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Apache HTTP Server Version 2.0
Apache Module mod_proxy
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Summary
Warning
This document has been updated to take into account changes made in the 2.0 version of the Apache HTTP Server. Some of the information may still be inaccurate, please use it with care.
This module implements a proxy/gateway for Apache. It implements
proxying capability for
FTP,
CONNECT (for SSL),
HTTP/0.9,
HTTP/1.0, and
HTTP/1.1.
The module can be configured to connect to other proxy modules for these
and other protocols.
This module was experimental in Apache 1.1.x. Improvements and bugfixes were made in Apache v1.2.x and Apache v1.3.x, then the module underwent a major overhaul for Apache v2.0. The protocol support was upgraded to HTTP/1.1, and filter support was enabled.
Please note that the caching function present in mod_proxy up to Apache v1.3.x has been removed from mod_proxy and will be incorporated into a new module, mod_cache.
Do not enable proxying with
ProxyRequestsuntil you have secured your server. Open proxy servers are dangerous both to your network and to the Internet at large.
Directives
- AllowCONNECT
- NoProxy
- Proxy
- ProxyBlock
- ProxyDomain
- ProxyErrorOverride
- ProxyIOBufferSize
- ProxyMatch
- ProxyMaxForwards
- ProxyPass
- ProxyPassReverse
- ProxyPreserveHost
- ProxyReceiveBufferSize
- ProxyRemote
- ProxyRemoteMatch
- ProxyRequests
- ProxyTimeout
- ProxyVia
Common configuration topics
- Forward and Reverse Proxies
- Controlling access to your proxy
- Using Netscape hostname shortcuts
- Why doesn't file type xxx download via FTP?
- How can I force an FTP ASCII download of File xxx?
- How can I access FTP files outside of my home directory?
- How can I hide the FTP cleartext password in my browser's URL line?
- Why does Apache start more slowly when using the proxy module?
- What other functions are useful for an intranet proxy server?
- How can I make the proxy talk HTTP/1.0 and disable keepalives?
Forward and Reverse Proxies
Apache can be configured in both a forward and reverse proxy configuration.
A forward proxy is an intermediate system that enables a browser to connect to a remote network to which it normally does not have access. A forward proxy can also be used to cache data, reducing load on the networks between the forward proxy and the remote webserver.
Apache's mod_proxy can be figured to behave like a forward proxy
using the ProxyRemote
directive. In addition, caching of data can be achieved by configuring
Apache mod_cache. Other dedicated forward proxy
packages include Squid.
A reverse proxy is a webserver system that is capable of serving webpages sourced from other webservers - in addition to webpages on disk or generated dynamically by CGI - making these pages look like they originated at the reverse proxy.
When configured with the mod_cache module the reverse proxy can act as a cache for slower backend webservers. The reverse proxy can also enable advanced URL strategies and management techniques, allowing webpages served using different webserver systems or architectures to coexist inside the same URL space. Reverse proxy systems are also ideal for implementing centralised logging websites with many or diverse website backends. Complex multi-tier webserver systems can be constructed using an Apache mod_proxy frontend and any number of backend webservers.
The reverse proxy is configured using the
ProxyPass and ProxyPassReverse directives. Caching can be
enabled using mod_cache as with the forward proxy.
Controlling access to your proxy
You can control who can access your proxy via the
<Proxy>
control block using the following example:
<Proxy *>
Order Deny,Allow
Deny from all
Allow from 192.168.0
</Proxy>
When configuring a reverse proxy, access control takes on the
attributes of the normal server <directory> configuration.
Why doesn't file type xxx download via FTP?
You probably don't have that particular file type defined as application/octet-stream in your proxy's mime.types configuration file. A useful line can be
application/octet-stream bin dms lha lzh exe class tgz taz
How can I force an FTP ASCII download of File xxx?
In the rare situation where you must download a specific file using the FTP
ASCII transfer method (while the default transfer is in
binary mode), you can override mod_proxy's default by
suffixing the request with ;type=a to force an ASCII transfer.
(FTP Directory listings are always executed in ASCII mode, however.)
How can I access FTP files outside of my home directory?
An FTP URI is interpreted relative to the home directory of the user who is logging in. Alas, to reach higher directory levels you cannot use /../, as the dots are interpreted by the browser and not actually sent to the FTP server. To address this problem, the so called "Squid %2f hack" was implemented in the Apache FTP proxy; it is is a solution which is also used by other popular proxy servers like the Squid Proxy Cache. By prepending /%2f to the path of your request, you can make such a proxy change the FTP starting directory to / (instead of the home directory).
Example: To retrieve the file
/etc/motd, you would use the URL
ftp://user@host/%2f/etc/motd
How can I hide the FTP cleartext password in my browser's URL line?
