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<title>Overview of new features in Apache HTTP Server 2.4 - Apache HTTP Server</title>
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<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.5</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.5</a></div><div id="page-content"><div id="preamble"><h1>Overview of new features in Apache HTTP Server 2.4</h1>
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<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
document.</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#core">Core Enhancements</a></li>
</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="section">
<h2><a name="core" id="core">Core Enhancements</a></h2>
<dl>
<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>Event MPM</dt>
<dd>The Event MPM is no longer experimental but is now fully supported.</dd>
<dt>Asynchronous support</dt>
platforms.</dd>
<dt>Per-module and per-directory LogLevel configuration</dt>
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>Per-request configuration sections</dt>
sections can be used to set the configuration based on per-request
criteria.</dd>
<dt>General-purpose expression parser</dt>
<dd>A new expression parser allows to specify
in directives like
and others.
</dd>
<dt>KeepAliveTimeout in milliseconds</dt>
<dd>It is now possible to specify <code class="directive"><a href="/mod/core.html#keepalivetimeout">KeepAliveTimeout</a></code> in milliseconds.
</dd>
<dt>NameVirtualHost directive</dt>
<dd>No longer needed and is now deprecated.</dd>
<dt>Override Configuration</dt>
<dd>The new <code class="directive"><a href="/mod/core.html#allowoverridelist">AllowOverrideList</a></code>
directive allows more fine grained control which directives are
allowed in <code>.htaccess</code> files. </dd>
<dt>Config file variables</dt>
variables in the configuration, allowing a clearer representation
if the same value is used at many places in the configuration.
</dd>
<dt>Reduced memory usage</dt>
<dd>Despite many new features, 2.4.x tends to use less memory than
2.2.x.</dd>
</dl>
<div class="section">
<h2><a name="newmods" id="newmods">New Modules</a></h2>
<dl>
<dd>FastCGI Protocol backend for <code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code></dd>
<dd>SCGI Protocol backend for <code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code></dd>
<dd>Provides dynamically configured mass reverse proxies for
<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>
<code class="module"><a href="/mod/mod_lbmethod_heartbeat.html">mod_lbmethod_heartbeat</a></code></dt>
<dd>Allow <code class="module"><a href="/mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> to base loadbalancing decisions
on the number of active connections on the backend servers.</dd>
<dd>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.</dd>
<dd>An advanced replacement of <code class="module"><a href="/mod/mod_substitute.html">mod_substitute</a></code>, allows
to edit the response body with the full power of sed.</dd>
<dd>Allows to do form-based authentication.</dd>
<dd>Allows to keep session state for clients, using cookie or
database storage.</dd>
<dd>New module to restrict certain HTTP methods without interfering with
authentication or authorization.</dd>
for configuration and small business logic functions. (Experimental)</dd>
<dd>Allows to add customizable debug logging at different phases of the
request processing.</dd>
<dd>Provides for buffering the input and output filter stacks</dd>
<dd>Convert response body into an RFC2397 data URL</dd>
<dd>Provides Bandwidth Rate Limiting for Clients</dd>
<dd>Provides Filters to handle and make available HTTP request bodies</dd>
<dd>Provides Reflection of a request body as a response via the output filter stack.</dd>
<dd>Provides a Slot-based shared memory provider (ala the scoreboard).</dd>
<dd>Formerly a third-party module, this supports internationalisation
in libxml2-based (markup-aware) filter modules.</dd>
</dl>
<div class="section">
<h2><a name="module" id="module">Module Enhancements</a></h2>
<dl>
<dd><code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code> 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><code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code> 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><code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code> can now be configured to share SSL Session
data between servers through memcached</dd>
<dd>EC keys are now supported in addition to RSA and DSA.</dd>
<dd>The <code class="directive"><a href="/mod/mod_proxy.html#proxypass">ProxyPass</a></code> directive
is now most optimally configured within a
block, and offers a significant performance advantage over the traditional
two-parameter syntax when present in large numbers.</dd>
<dd>The source address used for proxy requests is now configurable.</dd>
<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>
<dd>BalancerMembers can be set to 'Drain' so that they only respond to existing sticky
sessions, allowing them to be taken gracefully offline.</dd>
<dd>Balancer settings can be persistent after restarts.</dd>
<dd>The <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> CACHE filter can be optionally inserted
at a given point in the filter chain to provide fine control over caching.
