Overview of new features in Apache HTTP Server 2.4 - Apache HTTP Server Version 2.4








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Apache HTTP Server Version 2.4



Apache > HTTP Server > Documentation > Version 2.4Overview of new features in Apache HTTP Server 2.4

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  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 2.2 new features
     document.

 Core Enhancements
 New Modules
 Module Enhancements
 Program Enhancements
 Documentation
 Module Developer Changes
See alsoComments


Core Enhancements
    
    
      Run-time Loadable MPMs
      Multiple MPMs can now be built
      as loadable modules at compile time.
      The MPM of choice can be configured at run time via LoadModule directive.

      Event MPM
      The Event MPM is no longer experimental
      but is now fully supported.

      Asynchronous support
      Better support for asynchronous read/write for supporting MPMs and
      platforms.

      Per-module and per-directory LogLevel configuration
      The LogLevel can now be
      configured per module and per directory.  New levels trace1
      to trace8 have been added above the debug log
      level.

      Per-request configuration sections
      <If>,
          <ElseIf>,
          and <Else>
          sections can be used to set the configuration based on per-request
          criteria.

      General-purpose expression parser
      A new expression parser allows to specify
          complex conditions using a common syntax
          in directives like
          SetEnvIfExpr,
          RewriteCond,
          Header,
          <If>,
          and others.
      

      KeepAliveTimeout in milliseconds
      It is now possible to specify KeepAliveTimeout in milliseconds.
      

      NameVirtualHost directive
      No longer needed and is now deprecated.

      Override Configuration
      The new AllowOverrideList
          directive allows more fine grained control which directives are
          allowed in .htaccess files. 

      Config file variables
      It is now possible to Define
          variables in the configuration, allowing a clearer representation
          if the same value is used at many places in the configuration.
      

      Reduced memory usage
      Despite many new features, 2.4.x tends to use less memory than
      2.2.x.

    
  

New Modules
    
    
      mod_proxy_fcgi
      FastCGI Protocol backend for mod_proxy

      mod_proxy_scgi
      SCGI Protocol backend for mod_proxy

      mod_proxy_express
      Provides dynamically configured mass reverse proxies for
      mod_proxy

      mod_remoteip
      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.

      mod_heartmonitor,
          mod_lbmethod_heartbeat
      Allow mod_proxy_balancer to base loadbalancing decisions
      on the number of active connections on the backend servers.

      mod_proxy_html
      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.

      mod_sed
      An advanced replacement of mod_substitute, allows
      to edit the response body with the full power of sed.

      mod_auth_form
      Enables form-based authentication.

      mod_session
      Enables the use of session state for clients, using cookie or
      database storage.

      mod_allowmethods
      New module to restrict certain HTTP methods without interfering with
      authentication or authorization.

      mod_lua
      Embeds the Lua language into httpd,
      for configuration and small business logic functions. (Experimental)

      mod_log_debug
      Allows the addition of customizable debug logging at different phases of the
      request processing.

      mod_buffer
      Provides for buffering the input and output filter stacks

      mod_data
      Convert response body into an RFC2397 data URL

      mod_ratelimit
      Provides Bandwidth Rate Limiting for Clients

      mod_request
      Provides Filters to handle and make available HTTP request bodies

      mod_reflector
      Provides Reflection of a request body as a response via the output filter stack.

      mod_slotmem_shm
      Provides a Slot-based shared memory provider (ala the scoreboard).

      mod_xml2enc
      Formerly a third-party module, this supports internationalisation
      in libxml2-based (markup-aware) filter modules.

      mod_macro (available since 2.4.5)
      Provide macros within configuration files.

      mod_proxy_wstunnel (available since 2.4.5)
      Support web-socket tunnels.

      mod_authnz_fcgi (available since 2.4.10)
      Enable FastCGI authorizer applications to authenticate and/or
      authorize clients.

      mod_http2 (available since 2.4.17)
      Support for the HTTP/2 transport layer.

      mod_proxy_http2 (available since 2.4.19)
      HTTP/2 Protocol backend for mod_proxy

      mod_proxy_hcheck (available since 2.4.21)
      Support independent dynamic health checks for remote proxiy backend servers.

      mod_brotli (available since 2.4.26)
      Support the Brotli compression algorithm.

      mod_md (available since 2.4.30)
      Support the ACME protocol to automate certificate provisionning.

      mod_proxy_uwsgi (available since 2.4.30)
      UWSGI gateway module for mod_proxy.

      mod_socache_redis (available since 2.4.39)
      Support Redis based shared object cache provider.

      mod_systemd (available since 2.4.42)
      systemd integration. It allows httpd to be used in a service with the systemd
      Type=notify.

    
  

Module Enhancements
    
    
      mod_ssl

      mod_ssl 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.

      mod_ssl 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. 

      mod_ssl can now be configured to share SSL Session
      data between servers through memcached

      EC keys are now supported in addition to RSA and DSA.

