Apache HTTP Server Version 2.4
Description: | Multi-protocol proxy/gateway server |
---|---|
Status: | Extension |
Module Identifier: | proxy_module |
Source File: | mod_proxy.c |
Do not enable proxying with ProxyRequests
until you have secured your server. Open proxy servers are dangerous both to your
network and to the Internet at large.
mod_proxy
and related modules implement a
proxy/gateway for Apache HTTP Server, supporting a number of popular
protocols as well as several different load balancing algorithms.
Third-party modules can add support for additional protocols and
load balancing algorithms.
A set of modules must be loaded into the server to provide the
necessary features. These modules can be included statically at
build time or dynamically via the
LoadModule
directive).
The set must include:
mod_proxy
, which provides basic proxy
capabilitiesmod_proxy_balancer
and one or more
balancer modules if load balancing is required. (See
mod_proxy_balancer
for more information.)Protocol | Module |
---|---|
AJP13 (Apache JServe Protocol version 1.3) | mod_proxy_ajp |
CONNECT (for SSL) | mod_proxy_connect |
FastCGI | mod_proxy_fcgi |
ftp | mod_proxy_ftp |
HTTP/0.9, HTTP/1.0, and HTTP/1.1 | mod_proxy_http |
HTTP/2.0 | mod_proxy_http2 |
SCGI | mod_proxy_scgi |
UWSGI | mod_proxy_uwsgi |
WS and WSS (Web-sockets) | mod_proxy_wstunnel |
In addition, extended features are provided by other modules.
Caching is provided by mod_cache
and related
modules. The ability to contact remote servers using the SSL/TLS
protocol is provided by the SSLProxy*
directives of
mod_ssl
. These additional modules will need
to be loaded and configured to take advantage of these features.
Apache HTTP Server can be configured in both a forward and reverse proxy (also known as gateway) mode.
An ordinary forward proxy is an intermediate server that sits between the client and the origin server. In order to get content from the origin server, the client sends a request to the proxy naming the origin server as the target. The proxy then requests the content from the origin server and returns it to the client. The client must be specially configured to use the forward proxy to access other sites.
A typical usage of a forward proxy is to provide Internet
access to internal clients that are otherwise restricted by a
firewall. The forward proxy can also use caching (as provided
by mod_cache
) to reduce network usage.
The forward proxy is activated using the ProxyRequests
directive. Because
forward proxies allow clients to access arbitrary sites through
your server and to hide their true origin, it is essential that
you secure your server so that only
authorized clients can access the proxy before activating a
forward proxy.
A reverse proxy (or gateway), by contrast, appears to the client just like an ordinary web server. No special configuration on the client is necessary. The client makes ordinary requests for content in the namespace of the reverse proxy. The reverse proxy then decides where to send those requests and returns the content as if it were itself the origin.
A typical usage of a reverse proxy is to provide Internet users access to a server that is behind a firewall. Reverse proxies can also be used to balance load among several back-end servers or to provide caching for a slower back-end server. In addition, reverse proxies can be used simply to bring several servers into the same URL space.
A reverse proxy is activated using the ProxyPass
directive or the
[P]
flag to the RewriteRule
directive. It is
not necessary to turn ProxyRequests
on in order to
configure a reverse proxy.
The examples below are only a very basic idea to help you get started. Please read the documentation on the individual directives.
In addition, if you wish to have caching enabled, consult
the documentation from mod_cache
.
ProxyPass "/foo" "http://foo.example.com/bar" ProxyPassReverse "/foo" "http://foo.example.com/bar"
ProxyRequests On ProxyVia On <Proxy "*"> Require host internal.example.com </Proxy>
You can also force a request to be handled as a reverse-proxy request, by creating a suitable Handler pass-through. The example configuration below will pass all requests for PHP scripts to the specified FastCGI server using reverse proxy:
<FilesMatch "\.php$"> # Unix sockets require 2.4.7 or later SetHandler "proxy:unix:/path/to/app.sock|fcgi://localhost/" </FilesMatch>
This feature is available in Apache HTTP Server 2.4.10 and later.
