Apache现在的稳定系列是2.2(2.2.22) 遗留稳定版2.0/(2.0.64).2.3系列已经发布到了2.3.16-Beta.昨天官网的开发目录下已经出现了2.4.0的下载。按照惯例，相信很快2.4正式版就会发布（一般就是现有的包，不会有改动了）。尽管Nginx势头很猛，但相信使用Apache的仍然占大多数。 2.4.0分成两个包，把apr单独做成一个dep包。有兴趣的同学可以先尝试一下。按照惯例现有的包应该就是正式版本。

下载 http://httpd.apache.org/dev/dist/httpd-2.4.0.tar.bz2 http://httpd.apache.org/dev/dist/httpd-2.4.0-deps.tar.bz2

2.4对比2.2的完全改进：

It is now possible to specify KeepAliveTimeout in milliseconds.

Loadable MPMs

Multiple MPMs can now be built as loadable modules at compile time. The MPM of choice can be configured at run time.

Per-module and per-directory LogLevel configuration

The LogLevel can now be configured per module and per directory. New levels trace1 to trace8 have been added above the debug log level.

Event MPM

The Event MPM is no longer experimental but is now fully supported.

Asynchronous support

Better support for asynchronous read/write for supporting MPMs and platforms.

Per-request configuration sections

< If> sections can be used to set the configuration based on per-request criteria

General-purpose expression parser

A new expression parser allows to specify complex conditions using a common syntax in directives like SetEnvIfExpr, RewriteCond, Header, <If>, and others.

Reduced memory usage

Despite many new features, 2.4.x tends to use less memory than 2.2.x.

NameVirtualHost directive

No longer needed and is now deprecated.

KeepAliveTimeout in milliseconds

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mod_allowmethods

New module to restrict certain HTTP methods without interfering with authentication or authorization.

mod_buffer

Provides for buffering the input and output filter stacks

mod_data

Convert response body into an RFC2397 data URL

mod_lua

Embeds the Lua language into httpd, for configuration and small business logic functions.

mod_proxy_express

Provides dynamically configured mass reverse proxies for mod_proxy

mod_proxy_fcgi

FastCGI Protocol backend for mod_proxy

mod_proxy_scgi

SCGI Protocol backend for mod_proxy

mod_ratelimit

Provides Bandwidth Rate Limiting for Clients

mod_reflector

Provides Reflection of a request body as a response via the output filter stack.

mod_remoteip

Replaces the apparent client remote IP address and hostname for the request with the IP address list presented by a proxies or a load balancer via the request headers.

mod_reqtimeout

Set timeout and minimum data rate for receiving requests

mod_request

Provides Filters to handle and make available HTTP request bodies

mod_slotmem_shm

Provides a Slot-based shared memory provider (ala the scoreboard).

mod_log_debug

Allows to add customizable debug logging at different phases of the request processing.

mod_xml2enc

Formerly a third-party module, this supports internationalisation in libxml2-based (markup-aware) filter modules.

mod_proxy_html

Formerly a third-party module, this supports fixing of HTML links in a reverse proxy situation, where the backend generates URLs that are not valid for the proxy's clients.

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_proxy

The ProxyPass directive is now most optimally configured within a Location or LocationMatch block, and offers a significant performance advantage over the traditional two-parameter syntax when present in large numbers.

mod_proxy_balancer

More runtime configuration changes for BalancerMembers via balancer-manager

Additional BalancerMembers can be added at runtime via balancer-manager

Runtime configuration of a subset of Balancer parameters

BalancerMembers can be set to 'Drain' so that they only respond to existing sticky sessions, allowing them to be taken gracefully offline.

Balancer settings can be persistant after restarts.

mod_cache

mod_cache can now cache HEAD requests.

Where possible, mod_cache directives can now be set per directory, instead of per server.

The base URL of cached URLs can be customised, so that a cluster of caches can share the same endpoint URL prefix.

mod_cache is now capable of serving stale cached data when a backend is unavailable (error 5xx).

mod_cache can now insert HIT/MISS/REVALIDATE into an X-Cache header.

mod_include

Support for the 'onerror' attribute within an 'include' element, allowing an error document to be served on error instead of the default error string.

mod_cgi, mod_include, mod_isapi, ...

Translation of headers to environment variables is more strict than before to mitigate some possible cross-site-scripting attacks via header injection. Headers containing invalid characters (including underscores) are now silently dropped. Environment Variables in Apache has some pointers on how to work around broken legacy clients which require such headers. (This affects all modules which use these environment variables.)

mod_authz_core Authorization Logic Containers

Advanced authorization logic may now be specified using the Require directive and the related container directives, such as <RequireAll>.

mod_info

mod_info can now dump the pre-parsed configuration to stdout during server startup.

mod_rewrite

mod_rewrite adds the [QSD] (Query String Discard) and [END] flags for RewriteRule to simplify common rewriting scenarios.

mod_ldap, mod_authnz_ldap

mod_authnz_ldap adds support for nested groups.

mod_ldap adds LDAPConnectionPoolTTL, LDAPTimeout, and other improvements in the handling of timeouts. This is especially useful for setups where a stateful firewall drops idle connections to the LDAP server.

mod_ldap adds LDAPLibraryDebug to log debug information provided by the used LDAP toolkit.

fcgistarter

FastCGI deamon starter utility

htcacheclean

Current cached URLs can now be listed, with optional metadata included.

Allow explicit deletion of individual cached URLs from the cache.

File sizes can now be rounded up to the given block size, making the size limits map more closely to the real size on disk.

Cache size can now be limited by the number of inodes, instead of or in addition to being limited by the size of the files on disk.