Apache HTTP Server Version 2.4
Apache HTTP Server Version 2.4
This document describes some of the major changes between the 2.0 and 2.2 versions of the Apache HTTP Server. For new features since version 1.3, see the 2.0 new features document.
mod_cache, mod_cache_disk, and mod_mem_cache(already removed from 2.3/2.4) have undergone a lot of changes, and are now considered production-quality. htcacheclean has been introduced to clean up mod_cache_disk setups.prefork, worker and event MPMs now allow httpd to be shutdown gracefully via the graceful-stop signal. The GracefulShutdownTimeout directive has been added to specify an optional timeout, after which httpd will terminate regardless of the status of any requests being served.mod_proxy_balancer module provides load balancing services for mod_proxy. The new mod_proxy_ajp module adds support for the Apache JServ Protocol version 1.3 used by Apache Tomcat.httpd can be configured to use a system installation of PCRE by passing the --with-pcre flag to configure.mod_filter introduces dynamic configuration to the output filter chain. It enables filters to be conditionally inserted, based on any Request or Response header or environment variable, and dispenses with the more problematic dependencies and ordering problems in the 2.0 architecture.httpd is now built with support for files larger than 2GB on modern 32-bit Unix systems. Support for handling >2GB request bodies has also been added.event MPM uses a separate thread to handle Keep Alive requests and accepting connections. Keep Alive requests have traditionally required httpd to dedicate a worker to handle it. This dedicated worker could not be used again until the Keep Alive timeout was reached.mod_dbd, together with the apr_dbd framework, brings direct SQL support to modules that need it. Supports connection pooling in threaded MPMs.
mod_auth is now split into mod_auth_basic and mod_authn_file; mod_auth_dbm is now called mod_authn_dbm; mod_access has been renamed mod_authz_host. There is also a new mod_authn_alias(already removed from 2.3/2.4) module for simplifying certain authentication configurations.mod_authnz_ldapmod_auth_ldap module to the 2.2 Authn/Authz framework. New features include using LDAP attribute values and complicated search filters in the Require directive.mod_authz_ownermod_versionmod_info?config argument which will show the configuration directives as parsed by Apache, including their file name and line number. The module also shows the order of all request hooks and additional build information, similar to httpd -V.mod_sslmod_imagemapmod_imap has been renamed to mod_imagemap to avoid user confusion.
httpd-M has been added that lists all modules that are loaded based on the current configuration. Unlike the -l option, this list includes DSOs loaded via mod_so.httxt2dbmRewriteMap with the dbm map type.
APR and APR-Util. For details, see the APR Website.mod_auth_* -> Modules that implement an HTTP authentication mechanismmod_authn_* -> Modules that provide a backend authentication providermod_authz_* -> Modules that implement authorization (or access)mod_authnz_* -> Module that implements both authentication & authorizationap_log_cerror has been added to log errors that occur with the client's connection. When logged, the message includes the client IP address.test_config has been added to aid modules that want to execute special code only when the user passes -t to httpd.ThreadStackSize has been added to set the stack size on all threaded MPMs. This is required for some third-party modules on platforms with small default thread stack size.mod_filter, using the ap_register_output_filter_protocol or ap_filter_protocol calls.pcreposix.h header is no longer available; it is replaced by the new ap_regex.h header. The POSIX.2 regex.h implementation exposed by the old header is now available under the ap_ namespace from ap_regex.h. Calls to regcomp, regexec and so on can be replaced by calls to ap_regcomp, ap_regexec.With Apache 1.x and 2.0, modules requiring an SQL backend had to take responsibility for managing it themselves. Apart from reinventing the wheel, this can be very inefficient, for example when several modules each maintain their own connections.
Apache 2.1 and later provides the ap_dbd API for managing database connections (including optimised strategies for threaded and unthreaded MPMs), while APR 1.2 and later provides the apr_dbd API for interacting with the database.
New modules SHOULD now use these APIs for all SQL database operations. Existing applications SHOULD be upgraded to use it where feasible, either transparently or as a recommended option to their users.