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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>Run-time Loadable MPMs</dt>

<dd>Multiple MPMs can now be <a href="mpm.html#dynamic">built

as loadable modules</a> at compile time.

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

<dt>Event MPM</dt>

<dd>The <a href="mod/event.html">Event MPM</a> is no longer experimental

but is now fully supported.</dd>

<dt>Asynchronous support</dt>

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

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

<dd><directive module="core" type="section">If</directive>,

<directive module="core" type="section">ElseIf</directive>,

and <directive module="core" type="section">Else</directive>

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

<a href="expr.html">complex conditions</a> using a common syntax

in directives like

<directive module="mod_setenvif">SetEnvIfExpr</directive>,

<directive module="mod_rewrite">RewriteCond</directive>,

<directive module="mod_headers">Header</directive>,

<directive module="core" type="section">If</directive>,

and others.

</dd>

<dt>KeepAliveTimeout in milliseconds</dt>

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

>KeepAliveTimeout</directive> in milliseconds.

</dd>

<dt>NameVirtualHost directive</dt>

<dd>No longer needed and is now deprecated.</dd>

<dt>Override Configuration</dt>

<dd>The new <directive module="core">AllowOverrideList</directive>

directive allows more fine grained control which directives are

allowed in <code>.htaccess</code> files. </dd>

<dt>Config file variables</dt>

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

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>

</section>

<section id="newmods">

<title>New Modules</title>

<dl>

<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_proxy_express</module></dt>

<dd>Provides dynamically configured mass reverse proxies for

<module>mod_proxy</module></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_heartmonitor</module>,

<module>mod_lbmethod_heartbeat</module></dt>

<dd>Allow <module>mod_proxy_balancer</module> to base loadbalancing decisions

on the number of active connections on the backend servers.</dd>

<dt><module>mod_proxy_html</module></dt>

<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>

<dt><module>mod_sed</module></dt>

<dd>An advanced replacement of <module>mod_substitute</module>, allows

to edit the response body with the full power of sed.</dd>

<dt><module>mod_auth_form</module></dt>

<dd>Enables form-based authentication.</dd>

<dt><module>mod_session</module></dt>

<dd>Enables the use of session state for clients, using cookie or

database storage.</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_lua</module></dt>

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

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

<dt><module>mod_log_debug</module></dt>

<dd>Allows the addition of customizable debug logging at different phases of the

request processing.</dd>

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

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

<dt><module>mod_data</module></dt>

<dd>Convert response body into an RFC2397 data URL</dd>

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

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

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

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

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

<dt><module>mod_xml2enc</module></dt>

<dd>Formerly a third-party module, this supports internationalisation

in libxml2-based (markup-aware) filter modules.</dd>

<dt><module>mod_macro</module> (available since 2.4.5)</dt>

<dd>Provide macros within configuration files.</dd>

<dt><module>mod_proxy_wstunnel</module> (available since 2.4.5)</dt>

<dd>Support web-socket tunnels.</dd>

<dt><module>mod_authnz_fcgi</module> (available since 2.4.10)</dt>

<dd>Enable FastCGI authorizer applications to authenticate and/or

authorize clients.</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>

<dd>EC keys are now supported in addition to RSA and DSA.</dd>

<dd>Support for TLS-SRP (available in 2.4.4 and later).</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>

<dd>The source address used for proxy requests is now configurable.</dd>

<dd>Support for Unix domain sockets to the backend (available in 2.4.7

and later).</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>

<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>

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

<dd>The <module>mod_cache</module> CACHE filter can be optionally inserted

at a given point in the filter chain to provide fine control over caching.

</dd>

<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_rewrite</module></dt>

<dd><module>mod_rewrite</module> adds the <code>[QSD]</code>

(Query String Discard) and <code>[END]</code> flags for

<directive module="mod_rewrite">RewriteRule</directive> to

simplify common rewriting scenarios.</dd>

<dd>Adds the possibility to use complex boolean expressions in <directive

module="mod_rewrite">RewriteCond</directive>.</dd>

<dd>Allows the use of SQL queries as <directive

module="mod_rewrite">RewriteMap</directive> functions.</dd>

<dt><module>mod_ldap</module>, <module>mod_authnz_ldap</module></dt>

<dd><module>mod_authnz_ldap</module> adds support for nested groups.</dd>

<dd><module>mod_ldap</module> adds

<directive module="mod_ldap">LDAPConnectionPoolTTL</directive>,

<directive module="mod_ldap">LDAPTimeout</directive>, 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.</dd>

<dd><module>mod_ldap</module> adds

<directive module="mod_ldap">LDAPLibraryDebug</directive> to log

debug information provided by the used LDAP toolkit.</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>

<dt><module>mod_auth_basic</module></dt>

<dd>New generic mechanism to fake basic authentication (available in

2.4.5 and later).</dd>

</dl>

</section>

<section id="programs">

<title>Program Enhancements</title>

<dl>

<dt><program>fcgistarter</program></dt>

<dd>New FastCGI deamon starter utility</dd>

<dt><program>htcacheclean</program></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><program>rotatelogs</program></dt>

<dd>May now create a link to the current log file.</dd>

<dd>May now invoke a custom post-rotate script.</dd>

<dt><program>htpasswd</program>, <program>htdbm</program></dt>

<dd>Support for the bcrypt algorithm (available in 2.4.4 and later).

</dd>

</dl>

</section>

<section id="documentation">

<title>Documentation</title>

<dl>

<dt>mod_rewrite</dt>

<dd>The <module>mod_rewrite</module> 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 <module>mod_ssl</module> 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>

<dd>The <a href="caching.html">Caching Guide</a> has been rewritten

to properly distinguish between the RFC2616 HTTP/1.1 caching

features provided by <module>mod_cache</module>, and the generic

key/value caching provided by the <a href="socache.html">socache</a>

interface, as well as to cover specialised caching provided by

mechanisms such as <module>mod_file_cache</module>.</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_ssl</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>