The proxy manages the configuration of origin servers and their communication parameters in objects called workers. There are two built-in workers: the default forward proxy worker and the default reverse proxy worker. Additional workers can be configured explicitly.
The two default workers have a fixed configuration and will be used if no other worker matches the request. They do not use HTTP Keep-Alive or connection reuse. The TCP connections to the origin server will instead be opened and closed for each request.
Explicitly configured workers are identified by their URL.
They are usually created and configured using
ProxyPass
or
ProxyPassMatch
when used
for a reverse proxy:
ProxyPass "/example" "http://backend.example.com" connectiontimeout=5 timeout=30
This will create a worker associated with the origin server URL
http://backend.example.com
that will use the given timeout
values. When used in a forward proxy, workers are usually defined
via the ProxySet
directive:
ProxySet "http://backend.example.com" connectiontimeout=5 timeout=30
or alternatively using Proxy
and ProxySet
:
<Proxy "http://backend.example.com"> ProxySet connectiontimeout=5 timeout=30 </Proxy>
Using explicitly configured workers in the forward mode is
not very common, because forward proxies usually communicate with many
different origin servers. Creating explicit workers for some of the
origin servers can still be useful if they are used very often.
Explicitly configured workers have no concept of forward or reverse
proxying by themselves. They encapsulate a common concept of
communication with origin servers. A worker created by
ProxyPass
for use in a
reverse proxy will also be used for forward proxy requests whenever
the URL to the origin server matches the worker URL, and vice versa.
The URL identifying a direct worker is the URL of its origin server including any path components given:
ProxyPass "/examples" "http://backend.example.com/examples" ProxyPass "/docs" "http://backend.example.com/docs"
This example defines two different workers, each using a separate connection pool and configuration.
Worker sharing happens if the worker URLs overlap, which occurs when the URL of some worker is a leading substring of the URL of another worker defined later in the configuration file. In the following example
ProxyPass "/apps" "http://backend.example.com/" timeout=60 ProxyPass "/examples" "http://backend.example.com/examples" timeout=10
the second worker isn't actually created. Instead the first
worker is used. The benefit is, that there is only one connection pool,
so connections are more often reused. Note that all configuration attributes
given explicitly for the later worker will be ignored. This will be logged
as a warning. In the above example, the resulting timeout value
for the URL /examples
will be 60
instead
of 10
!
If you want to avoid worker sharing, sort your worker definitions
by URL length, starting with the longest worker URLs. If you want to maximize
worker sharing, use the reverse sort order. See also the related warning about
ordering ProxyPass
directives.
Explicitly configured workers come in two flavors:
direct workers and (load) balancer workers.
They support many important configuration attributes which are
described below in the ProxyPass
directive. The same attributes can also be set using
ProxySet
.
The set of options available for a direct worker
depends on the protocol which is specified in the origin server URL.
Available protocols include ajp
, fcgi
,
ftp
, http
and scgi
.
Balancer workers are virtual workers that use direct workers known as their members to actually handle the requests. Each balancer can have multiple members. When it handles a request, it chooses a member based on the configured load balancing algorithm.
A balancer worker is created if its worker URL uses
balancer
as the protocol scheme.
The balancer URL uniquely identifies the balancer worker.
Members are added to a balancer using
BalancerMember
.
DNS resolution happens when the socket to
the origin domain is created for the first time.
When connection reuse is enabled, each backend domain is resolved
only once per child process, and cached for all further connections
until the child is recycled. This information should to be considered
while planning DNS maintenance tasks involving backend domains.
Please also check ProxyPass
parameters for more details about connection reuse.
You can control who can access your proxy via the <Proxy>
control block as in
the following example:
<Proxy "*"> Require ip 192.168.0 </Proxy>
For more information on access control directives, see
mod_authz_host
.
Strictly limiting access is essential if you are using a
forward proxy (using the ProxyRequests
directive).
