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Apache HTTP Server Version 1.3
Apache module mod_proxy
This module provides for an HTTP 1.1 caching proxy server.
Status:
Extension
Source
File: mod_proxy.c
Module
Identifier: proxy_module
Compatibility:
Available in Apache 1.1 and later.
Summary
This module implements a proxy/cache for Apache. It implements proxying capability for FTP,
CONNECT (for SSL), HTTP/0.9, HTTP/1.0, and (as of
Apache 1.3.23) 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. As of Apache 1.2, mod_proxy stability is greatly
improved.
Warning: 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.
Directives
Syntax:
ProxyRequests on|off
Default:
ProxyRequests Off
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyRequests is only available in Apache 1.1 and later.
This allows or prevents Apache from functioning as a forward proxy server. Setting
ProxyRequests to 'off' does not disable use of the
ProxyPass
directive.
Warning: Do not enable proxying until you have
secured
your server. Open proxy servers are dangerous both to your network and to the Internet at
large.
Syntax:
ProxyRemote match remote-server
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyRemote is only available in Apache 1.1 and later.
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.
Syntax:
ProxyPass path url
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyPass is only available in Apache 1.1 and later.
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.
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>.
Warning: The
ProxyRequests
directive should usually be set off when using ProxyPass.
Syntax:
ProxyPassReverse path url
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyPassReverse is only available in Apache 1.3b6 and later.
This directive lets Apache adjust the URL in the Location header on HTTP redirect
responses. For instance 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.
Syntax:
AllowCONNECT port [port] ...
Default:
AllowCONNECT 443 563
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
AllowCONNECT is only available in Apache 1.3.2 and later.
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 override this default and allow connections to
the listed ports only.
Syntax:
ProxyBlock *|word|host|domain [word|host|domain] ...
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyBlock is only available in Apache 1.2 and later.
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.
Syntax:
ProxyReceiveBufferSize bytes
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyReceiveBufferSize is only available in Apache 1.3 and later.
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
Syntax:
ProxyIOBufferSize bytes
Default:
8192
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyIOBufferSize is only available in Apache 1.3.24 and later.
The ProxyIOBufferSize directive specifies the number of bytes that will be read from a
remote HTTP or FTP server at one time. This directive is different from the
ProxyReceiveBufferSize directive, which specifies the low level socket buffer size.
When a response is received which fits entirely within the IO buffer size, the remote HTTP
or FTP server socket will be closed before an attempt is made to write the response to the
client. This ensures that the remote server does not remain connected unnecessarily while the
response is delivered to a slow client. A high value for the IO buffer decreases the load on
remote HTTP and FTP servers, at the expense of greater RAM footprint on the proxy.
Example:
ProxyIOBufferSize 131072
Syntax:
NoProxy Domain|SubNet|IpAddr|Hostname [Domain|SubNet|IpAddr|Hostname] ...
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
NoProxy is only available in Apache 1.3 and later.
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.com
and .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:
- 192.168 or 192.168.0.0
- 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 192.168.112.0/21 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.
- 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.
See Also:
DNS
Issues
- 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.edu www.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 hosts WWW.MyDomain.com
and www.mydomain.com. (note the trailing period) are considered equal.
See Also:
DNS
Issues
Syntax:
ProxyDomain Domain
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyDomain is only available in Apache 1.3 and later.
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
Syntax:
ProxyVia on|off|full|block
Default:
ProxyVia off
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
ProxyVia is only available in Apache 1.3.2 and later.
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 a Via: comment field.
- If set to block, every proxy request will have all its Via: header
lines removed. No new Via: header will be generated.
Syntax:
CacheForceCompletion percentage
Default:
90
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheForceCompletion is only available in Apache 1.3.1 and later.
If an http transfer that is being cached is cancelled, the proxy module will complete the
transfer to cache if more than the percentage specified has already been transferred.
This is a percentage, and must be a number between 1 and 100, or 0 to use the default. 100
will cause a document to be cached only if the transfer was allowed to complete. A number
between 60 and 90 is recommended.
Syntax:
CacheRoot directory
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheRoot is only available in Apache 1.1 and later.
Sets the name of the directory to contain cache files; this must be writable by the httpd
server. (see the User
directive).
Setting CacheRoot enables proxy cacheing; without defining a CacheRoot,
proxy functionality will be available if ProxyRequests are set to On,
but no cacheing will be available.
Syntax:
CacheSize kilobytes
Default:
CacheSize 5
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheSize is only available in Apache 1.1 and later.
Sets the desired space usage of the cache, in KB (1024-byte units). Although usage may grow
above this setting, the garbage collection will delete files until the usage is at or below
this setting.
Depending on the expected proxy traffic volume and CacheGcInterval, use a value
which is at least 20 to 40 % lower than the available space.
Syntax:
CacheGcInterval hours
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheGcinterval is only available in Apache 1.1 and later.
Check the cache after the specified number of hours, and delete files if the space
usage is greater than that set by CacheSize. Note that hours accepts a float value,
you could for example use CacheGcInterval 1.5 to check the cache every 90
minutes. (If unset, no garbage collection will be performed, and the cache will grow
indefinitely.) Note also that the larger the CacheGcInterval, the more extra
space beyond the configured CacheSize will be needed for the cache between
garbage collections.
Syntax:
CacheMaxExpire hours
Default:
CacheMaxExpire 24
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheMaxExpire is only available in Apache 1.1 and later.
Specifies the maximum number of hours for which cachable HTTP documents will be
retained without checking the origin server. Thus, documents will be out of date at most this
number of hours This restriction is enforced even if an expiry date was supplied with
the document.
Syntax:
CacheLastModifiedFactor factor
Default:
CacheLastModifiedFactor 0.1
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheLastModifiedFactor is only available in Apache 1.1 and later.
If the origin HTTP server did not supply an expiry date for the document, then estimate one
using the formula
expiry-period = time-since-last-modification * factor
For example, if the document was last modified 10 hours ago, and factor is 0.1, then
the expiry period will be set to 10*0.1 = 1 hour.
If the expiry-period would be longer than that set by CacheMaxExpire, then the latter takes
precedence.
Syntax:
CacheDirLevels levels
Default:
CacheDirLevels 3
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheDirLevels is only available in Apache 1.1 and later.
CacheDirLevels sets the number of levels of subdirectories in the cache. Cached
data will be saved this many directory levels below CacheRoot.
Syntax:
CacheDirLength length
Default:
CacheDirLength 1
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheDirLength is only available in Apache 1.1 and later.
CacheDirLength sets the number of characters in proxy cache subdirectory names.
Syntax:
CacheDefaultExpire hours
Default:
CacheDefaultExpire 1
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
CacheDefaultExpire is only available in Apache 1.1 and later.
If the document is fetched via a protocol that does not support expiry times, then use the
specified number of hours as the expiry time.
CacheMaxExpire
does not override this setting.
Syntax:
NoCache *|word|host|domain [word|host|domain] ...
Default:
None
Context:
server config, virtual host
Override:
Not applicable
Status:
Base
Module:
mod_proxy
Compatibility:
NoCache is only available in Apache 1.1 and later.
The NoCache directive specifies a list of words, hosts and/or domains, separated by spaces.
HTTP and non-passworded FTP documents from matched words, hosts or domains are not
cached 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:
NoCache joes-garage.com some-host.co.uk bullwinkle.wotsamattau.edu
'bullwinkle.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
NoCache *
disables caching completely.
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