To log in to an FTP server by username and password, Apache uses different strategies. In absense of a user name and password in the URL altogether, Apache sends an anomymous login to the FTP server, i.e.,
user: anonymous
password: apache_proxy@
This works for all popular FTP servers which are configured for anonymous access.
For a personal login with a specific username, you can embed
the user name into the URL, like in:
ftp://username@host/myfile. If the FTP server
asks for a password when given this username (which it should),
then Apache will reply with a [401 Authorization required] response,
which causes the Browser to pop up the username/password dialog.
Upon entering the password, the connection attempt is retried,
and if successful, the requested resource is presented.
The advantage of this procedure is that your browser does not
display the password in cleartext (which it would if you had used
ftp://username:password@host/myfile in
the first place).
Note
The password which is transmitted in such a way is not encrypted on its way. It travels between your browser and the Apache proxy server in a base64-encoded cleartext string, and between the Apache proxy and the FTP server as plaintext. You should therefore think twice before accessing your FTP server via HTTP (or before accessing your personal files via FTP at all!) When using unsecure channels, an eavesdropper might intercept your password on its way.
Why does Apache start more slowly when using the proxy module?
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.
What other functions are useful for an intranet proxy server?
An Apache proxy server situated in an intranet needs to forward
external requests through the company's firewall. 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.my.dom.ain/". 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 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.
How can I make the proxy talk HTTP/1.0 and disable keepalives?
For circumstances where you have a application server which doesn't implement
keepalives or HTTP/1.1 properly, there are 2 environment variables which when
set send a 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>
AllowCONNECT Directive
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The AllowCONNECT directive specifies a list
of port numbers to which the proxy CONNECT method may
connect. Today's browsers use this method when a https
connection is requested and proxy tunneling over http is in
effect.
By default, only the default https port (443) and the
default snews port (563) are enabled. Use the
AllowCONNECT directive to overrride this default and
allow connections to the listed ports only.
NoProxy Directive
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This directive is only useful for Apache 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).
Example
ProxyRemote * http://firewall.mycompany.com:81
NoProxy .mycompany.com 192.168.112.0/21
The arguments to the NoProxy directive are one of the following type list:
- Domain
- 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).
Examples:.com.apache.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.
Note: 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 two domains.MyDomain.comand.mydomain.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. - SubNet
- 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:192.168or192.168.0.0- the subnet 192.168.0.0 with an implied netmask of 16 valid bits
(sometimes used in the netmask form
255.255.0.0) 192.168.112.0/21- the subnet
192.168.112.0/21with a netmask of 21 valid bits (also used in the form 255.255.248.0)
- IPAddr
- 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.
Example: 192.168.123.7
Note: An IPAddr does not need to be resolved by the DNS system, so it can result in more effective apache performance. - Hostname
- 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 IPAddr's).
Examples:prep.ai.mit.eduwww.apache.org.
Note: 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 can take a remarkable deal of time when the connection to the name server uses a slow PPP link.
Note: 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 two hostsWWW.MyDomain.comandwww.mydomain.com.(note the trailing period) are considered equal.
See also
<Proxy> Directive
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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 *>
Order Deny,Allow
Deny from all
Allow from 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>
ProxyBlock Directive
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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. Example:
ProxyBlock joes-garage.com some-host.co.uk rocky.wotsamattau.edu
'rocky.wotsamattau.edu' would also be matched if referenced by IP address.
Note that 'wotsamattau' would also be sufficient to match 'wotsamattau.edu'.
Note also that
ProxyBlock *
blocks connections to all sites.
ProxyDomain Directive
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This directive is only useful for Apache 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.
Example
ProxyRemote * http://firewall.mycompany.com:81
NoProxy .mycompany.com 192.168.112.0/21
ProxyDomain .mycompany.com
ProxyErrorOverride Directive
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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).
ProxyIOBufferSize Directive
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<ProxyMatch> Directive
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The <ProxyMatch> directive is
identical to the <Proxy> directive, except it matches URLs
using regular expressions.
ProxyMaxForwards Directive
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The ProxyMaxForwards directive specifies the
maximum number of proxies through which a request may pass. This is
set to prevent infinite proxy loops, or a DoS attack.
Example
ProxyMaxForwards 10
ProxyPass Directive
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This directive allows remote servers to be mapped into the space of the local server; the local server does not act as a proxy in the conventional sense, but appears to be a mirror of the remote server. path is the name of a local virtual path; url is a partial URL for the remote server and cannot include a query string.
Suppose the local server has address http://wibble.org/;
then
ProxyPass /mirror/foo/ http://foo.com/
will cause a local request for the
<http://wibble.org/mirror/foo/bar> to be
internally converted into a proxy request to
<http://foo.com/bar>.
