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
- 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
- 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
- Per-module and per-directory LogLevel configuration
LogLevel can now be
configured per module and per directory. New levels
trace8 have been added above the
- Per-request configuration sections
sections can be used to set the configuration based on per-request
- General-purpose expression parser
- A new expression parser allows to specify
complex conditions using a common syntax
in directives like
- 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
directive allows more fine grained control which directives are
- Config file variables
- It is now possible to
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
- FastCGI Protocol backend for
- SCGI Protocol backend for
- Provides dynamically configured mass reverse proxies for
- 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_proxy_balancer to base loadbalancing decisions
on the number of active connections on the backend servers.
- 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.
- An advanced replacement of
to edit the response body with the full power of sed.
- Enables form-based authentication.
- Enables the use of session state for clients, using cookie or
- New module to restrict certain HTTP methods without interfering with
authentication or authorization.
- Embeds the Lua language into httpd,
for configuration and small business logic functions. (Experimental)
- Allows the addition of customizable debug logging at different phases of the
- Provides for buffering the input and output filter stacks
- Convert response body into an RFC2397 data URL
- Provides Bandwidth Rate Limiting for Clients
- Provides Filters to handle and make available HTTP request bodies
- Provides Reflection of a request body as a response via the output filter stack.
- Provides a Slot-based shared memory provider (ala the scoreboard).
- 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
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_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_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
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).
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.
- The source address used for proxy requests is now configurable.
- Support for Unix domain sockets to the backend (available in 2.4.7
- 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 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.
- Support for the 'onerror' attribute within an 'include' element,
allowing an error document to be served on error instead of the default
- 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
and the related container directives, such as
mod_rewrite adds the
(Query String Discard) and
[END] flags for
simplify common rewriting scenarios.
- Adds the possibility to use complex boolean expressions in
- Allows the use of SQL queries as
mod_authnz_ldap adds support for nested groups.
other improvements in the handling of timeouts.
This is especially useful for setups where a
stateful firewall drops idle connections to the LDAP server.
LDAPLibraryDebug to log
debug information provided by the used LDAP toolkit.
mod_info can now dump the pre-parsed configuration
to stdout during server startup.
- New generic mechanism to fake basic authentication (available in
2.4.5 and later).
- New FastCGI daemon starter utility
- Current cached URLs can now be listed, with optional metadata
- Allow explicit deletion of individual cached URLs from the
- 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
- May now create a link to the current log file.
- May now invoke a custom post-rotate script.
- Support for the bcrypt algorithm (available in 2.4.4 and later).
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
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
- Check Configuration Hook Added
- A new hook,
check_config, has been added which runs
hooks. It also runs before the
-t option is passed to
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
- Authorization Logic Containers
- Authorization modules now register as a provider, via
ap_register_auth_provider(), to support advanced authorization logic,
- 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
- Cache Status Hook Added
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-Detail header to the response.
The developer documentation contains a
detailed list of API changes.