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 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

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

Common configuration topics

• 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?
• 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 all
Allow from yournetwork.example.com
</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.

For more information, see mod_access.

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?

How can I access FTP files outside of my home directory?

A 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 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@

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.

ProxyRequests directive

This allows or prevents Apache from functioning as a 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.

ProxyRemote directive

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 directive

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 directive

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 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.

AllowCONNECT directive

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.

ProxyBlock directive

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

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

Note also that

ProxyBlock *

ProxyReceiveBufferSize directive

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

ProxyIOBufferSize directive

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

NoProxy directive

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 directive

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

ProxyVia directive

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.

CacheForceCompletion directive

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.

CacheRoot directive

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.

CacheSize directive

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.

CacheGcInterval directive

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.

CacheMaxExpire directive

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.

CacheLastModifiedFactor directive

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 directive

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

CacheDirLength directive

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

CacheDefaultExpire directive

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.

NoCache directive

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 *

Apache HTTP Server Version 1.3