Otherwise, your server can be used by any client to access
arbitrary hosts while hiding his or her true identity. This is
dangerous both for your network and for the Internet at large.
When using a reverse proxy (using the ProxyPass
directive with
ProxyRequests Off
), access control is less
critical because clients can only contact the hosts that you
have specifically configured.
See Also the Proxy-Chain-Auth environment variable.
If you're using the ProxyBlock
directive, hostnames' IP addresses are looked up
and cached during startup for later match test. This may take a few
seconds (or more) depending on the speed with which the hostname lookups
occur.
An Apache httpd proxy server situated in an intranet needs to forward
external requests through the company's firewall (for this, configure
the ProxyRemote
directive
to forward the respective scheme to the firewall proxy).
However, when it has to
access resources within the intranet, it can bypass the firewall when
accessing hosts. The NoProxy
directive is useful for specifying which hosts belong to the intranet and
should be accessed directly.
Users within an intranet tend to omit the local domain name from their
WWW requests, thus requesting "http://somehost/" instead of
http://somehost.example.com/
. Some commercial proxy servers
let them get away with this and simply serve the request, implying a
configured local domain. When the ProxyDomain
directive is used and the server is configured for proxy service, Apache httpd can return
a redirect response and send the client to the correct, fully qualified,
server address. This is the preferred method since the user's bookmark
files will then contain fully qualified hosts.
For circumstances where mod_proxy
is sending
requests to an origin server that doesn't properly implement
keepalives or HTTP/1.1, there are two environment variables that can force the
request to use HTTP/1.0 with no keepalive. These are set via the
SetEnv
directive.
These are the force-proxy-request-1.0
and
proxy-nokeepalive
notes.
<Location "/buggyappserver/"> ProxyPass "http://buggyappserver:7001/foo/" SetEnv force-proxy-request-1.0 1 SetEnv proxy-nokeepalive 1 </Location>
In 2.4.26 and later, the "no-proxy" environment variable can be set to disable
mod_proxy
processing the current request.
This variable should be set with SetEnvIf
, as SetEnv
is not evaluated early enough.
Some request methods such as POST include a request body.
The HTTP protocol requires that requests which include a body
either use chunked transfer encoding or send a
Content-Length
request header. When passing these
requests on to the origin server, mod_proxy_http
will always attempt to send the Content-Length
. But
if the body is large and the original request used chunked
encoding, then chunked encoding may also be used in the upstream
request. You can control this selection using environment variables. Setting
proxy-sendcl
ensures maximum compatibility with
upstream servers by always sending the
Content-Length
, while setting
proxy-sendchunked
minimizes resource usage by using
chunked encoding.
Under some circumstances, the server must spool request bodies to disk to satisfy the requested handling of request bodies. For example, this spooling will occur if the original body was sent with chunked encoding (and is large), but the administrator has asked for backend requests to be sent with Content-Length or as HTTP/1.0. This spooling can also occur if the request body already has a Content-Length header, but the server is configured to filter incoming request bodies.
LimitRequestBody
only applies to
request bodies that the server will spool to disk
When acting in a reverse-proxy mode (using the ProxyPass
directive, for example),
mod_proxy_http
adds several request headers in
order to pass information to the origin server. These headers
are:
X-Forwarded-For
X-Forwarded-Host
Host
HTTP request header.X-Forwarded-Server
Be careful when using these headers on the origin server, since
they will contain more than one (comma-separated) value if the
original request already contained one of these headers. For
example, you can use %{X-Forwarded-For}i
in the log
format string of the origin server to log the original clients IP
address, but you may get more than one address if the request
passes through several proxies.
See also the ProxyPreserveHost
and ProxyVia
directives, which control
other request headers.
Note: If you need to specify custom request headers to be
added to the forwarded request, use the
RequestHeader
directive.
Description: | Number of additional Balancers that can be added Post-configuration |
---|---|
Syntax: | BalancerGrowth # |
Default: | BalancerGrowth 5 |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | BalancerGrowth is only available in Apache HTTP Server 2.3.13 and later. |
This directive allows for growth potential in the number of Balancers available for a virtualhost in addition to the number pre-configured. It only takes effect if there is at least one pre-configured Balancer.
