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Apache > HTTP Server > Documentation > Version 2.4

Overview 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.

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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.
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.
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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.
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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.
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.
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