The ! directive is useful in situations where you don't want to reverse-proxy a subdirectory. eg.
ProxyPass /mirror/foo/i !
ProxyPass /mirror/foo http://foo.com
will proxy all requests to /mirror/foo to foo.com EXCEPT requests made to /mirror/foo/i
NB: order is important. you need to put the exclusions BEFORE the general proxypass directive
When used inside a <Location> section, the first argument is
ommitted and the local directory is obtained from the <Location>.
If you require a more flexible reverse-proxy configuration, see
the RewriteRule directive
with the [P] flag.
ProxyPassReverse Directive
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This directive lets Apache adjust the URL in the Location,
Content-Location and URI headers on
HTTP redirect responses. This is essential when Apache is used as
a reverse proxy to avoid by-passing the reverse proxy because of HTTP
redirects on the backend servers which stay behind the reverse proxy.
path is the name of a local virtual path.
url is a partial URL for the remote server - the same way they are
used for the ProxyPass directive.
Example:
Suppose the local server has address http://wibble.org/; then
ProxyPass /mirror/foo/ http://foo.com/
ProxyPassReverse /mirror/foo/ http://foo.com/
will not only cause a local request for the
<http://wibble.org/mirror/foo/bar> to be internally
converted into a proxy request to <http://foo.com/bar> (the
functionality ProxyPass provides here). It also takes care of
redirects the server foo.com sends: when http://foo.com/bar is
redirected by him to http://foo.com/quux Apache adjusts this to
http://wibble.org/mirror/foo/quux before forwarding the HTTP
redirect response to the client.
Note that this ProxyPassReverse directive can
also be used in conjunction with the proxy pass-through feature
("RewriteRule ... [P]") from
mod_rewrite because its doesn't depend on a
corresponding ProxyPass
directive.
When used inside a <Location> section, the first argument is
ommitted and the local directory is obtained from the <Location>.
ProxyPreserveHost Directive
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When enabled, this option will pass the Host: line from the incoming request to the proxied host, instead of the hostname specified in the proxypass line.
This option should normally be turned 'off'.
ProxyReceiveBufferSize Directive
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The ProxyReceiveBufferSize directive
specifies an explicit network buffer size for outgoing HTTP and FTP
connections, for increased throughput. It has to be greater than 512
or set to 0 to indicate that the system's default buffer size should
be used.
Example
ProxyReceiveBufferSize 2048
ProxyRemote Directive
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This defines remote proxies to this proxy. match is either the name of a URL-scheme that the remote server supports, or a partial URL for which the remote server should be used, or '*' to indicate the server should be contacted for all requests. remote-server is a partial URL for the remote server. Syntax:
remote-server = protocol://hostname[:port]
protocol is the protocol that should be used to communicate with the remote server; only "http" is supported by this module.
Example:
ProxyRemote http://goodguys.com/ http://mirrorguys.com:8000
ProxyRemote * http://cleversite.com
ProxyRemote ftp http://ftpproxy.mydomain.com:8080
In the last example, the proxy will forward FTP requests, encapsulated as yet another HTTP proxy request, to another proxy which can handle them.
This option also supports reverse proxy configuration - a backend webserver can be embedded within a virtualhost URL space even if that server is hidden by another forward proxy.
ProxyRemoteMatch Directive
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The ProxyRemoteMatch is identical
to the ProxyRemote
directive, except the first argument is a regular expression
match against the requested URL.
ProxyRequests Directive
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This allows or prevents Apache from functioning as a forward proxy
server. (Setting ProxyRequests to 'off' does not disable use of the
ProxyPass directive.)
In a typical reverse proxy configuration, this option should be set to 'off'.
Do not enable proxying with
ProxyRequestsuntil you have secured your server. Open proxy servers are dangerous both to your network and to the Internet at large.
ProxyTimeout Directive
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This directive allows a user to specifiy a timeout on proxy requests. This is usefull when you have a slow/buggy appserver which hangs, and you would rather just return a timeout and fail gracefully instead of waiting however long it takes the server to return
ProxyVia Directive
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This directive controls the use of the Via: HTTP
header by the proxy. Its intended use is to control the flow of of
proxy requests along a chain of proxy servers. See RFC2068 (HTTP/1.1)
for an explanation of Via: header lines.
- If set
to off, which is the default, no special processing is
performed. If a request or reply contains a
Via:header, it is passed through unchanged. - If set to on, each
request and reply will get a
Via:header line added for the current host. - If set to full, each generated
Via:header line will additionally have the Apache server version shown as aVia:comment field. - If set to block, every
proxy request will have all its
Via:header lines removed. No newVia:header will be generated.