Description: | Inherit ProxyPassed Balancers/Workers from the main server |
---|---|
Syntax: | BalancerInherit On|Off |
Default: | BalancerInherit On |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | BalancerInherit is only available in Apache HTTP Server 2.4.5 and later. |
This directive will cause the current server/vhost to "inherit" ProxyPass Balancers and Workers defined in the main server. This can cause issues and inconsistent behavior if using the Balancer Manager and so should be disabled if using that feature.
The setting in the global server defines the default for all vhosts.
Description: | Add a member to a load balancing group |
---|---|
Syntax: | BalancerMember [balancerurl] url [key=value [key=value ...]] |
Context: | directory |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | BalancerMember is only available in Apache HTTP Server 2.2 and later. |
This directive adds a member to a load balancing group. It can be used
within a <Proxy balancer://...>
container
directive and can take any of the key value pair parameters available to
ProxyPass
directives.
One additional parameter is available only to BalancerMember
directives:
loadfactor. This is the member load factor - a decimal number between 1.0
(default) and 100.0, which defines the weighted load to be applied to the
member in question.
The balancerurl is only needed when not within a
<Proxy balancer://...>
container directive. It corresponds to the url of a balancer defined in
ProxyPass
directive.
The path component of the balancer URL in any
<Proxy balancer://...>
container directive
is ignored.
Trailing slashes should typically be removed from the URL of a
BalancerMember
.
Description: | Attempt to persist changes made by the Balancer Manager across restarts. |
---|---|
Syntax: | BalancerPersist On|Off |
Default: | BalancerPersist Off |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | BalancerPersist is only available in Apache HTTP Server 2.4.4 and later. |
This directive will cause the shared memory storage associated with the balancers and balancer members to be persisted across restarts. This allows these local changes to not be lost during the normal restart/graceful state transitions.
Description: | Hosts, domains, or networks that will be connected to directly |
---|---|
Syntax: | NoProxy host [host] ... |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
This directive is only useful for Apache httpd proxy servers within
intranets. The NoProxy
directive specifies a
list of subnets, IP addresses, hosts and/or domains, separated by
spaces. A request to a host which matches one or more of these is
always served directly, without forwarding to the configured
ProxyRemote
proxy server(s).
ProxyRemote "*" "http://firewall.example.com:81" NoProxy ".example.com" "192.168.112.0/21"
The host arguments to the NoProxy
directive are one of the following type list:
A Domain is a partially qualified DNS domain name, preceded by a period. It represents a list of hosts which logically belong to the same DNS domain or zone (i.e., the suffixes of the hostnames are all ending in Domain).
.com .example.org.
To distinguish Domains from Hostnames (both syntactically and semantically; a DNS domain can have a DNS A record, too!), Domains are always written with a leading period.
Domain name comparisons are done without regard to the case, and
Domains are always assumed to be anchored in the root of the
DNS tree; therefore, the two domains .ExAmple.com
and
.example.com.
(note the trailing period) are considered
equal. Since a domain comparison does not involve a DNS lookup, it is much
more efficient than subnet comparison.
A SubNet is a partially qualified internet address in numeric (dotted quad) form, optionally followed by a slash and the netmask, specified as the number of significant bits in the SubNet. It is used to represent a subnet of hosts which can be reached over a common network interface. In the absence of the explicit net mask it is assumed that omitted (or zero valued) trailing digits specify the mask. (In this case, the netmask can only be multiples of 8 bits wide.) Examples:
192.168
or 192.168.0.0
255.255.0.0
)192.168.112.0/21
192.168.112.0/21
with a netmask of 21
valid bits (also used in the form 255.255.248.0
)As a degenerate case, a SubNet with 32 valid bits is the equivalent to an IPAddr, while a SubNet with zero valid bits (e.g., 0.0.0.0/0) is the same as the constant _Default_, matching any IP address.
