, many implemented as compiled modules which extend the core functionality
- Virtual hosting which allows one Apache installation to serve many different actual websites.
- 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).
- Configurable error messages.
- DBMS-based authentication databases.
- Content negotiation.
- Supported by several graphical user interfaces (GUIs) which permit easier configuration of the server. Many features implemented as compiled modules, ranging from server-side programming language support to authentication schemes.
- Common language interfaces support include mod_perl, mod_python, Tcl, and PHP.
- Popular authentication modules include mod_access, mod_auth, and mod_digest.
- SSL and TLS support (mod_ssl).
- Proxy module.
- 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.
- Caching features to improve the performance:
- Three-state RFC2616 HTTP caching – mod_cache and its provider modules mod_cache_disk provide intelligent, HTTP-aware caching. The content itself is stored in the cache, and mod_cache aims to honor all of the various HTTP headers and options that control the cacheability of content.
- Two-state key/value shared object caching – the shared object cache API (socache) and its provider modules provide a server wide key/value based shared object cache. These modules are designed to cache low level data such as SSL sessions and authentication credentials. Backends allow the data to be stored server wide in shared memory, or datacenter wide in a cache such as memcache or distcache.
- Specialized file caching – mod_file_cache offers the ability to pre-load files into memory on server startup, and can improve access times and save file handles on files that are accessed often, as there is no need to go to disk on each request.
- URL rewriting (also known as a rewrite engine, implemented under mod_rewrite).
- HTTP/2 support.
- 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 – Web Distributed Authoring and Versioning is an extension of the Hypertext Transfer Protocol (HTTP) that allows clients to perform remote Web content authoring operations.
- Popular compression methods on Apache include the external extension module, mod_gzip, implemented to help with reduction of the size of web pages.
- Custom log files (mod_log_config).
- Filtering support (mod_include and mod_ext_filter).
- Handling of static files, index files, auto-indexing and content negotiation.
- XML support.
- Embedded Perl, PHP and Lua scripting.
- Real-time status views.
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