Proxy Directives: IBM HTTP Server
System Administration IBM HTTP Server documentation

Proxy Directives


AllowCONNECT

  • Compatibility - AllowCONNECT is only available in Apache 1.3.2 and above.
  • Context - Server configuration, virtual host
  • Default - AllowCONNECT 443 563
  • Module - mod_proxy
  • Status - Base
  • Syntax - AllowCONNECT <port list>

The AllowCONNECT directive specifies a list of port numbers to which the proxy CONNECT method may connect. Browsers use this method when an 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 only to the listed ports.

CacheDefaultExpire

  • Compatibility - CacheDefaultExpire is only available in Apache 1.1 and above.
  • Context - Server configuration, virtual host
  • Default - CacheDefaultExpire 1
  • Module - Mod_proxy
  • Status - Base
  • Syntax - CacheDefaultExpire <time>

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

CacheDirLength

  • Compatibility - CacheDirLength is only available in Apache 1.1 and above.
  • Context - Server configuration, virtual host
  • Default - CacheDirLength 1
  • Module - mod_proxy
  • Status - Base
  • Syntax - CacheDirLength <length>

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

CacheDirLevels

  • Compatibility - CacheDirLevels is only available in Apache 1.1 and above.
  • Context - Server config, virtual host
  • Default - CacheDirLevels 3
  • Module - mod_proxy
  • Status - Base
  • Syntax - CacheDirLevels <levels>

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

CacheForceCompletion

  • Compatibility - CacheForceCompletion is only available in Apache 1.3.1 and above.
  • Context - Server configuration, virtual host
  • Default - 90
  • Module - mod_proxy
  • Status - Base
  • Syntax - CacheForceCompletion <percentage>

If an HTTP transfer being cached is canceled, the proxy module completes 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.

ProxyRequests

  • Syntax - ProxyRequests on | off
  • Default - ProxyRequests Off
  • Context - Server configuration, virtual host
  • Status - Base
  • Module - mod_proxy
  • Compatibility - ProxyRequests is only available in Apache 1.1 and later.

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

ProxyRemote

  • Default - None
  • Syntax - ProxyRemote <match> <remote-server>
  • Context - Server configuration, virtual host
  • Status - Base
  • Module - mod_proxy
  • Compatibility - ProxyRemote is only available in Apache 1.1 and later.

This directive 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]

Use the protocol, <protocol> 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 another HTTP proxy request, to a separate proxy, which can handle them.

ProxyPass

  • Syntax - ProxyPass <path> <url> <path> <url>
  • Context -Server configuration, virtual host
  • Status - Base
  • Module - mod_proxy
  • Compatibility - ProxyPass is only available in Apache 1.1 and later.

This directive allows remote servers to map into the space of the local server; the local server does not act as a proxy in the conventional sense, but appears as 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>.

ProxyPassReverse

  • Syntax - ProxyPassReverse <path> <url> <path> <url>
  • Context - Server configuration, virtual host
  • 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. This capability is essential when Apache is used as a reverse proxy, to avoid by-passing the reverse proxy because of HTTP redirects on the back end 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.

ProxyBlock

  • Syntax - ProxyBlock <word/host/domain list>
  • Context - Server configuration, virtual host
  • 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.

ProxyReceiveBufferSize

  • Syntax - ProxyReceiveBufferSize <bytes>
  • Context - Server config, virtual host
  • 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 default buffer size should be used.

Example:

  ProxyReceiveBufferSize 2048

NoProxy

  • Syntax - NoProxy NoProxy { <Domain> | <SubNet> | <IpAddr> | <Hostname> }
  • Context - Server configuration, virtual host
  • 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

ProxyDomain

  • Syntax - ProxyDomain <Domain>
  • Context - Server configuration, virtual host
  • 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 to which the apache proxy server will belong. 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

  • Syntax -ProxyVia {off|on|full|block}
  • Default - ProxyVia off
  • Context - Server configuration, virtual host
  • 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.

CacheRoot

  • Syntax - CacheRoot <directory>
  • Context - Server config, virtual host
  • 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 caching; without defining a CacheRoot, proxy functionality will be available if ProxyRequests are set to On, but no caching will be available.

CacheSize

  • CacheSize <size>
  • Default - CacheSize 5
  • Context - Server configuration, virtual host
  • 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.

CacheGcInterval

  • Syntax - CacheGcInterval <time>
  • Context - Server config, virtual host
  • Status - Base
  • Module - mod_proxy
  • Compatibility - CacheGcInterval is only available in Apache 1.1 and later

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

  • Syntax - CacheMaxExpire <time>
  • Default - CacheMaxExpire 24
  • Context - Server configuration, virtual host
  • Status - Base
  • Module - mod_proxy
  • Compatibility - CacheMaxExpire is only available in Apache 1.1 and later.

Cacheable 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

  • Syntax - CacheLastModifiedFactor <factor>
  • Default - CacheLastModifiedFactor 0.1
  • Context - Server configuration, virtual host
  • 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.

NoCache

  • Syntax - CacheDefaultExpire <time>
  • Default - CacheDefaultExpire 1
  • Context - Server configuration, virtual host
  • Status - Base
  • Module - mod_proxy
  • Compatibility - CacheDefaultExpire 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.