A IPAddr represents a fully qualified internet address in numeric (dotted quad) form. Usually, this address represents a host, but there need not necessarily be a DNS domain name connected with the address.
192.168.123.7
An IPAddr does not need to be resolved by the DNS system, so it can result in more effective apache performance.
A Hostname is a fully qualified DNS domain name which can be resolved to one or more IPAddrs via the DNS domain name service. It represents a logical host (in contrast to Domains, see above) and must be resolvable to at least one IPAddr (or often to a list of hosts with different IPAddrs).
prep.ai.example.edu
www.example.org
In many situations, it is more effective to specify an IPAddr in place of a Hostname since a DNS lookup can be avoided. Name resolution in Apache httpd can take a remarkable deal of time when the connection to the name server uses a slow PPP link.
Hostname comparisons are done without regard to the case,
and Hostnames are always assumed to be anchored in the root
of the DNS tree; therefore, the two hosts WWW.ExAmple.com
and www.example.com.
(note the trailing period) are
considered equal.
Description: | Container for directives applied to proxied resources |
---|---|
Syntax: | <Proxy wildcard-url> ...</Proxy> |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
Directives placed in <Proxy>
sections apply only to matching proxied content. Shell-style wildcards are
allowed.
For example, the following will allow only hosts in
yournetwork.example.com
to access content via your proxy
server:
<Proxy "*"> Require host yournetwork.example.com </Proxy>
The following example will process all files in the foo
directory of example.com
through the INCLUDES
filter when they are sent through the proxy server:
<Proxy "http://example.com/foo/*"> SetOutputFilter INCLUDES </Proxy>
A backend URL matches the configuration section if it begins with the
the wildcard-url string, even if the last path segment in the
directive only matches a prefix of the backend URL. For example,
<Proxy "http://example.com/foo"> matches all of
http://example.com/foo, http://example.com/foo/bar, and
http://example.com/foobar. The matching of the final URL differs
from the behavior of the <Location>
section, which for purposes of this note
treats the final path component as if it ended in a slash.
For more control over the matching, see <ProxyMatch>
.
Description: | Forward 100-continue expectation to the origin server |
---|---|
Syntax: | Proxy100Continue Off|On |
Default: | Proxy100Continue On |
Context: | server config, virtual host, directory |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | Available in version 2.4.40 and later |
This directive determines whether the proxy should forward 100-continue
Expect:ation to the origin server and thus let it decide when/if
the HTTP request body should be read, or when Off
the proxy
should generate 100 Continue intermediate response by itself before
forwarding the request body.
This option is of use only for HTTP proxying, as handled by mod_proxy_http
.
Description: | Add proxy information in X-Forwarded-* headers |
---|---|
Syntax: | ProxyAddHeaders Off|On |
Default: | ProxyAddHeaders On |
Context: | server config, virtual host, directory |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | Available in version 2.3.10 and later |
This directive determines whether or not proxy related information should be passed to the backend server through X-Forwarded-For, X-Forwarded-Host and X-Forwarded-Server HTTP headers.
This option is of use only for HTTP proxying, as handled by mod_proxy_http
.
Description: | Determines how to handle bad header lines in a response |
---|---|
Syntax: | ProxyBadHeader IsError|Ignore|StartBody |
Default: | ProxyBadHeader IsError |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
The ProxyBadHeader
directive determines the
behavior of mod_proxy
if it receives syntactically invalid
response header lines (i.e. containing no colon) from the origin
server. The following arguments are possible:
IsError
Ignore
StartBody
Description: | Words, hosts, or domains that are banned from being proxied |
---|---|
Syntax: | ProxyBlock *|word|host|domain
[word|host|domain] ... |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
The ProxyBlock
directive specifies a list of
words, hosts and/or domains, separated by spaces. HTTP, HTTPS, and
FTP document requests to sites whose names contain matched words,
hosts or domains are blocked by the proxy server. The proxy
module will also attempt to determine IP addresses of list items which
may be hostnames during startup, and cache them for match test as
well. That may slow down the startup time of the server.
