Apache HTTP Server Version 1.3

Apache module mod_proxy

Note:

This module was experimental in Apache 1.1.x. As of Apache 1.2, mod_proxy stability is greatly improved.

Summary

Directives

• ProxyRequests
• ProxyRemote
• ProxyPass
• ProxyPassReverse
• ProxyBlock
• ProxyReceiveBufferSize
• NoProxy
• ProxyDomain
• CacheRoot
• CacheSize
• CacheMaxExpire
• CacheDefaultExpire
• CacheLastModifiedFactor
• CacheGcInterval
• CacheDirLevels
• CacheDirLength
• NoCache

ProxyRequests

This allows or prevents Apache from functioning as a proxy server. Setting ProxyRequests to 'off' does not disable use of the ProxyPass directive.

ProxyRemote

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]

Example:

  ProxyRemote http://goodguys.com/ http://mirrorguys.com:8000
  ProxyRemote * http://cleversite.com
  ProxyRemote ftp http://ftpproxy.mydomain.com:8080

ProxyPass

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

ProxyPassReverse

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

Note that this ProxyPassReverse directive can also by used in conjunction with the proxy pass-through feature ("RewriteRule ... [P]") from mod_rewrite because its doesn't depend on a corresponding ProxyPass directive.

ProxyBlock

The ProxyBlock directive specifies a list of words, hosts and/or domains, separated by spaces. HTTP, HTTPS, and FTP document requests to 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

Note that 'wotsamattau' would also be sufficient to match 'wotsamattau.edu'.

Note also that

ProxyBlock *

ProxyReceiveBufferSize

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

NoProxy

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 

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

ProxyDomain

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

CacheRoot

Sets the name of the directory to contain cache files; this must be writable by the httpd server.

CacheSize

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.

CacheGcInterval

Check the cache every <time> hours, and delete files if the space usage is greater than that set by CacheSize.

CacheMaxExpire

Cachable HTTP documents will be retained for at most <time> hours without checking the origin server. Thus documents can be at most <time> hours out of date. This restriction is enforced even if an expiry date was supplied with the document.

CacheLastModifiedFactor

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>

If the expiry-period would be longer than that set by CacheMaxExpire, then the latter takes precedence.

CacheDirLevels

CacheDirLevels sets the number of levels of subdirectories in the cache. Cached data will be saved this many directory levels below CacheRoot.

CacheDirLength

CacheDirLength sets the number of characters in proxy cache subdirectory names.

CacheDefaultExpire

If the document is fetched via a protocol that does not support expiry times, then use <time> hours as the expiry time. CacheMaxExpire does not override this setting.

NoCache

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

Note that 'wotsamattau' would also be sufficient to match 'wotsamattau.edu'.

Note also that

NoCache *

Common configuration topics

• Controlling access to your proxy
• Using Netscape hostname shortcuts
• Why doesn't file type xxx download via FTP?
• Why does Apache start more slowly when using the proxy module?
• Can I use the Apache proxy module with my SOCKS proxy?
• What other functions are useful for an intranet proxy server?

Controlling access to your proxy

<Directory proxy:*>
order deny,allow
deny from [machines you'd like *not* to allow by IP address or name]
allow from [machines you'd like to allow by IP address or name]
</Directory>

A <Files> block will also work, and is the only method known to work for all possible URLs in Apache versions earlier than 1.2b10.

Using Netscape hostname shortcuts

Why doesn't file type xxx download via FTP?

application/octet-stream        bin dms lha lzh exe class tgz taz

How can I force an FTP ASCII download of File xxx?

Why does Apache start more slowly when using the proxy module?

Can I use the Apache proxy module with my SOCKS proxy?

Some users have reported problems when using SOCKS version 4.2 on Solaris. The problem was solved by upgrading to SOCKS 4.3.

Remember that you'll also have to grant access to your Apache proxy machine by permitting connections on the appropriate ports in your SOCKS daemon's configuration.

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.

Apache HTTP Server Version 1.3

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