Overview of new features in Apache 2.4

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This document describes some of the major changes between the 2.2 and 2.4 versions of the Apache HTTP Server. For new features since version 2.0, see the 2.2 new features document.

Core Enhancements
Module Enhancements
Program Enhancements
Module Developer Changes

Core Enhancements

KeepAliveTimeout in milliseconds: It is now possible to specify KeepAliveTimeout in milliseconds.
Simple MPM: Cleanroom MPM implementation with advanced thread pool management
Loadable MPMs: Multiple MPMs can now be built as loadable modules at compile time. The MPM of choice can be configured at run time.

Module Enhancements

mod_ssl: mod_ssl can now be configured to use an OCSP server to check the validation status of a client certificate. The default responder is configurable, along with the decision on whether to prefer the responder designated in the client certificate itself.; mod_ssl now also supports OCSP stapling, where the server pro-actively obtains an OCSP verification of its certificate and transmits that to the client during the handshake.; mod_ssl can now be configured to share SSL Session data between servers through memcached
mod_lua: Embeds the Lua language into httpd, for configuration and small business logic functions.
mod_proxy_fcgi: FastCGI Protocol backend for mod_proxy

Program Enhancements

fcgistarter: FastCGI deamon starter utility

Module Developer Changes

Check Configuration Hook Added: A new hook, check_config, has been added which runs between the pre_config and open_logs hooks. It also runs before the test_config hook when the -t option is passed to httpd. The check_config hook allows modules to review interdependent configuration directive values and adjust them while messages can still be logged to the console. The user can thus be alerted to misconfiguration problems before the core open_logs hook function redirects console output to the error log.
Expression Parser Added: We now have a general-purpose expression parser, whose API is exposed in ap_expr.h. This is adapted from the expression parser previously implemented in mod_include.
Authorization Logic Containers: Advanced authorization logic may now be specified using the Require directive and the related container directives, such as <RequireAll>, all provided by the mod_authz_core module.
Small-Object Caching Interface: The ap_socache.h header exposes a provider-based interface for caching small data objects, based on the previous implementation of the mod_ssl session cache. Providers using a shared-memory cyclic buffer, disk-based dbm files, and a memcache distributed cache are currently supported.