ProxyBlock "news.example.com" "auctions.example.com" "friends.example.com"
Note that example
would also be sufficient to match any
of these sites.
Hosts would also be matched if referenced by IP address.
Note also that
ProxyBlock "*"
blocks connections to all sites.
Description: | Default domain name for proxied requests |
---|---|
Syntax: | ProxyDomain Domain |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
This directive is only useful for Apache httpd proxy servers within
intranets. The ProxyDomain
directive specifies
the default domain which the apache proxy server will belong to. If a
request to a host without a domain name is encountered, a redirection
response to the same host with the configured Domain appended
will be generated.
ProxyRemote "*" "http://firewall.example.com:81" NoProxy ".example.com" "192.168.112.0/21" ProxyDomain ".example.com"
Description: | Override error pages for proxied content |
---|---|
Syntax: | ProxyErrorOverride Off|On [code ...] |
Default: | ProxyErrorOverride Off |
Context: | server config, virtual host, directory |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | The list of status codes was added in 2.5.1 |
This directive is useful for reverse-proxy setups where you want to
have a common look and feel on the error pages seen by the end user.
This also allows for included files (via
mod_include
's SSI) to get
the error code and act accordingly. (Default behavior would display
the error page of the proxied server. Turning this on shows the SSI
Error message.)
This directive does not affect the processing of informational (1xx), normal success (2xx), or redirect (3xx) responses.
By default ProxyErrorOverride
affects all responses with codes between 400 (including)
and 600 (excluding).
ProxyErrorOverride On
To change the default behavior, you can specify the status codes to consider, separated by spaces. If you do so, all other status codes will be ignored. You can only specify status codes, that are considered error codes: between 400 (including) and 600 (excluding).
ProxyErrorOverride On 403 405 500 501 502 503 504
Description: | Determine size of internal data throughput buffer |
---|---|
Syntax: | ProxyIOBufferSize bytes |
Default: | ProxyIOBufferSize 8192 |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
The ProxyIOBufferSize
directive adjusts the size
of the internal buffer which is used as a scratchpad for the data between
input and output. The size must be at least 512
.
In almost every case, there's no reason to change that value.
If used with AJP, this directive sets the maximum AJP packet size in
bytes. Values larger than 65536 are set to 65536. If you change it from
the default, you must also change the packetSize
attribute of
your AJP connector on the Tomcat side! The attribute
packetSize
is only available in Tomcat 5.5.20+
and 6.0.2+
Normally it is not necessary to change the maximum packet size. Problems with the default value have been reported when sending certificates or certificate chains.
Description: | Container for directives applied to regular-expression-matched proxied resources |
---|---|
Syntax: | <ProxyMatch regex> ...</ProxyMatch> |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
The <ProxyMatch>
directive is
identical to the <Proxy>
directive, except that it matches URLs
using regular expressions.
From 2.4.8 onwards, named groups and backreferences are captured and
written to the environment with the corresponding name prefixed with
"MATCH_" and in upper case. This allows elements of URLs to be referenced
from within expressions and modules like
mod_rewrite
. In order to prevent confusion, numbered
(unnamed) backreferences are ignored. Use named groups instead.
<ProxyMatch "^http://(?<sitename>[^/]+)"> Require ldap-group cn=%{env:MATCH_SITENAME},ou=combined,o=Example </ProxyMatch>
Description: | Maximum number of proxies that a request can be forwarded through |
---|---|
Syntax: | ProxyMaxForwards number |
Default: | ProxyMaxForwards -1 |
Context: | server config, virtual host |
Status: | Extension |
Module: | mod_proxy |
Compatibility: | Default behaviour changed in 2.2.7 |
The ProxyMaxForwards
directive specifies the
maximum number of proxies through which a request may pass if there's no
Max-Forwards
header supplied with the request. This may
be set to prevent infinite proxy loops or a DoS attack.
ProxyMaxForwards 15
Note that setting ProxyMaxForwards
is a
violation of the