</dd>
<dd><code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> can now cache HEAD requests.</dd>
<dd>Where possible, <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> 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><code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> is now capable of serving stale cached
data when a backend is unavailable (error 5xx).</dd>
<dd><code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> can now insert HIT/MISS/REVALIDATE into
an X-Cache header.</dd>
<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><code class="module"><a href="/mod/mod_cgi.html">mod_cgi</a></code>, <code class="module"><a href="/mod/mod_include.html">mod_include</a></code>,
<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><code class="module"><a href="/mod/mod_authz_core.html">mod_authz_core</a></code> Authorization Logic Containers</dt>
<dd>Advanced authorization logic may now be specified using the
and the related container directives, such as
<code class="directive"><a href="/mod/mod_authz_core.html#requireall"><RequireAll></a></code>.</dd>
<dd><code class="module"><a href="/mod/mod_rewrite.html">mod_rewrite</a></code> adds the <code>[QSD]</code>
(Query String Discard) and <code>[END]</code> flags for
simplify common rewriting scenarios.</dd>
<dd>Adds the possibility to use complex boolean expressions in <code class="directive"><a href="/mod/mod_rewrite.html#rewritecond">RewriteCond</a></code>.</dd>
<dd>Allows to use SQL queries as <code class="directive"><a href="/mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> functions.</dd>
<dt><code class="module"><a href="/mod/mod_ldap.html">mod_ldap</a></code>, <code class="module"><a href="/mod/mod_authnz_ldap.html">mod_authnz_ldap</a></code></dt>
<dd><code class="module"><a href="/mod/mod_authnz_ldap.html">mod_authnz_ldap</a></code> adds support for nested groups.</dd>
<code class="directive"><a href="/mod/mod_ldap.html#ldapconnectionpoolttl">LDAPConnectionPoolTTL</a></code>,
other improvements in the handling of timeouts.
This is especially useful for setups where a
stateful firewall drops idle connections to the LDAP server.</dd>
<code class="directive"><a href="/mod/mod_ldap.html#ldaplibrarydebug">LDAPLibraryDebug</a></code> to log
debug information provided by the used LDAP toolkit.</dd>
<dd><code class="module"><a href="/mod/mod_info.html">mod_info</a></code> can now dump the pre-parsed configuration
to stdout during server startup.</dd>
</dl>
<div class="section">
<h2><a name="programs" id="programs">Program Enhancements</a></h2>
<dl>
<dt>fcgistarter</dt>
<dd>New 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>
<dt>rotatelogs</dt>
<dd>May now create a link to the current log file.</dd>
<dd>May now invoke a custom post-rotate script.</dd>
</dl>
<div class="section">
<h2><a name="documentation" id="documentation">Documentation</a></h2>
<dl>
<dt>mod_rewrite</dt>
<dd>The <code class="module"><a href="/mod/mod_rewrite.html">mod_rewrite</a></code> documentation has been
rearranged and almost completely rewritten, with a focus on
examples and common usage, as well as on showing you when other
solutions are more appropriate. The <a href="rewrite/">Rewrite
Guide</a> is now a top-level section with much more detail and
better organization.</dd>
<dt>mod_ssl</dt>
<dd>The <code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code> documentation has been greatly
enhanced, with more examples at the getting started level, in
addition to the previous focus on technical details.</dd>
<dt>Caching Guide</dt>
features provided by <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code>, and the generic
interface, as well as to cover specialised caching provided by
mechanisms such as <code class="module"><a href="/mod/mod_file_cache.html">mod_file_cache</a></code>.</dd>
</dl>
<div class="section">
<h2><a name="developer" id="developer">Module Developer Changes</a></h2>
<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
<code class="program"><a href="/programs/httpd.html">httpd</a></code>. 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
expression parser previously implemented in
<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 <code class="directive"><a href="/mod/mod_authz_core.html#requireall"><RequireAll></a></code>.</dd>
<dt>Small-Object Caching Interface</dt>
interface for caching small data objects, based on the previous
implementation of the <code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code> 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 <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> 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
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