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<manualpage metafile="new_features_2_4.xml.meta">

<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 via <directive
      module="mod_so">LoadModule</directive> directive.</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>

      <dt><module>mod_http2</module> (available since 2.4.17)</dt>
      <dd>Support for the HTTP/2 transport layer.</dd>

      <dt><module>mod_proxy_http2</module> (available since 2.4.19)</dt>
      <dd>HTTP/2 Protocol backend for <module>mod_proxy</module></dd>

      <dt><module>mod_proxy_hcheck</module> (available since 2.4.21)</dt>
      <dd>Support independent dynamic health checks for remote proxiy backend servers.</dd>

      <dt><module>mod_brotli</module> (available since 2.4.26)</dt>
      <dd>Support the Brotli compression algorithm.</dd>

      <dt><module>mod_md</module> (available since 2.4.30)</dt>
      <dd>Support the ACME protocol to automate certificate provisionning.</dd>

      <dt><module>mod_proxy_uwsgi</module> (available since 2.4.30)</dt>
      <dd>UWSGI gateway module for <module>mod_proxy</module>.</dd>

      <dt><module>mod_socache_redis</module> (available since 2.4.39)</dt>
      <dd>Support <a href="http://redis.io/">Redis</a> based shared object cache provider.</dd>

      <dt><module>mod_systemd</module> (available since 2.4.42)</dt>
      <dd>systemd integration. It allows httpd to be used in a service with the systemd
      <code>Type=notify</code>.</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. Header names containing invalid characters (including underscores)
      are no longer converted to environment variables. <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 daemon 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>