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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>

</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_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</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_fcgi</module></dt>

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

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

authentication or authorization.</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>

</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>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>, all

provided by the <module>mod_authz_core</module> module.</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>