      Support for TLS-SRP (available in 2.4.4 and later).

      mod_proxy

      The ProxyPass directive
      is now most optimally configured within a
      Location or
      LocationMatch
      block, and offers a significant performance advantage over the traditional
      two-parameter syntax when present in large numbers.
      The source address used for proxy requests is now configurable.
      Support for Unix domain sockets to the backend (available in 2.4.7
      and later).

      mod_proxy_balancer

      More runtime configuration changes for BalancerMembers via balancer-manager

      Additional BalancerMembers can be added at runtime via balancer-manager

      Runtime configuration of a subset of Balancer parameters

      BalancerMembers can be set to 'Drain' so that they only respond to existing sticky
      sessions, allowing them to be taken gracefully offline.

      Balancer settings can be persistent after restarts.

      mod_cache

      The mod_cache CACHE filter can be optionally inserted
      at a given point in the filter chain to provide fine control over caching.
      

      mod_cache can now cache HEAD requests.

      Where possible, mod_cache directives can now be set
      per directory, instead of per server.

      The base URL of cached URLs can be customised, so that a cluster of
      caches can share the same endpoint URL prefix.

      mod_cache is now capable of serving stale cached
      data when a backend is unavailable (error 5xx).

      mod_cache can now insert HIT/MISS/REVALIDATE into
      an X-Cache header.

      mod_include
      Support for the 'onerror' attribute within an 'include' element,
      allowing an error document to be served on error instead of the default
      error string.

      mod_cgi, mod_include,
          mod_isapi, ...
      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. Environment Variables
      in Apache has some pointers on how to work around broken legacy
      clients which require such headers. (This affects all modules which
      use these environment variables.)

      mod_authz_core Authorization Logic Containers

      Advanced authorization logic may now be specified using the
          Require directive
          and the related container directives, such as
          <RequireAll>.

      mod_rewrite
      mod_rewrite adds the [QSD]
          (Query String Discard) and [END] flags for
          RewriteRule to
          simplify common rewriting scenarios.
      Adds the possibility to use complex boolean expressions in RewriteCond.
      Allows the use of SQL queries as RewriteMap functions.

      mod_ldap, mod_authnz_ldap
      mod_authnz_ldap adds support for nested groups.
      mod_ldap adds
          LDAPConnectionPoolTTL,
          LDAPTimeout, 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.
      mod_ldap adds
          LDAPLibraryDebug to log
          debug information provided by the used LDAP toolkit.

      mod_info
      mod_info can now dump the pre-parsed configuration
          to stdout during server startup.

      mod_auth_basic
      New generic mechanism to fake basic authentication (available in
      2.4.5 and later).

    
  

Program Enhancements
    
    
        fcgistarter
        New FastCGI daemon starter utility

        htcacheclean
        Current cached URLs can now be listed, with optional metadata
        included.
        Allow explicit deletion of individual cached URLs from the
        cache.
        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.
        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.

        rotatelogs
        May now create a link to the current log file.
        May now invoke a custom post-rotate script.

        htpasswd, htdbm
        Support for the bcrypt algorithm (available in 2.4.4 and later).
        
    
  

Documentation
    
    
        mod_rewrite
        The mod_rewrite 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 Rewrite
        Guide is now a top-level section with much more detail and
        better organization.

        mod_ssl
        The mod_ssl documentation has been greatly
        enhanced, with more examples at the getting started level, in
        addition to the previous focus on technical details.

        Caching Guide
        The Caching Guide has been rewritten
        to properly distinguish between the RFC2616 HTTP/1.1 caching
        features provided by mod_cache, and the generic
        key/value caching provided by the socache
        interface, as well as to cover specialised caching provided by
        mechanisms such as mod_file_cache.

    
  

Module Developer Changes
    
    
      Check Configuration Hook Added

      A new hook, check_config, has been added which runs
          between the pre_config and open_logs
          hooks.  It also runs before the test_config hook
          when the -t option is passed to
          httpd.  The check_config 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 open_logs hook function redirects
          console output to the error log.

      Expression Parser Added

      We now have a general-purpose expression parser, whose API is
          exposed in ap_expr.h.  This is adapted from the
          expression parser previously implemented in
          mod_ssl.

      Authorization Logic Containers

      Authorization modules now register as a provider, via
      ap_register_auth_provider(), to support advanced authorization logic,
      such as <RequireAll>.

      Small-Object Caching Interface

      The ap_socache.h header exposes a provider-based
      interface for caching small data objects, based on the previous
      implementation of the mod_ssl session cache.
      Providers using a shared-memory cyclic buffer, disk-based dbm
      files, and a memcache distributed cache are currently
      supported.

      Cache Status Hook Added

      The mod_cache module now includes a new
      cache_status hook, which is called when the caching
      decision becomes known. A default implementation is provided
      which adds an optional X-Cache and
      X-Cache-Detail header to the response.
    

    The developer documentation contains a
    detailed list of API changes.
  

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