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<title>Overview of new features in Apache HTTP Server 2.4</title>

<summary>

<p>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 <a href="new_features_2_2.html">2.2 new features</a>

document.</p>

</summary>

<section id="core">

<title>Core Enhancements</title>

<dl>

<dt>KeepAliveTimeout in milliseconds</dt>

<dd>It is now possible to specify <directive module="core"

>KeepAliveTimeout</directive> in milliseconds.

</dd>

<dt>Loadable MPMs</dt>

<dd>Multiple MPMs can now be built as loadable modules at compile time.

The MPM of choice can be configured at run time.</dd>

<dt>Per-module and per-directory LogLevel configuration</dt>

<dd>The <directive module="core">LogLevel</directive> can now be

configured per module and per directory. New levels <code>trace1</code>

to <code>trace8</code> have been added above the <code>debug</code> log

level.</dd>

<dt>Event MPM</dt>

<dd>The Event MPM is no longer experimental but is rather fully supported.</dd>

<dt>Asynchronous support</dt>

<dd>Better support for asynchronous read/write for supporting MPMs and

platforms.</dd>

<dt>Per-request configuration sections</dt>

<dd>&lt;<directive module="core">If</directive>&gt; sections can be used to

set the configuration based on per-request criteria</dd>

</dl>

</section>

<section id="newmods">

<title>New Modules</title>

<dl>

<dt><module>mod_allowmethods</module></dt>

<dd>New module to restrict certain HTTP methods without interfering with

authentication or authorization.</dd>

<dt><module>mod_buffer</module></dt>

<dd>Provides for buffering the input and output filter stacks</dd>

<dt><module>mod_lua</module></dt>

<dd>Embeds the <a href="http://www.lua.org/">Lua</a> language into httpd,

for configuration and small business logic functions.</dd>

<dt><module>mod_proxy_fcgi</module></dt>

<dd>FastCGI Protocol backend for <module>mod_proxy</module></dd>

<dt><module>mod_proxy_scgi</module></dt>

<dd>SCGI Protocol backend for <module>mod_proxy</module></dd>

<dt><module>mod_ratelimit</module></dt>

<dd>Provides Bandwidth Rate Limiting for Clients</dd>

<dt><module>mod_reflector</module></dt>

<dd>Provides Reflection of a request body as a response via the output filter stack.</dd>

<dt><module>mod_remoteip</module></dt>

<dd>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.</dd>

<dt><module>mod_reqtimeout</module></dt>

<dd>Set timeout and minimum data rate for receiving requests</dd>

<dt><module>mod_request</module></dt>

<dd>Provides Filters to handle and make available HTTP request bodies</dd>

<dt><module>mod_slotmem_shm</module></dt>

<dd>Provides a Slot-based shared memory provider (ala the scoreboard).</dd>

</dl>

</section>

<section id="module">

<title>Module Enhancements</title>

<dl>

<dt><module>mod_ssl</module></dt>

<dd><module>mod_ssl</module> 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.</dd>

<dd><module>mod_ssl</module> 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. </dd>

<dd><module>mod_ssl</module> can now be configured to share SSL Session

data between servers through memcached</dd>

<dt><module>mod_proxy</module></dt>

<dd>The <directive module="mod_proxy">ProxyPass</directive> directive

is now most optimally configured within a

<directive module="core">Location</directive> or

<directive module="core">LocationMatch</directive>

block, and offers a significant performance advantage over the traditional

two-parameter syntax when present in large numbers.</dd>

<dt><module>mod_proxy_balancer</module></dt>

<dd>More runtime configuration changes for BalancerMembers via balancer-manager</dd>

<dd>Additional BalancerMembers can be added at runtime via balancer-manager</dd>

<dd>Runtime configuration of a subset of Balancer parameters</dd>

<dt><module>mod_cache</module></dt>

<dd><module>mod_cache</module> can now cache HEAD requests.</dd>

<dd>Where possible, <module>mod_cache</module> directives can now be set

per directory, instead of per server.</dd>

<dd>The base URL of cached URLs can be customised, so that a cluster of

caches can share the same endpoint URL prefix.</dd>

<dd><module>mod_cache</module> is now capable of serving stale cached

data when a backend is unavailable (error 5xx).</dd>

<dd><module>mod_cache</module> can now insert HIT/MISS/REVALIDATE into

an X-Cache header.</dd>

<dt><module>mod_include</module></dt>

<dd>Support for the 'onerror' attribute within an 'include' element,

allowing an error document to be served on error instead of the default

error string.</dd>

<dt><module>mod_cgi</module>, <module>mod_include</module>,

<module>mod_isapi</module>, ...</dt>

<dd>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. <a href="env.html">Environment Variables

in Apache</a> has some pointers on how to work around broken legacy

clients which require such headers. (This affects all modules which

use these environment variables.)</dd>

<dt><module>mod_authz_core</module> Authorization Logic Containers</dt>

<dd>Advanced authorization logic may now be specified using the

<directive module="mod_authz_core">Require</directive> directive

and the related container directives, such as

<directive module="mod_authz_core"

type="section">RequireAll</directive>.</dd>

<dt><module>mod_info</module></dt>

<dd><module>mod_info</module> can now dump the pre-parsed configuration

to stdout during server startup.</dd>

</dl>

</section>

<section id="programs">

<title>Program Enhancements</title>

<dl>

<dt>fcgistarter</dt>

<dd>FastCGI deamon starter utility</dd>

<dt>htcacheclean</dt>

<dd>Current cached URLs can now be listed, with optional metadata

included.</dd>

<dd>Allow explicit deletion of individual cached URLs from the

cache.</dd>

<dd>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.</dd>

<dd>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.</dd>

</dl>

</section>

<section id="developer">

<title>Module Developer Changes</title>

<dl>

<dt>Check Configuration Hook Added</dt>

<dd>A new hook, <code>check_config</code>, has been added which runs

between the <code>pre_config</code> and <code>open_logs</code>

hooks. It also runs before the <code>test_config</code> hook

when the <code>-t</code> option is passed to

<program>httpd</program>. The <code>check_config</code> 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 <code>open_logs</code> hook function redirects

console output to the error log.</dd>

<dt>Expression Parser Added</dt>

<dd>We now have a general-purpose expression parser, whose API is

exposed in <var>ap_expr.h</var>. This is adapted from the

expression parser previously implemented in

<module>mod_include</module>.</dd>

<dt>Authorization Logic Containers</dt>

<dd>Authorization modules now register as a provider, via

ap_register_auth_provider(), to support advanced authorization logic,

such as <directive module="mod_authz_core" type="section"

>RequireAll</directive>.</dd>

<dt>Small-Object Caching Interface</dt>

<dd>The <var>ap_socache.h</var> header exposes a provider-based

interface for caching small data objects, based on the previous

implementation of the <module>mod_ssl</module> session cache.

Providers using a shared-memory cyclic buffer, disk-based dbm

files, and a memcache distributed cache are currently

supported.</dd>

<dt>Cache Status Hook Added</dt>

<dd>The <module>mod_cache</module> module now includes a new

<code>cache_status</code> hook, which is called when the caching

decision becomes known. A default implementation is provided

which adds an optional <code>X-Cache</code> and

<code>X-Cache-Detail</code> header to the response.</dd>

</dl>

<p>The developer documentation contains a

<a href="developer/new_api_2_4.html">detailed list of API changes</a>.</p>

</section>

</manualpage>