Apache模块 mod_cache

概述

This module should be used with care and can be used to circumvent Allow和Deny directives. You should not enable caching for any content to which you wish to limit access by client host name, address or environment variable.

mod_cache implements an RFC 2616 compliant HTTP content cache that can be used to cache either local or proxied content. mod_cache requires the services of one or more storage management modules. Two storage management modules are included in the base Apache distribution:

mod_disk_cache

implements a disk based storage manager.

mod_mem_cache

implements a memory based storage manager. mod_mem_cache can be configured to operate in two modes: caching open file descriptors or caching objects in heap storage. mod_mem_cache can be used to cache locally generated content or to cache backend server content for mod_proxy when configured using ProxyPass (aka <dfn class="calibre27">reverse proxy</dfn>)

Content is stored in and retrieved from the cache using URI based keys. Content with access protection is not cached.

Related Modules and Directives

相关模块

• mod_disk_cache

• mod_mem_cache

  相关指令

• CacheRoot

• CacheSize
• CacheDirLevels
• CacheDirLength
• CacheMinFileSize
• CacheMaxFileSize
• MCacheSize
• MCacheMaxObjectCount
• MCacheMinObjectSize
• MCacheMaxObjectSize
• MCacheRemovalAlgorithm
• MCacheMaxStreamingBuffer

Sample Configuration

Sample httpd.conf

      #

      # Sample Cache Configuration

      #

      LoadModule cache_module modules/mod_cache.so

      <IfModule mod_cache.c>

 #LoadModule disk_cache_module modules/mod_disk_cache.so

        # If you want to use mod_disk_cache instead of mod_mem_cache,

        # uncomment the line above and comment out the LoadModule line below.

        <IfModule mod_disk_cache.c>

 CacheRoot c:/cacheroot

          CacheEnable disk  /

          CacheDirLevels 5

          CacheDirLength 3
        </IfModule>

        LoadModule mem_cache_module modules/mod_mem_cache.so

        <IfModule mod_mem_cache.c>

 CacheEnable mem  /

          MCacheSize 4096

          MCacheMaxObjectCount 100

          MCacheMinObjectSize 1

          MCacheMaxObjectSize 2048
        </IfModule>

        # When acting as a proxy, don't cache the list of security updates

        CacheDisable http://security.update.server/update-list/
      </IfModule>

CacheDefaultExpire 指令

CacheDefaultExpire directive specifies a default time, in seconds, to cache a document if neither an expiry date nor last-modified date are provided with the document. The value specified with the CacheMaxExpire directive does not override this setting.

      CacheDefaultExpire 86400

CacheDisable 指令

CacheDisable directive instructs mod_cache to not cache urls at or below url-string.

示例

      CacheDisable /local_files

CacheEnable 指令

CacheEnable directive instructs mod_cache to cache urls at or below url-string. The cache storage manager is specified with the cache_type argument. cache_type mem instructs mod_cache to use the memory based storage manager implemented by mod_mem_cache. cache_type disk instructs mod_cache to use the disk based storage manager implemented by mod_disk_cache. cache_type fd instructs mod_cache to use the file descriptor cache implemented by mod_mem_cache.

In the event that the URL space overlaps between different CacheEnable directives (as in the example below), each possible storage manager will be run until the first one that actually processes the request. The order in which the storage managers are run is determined by the order of the CacheEnable directives in the configuration file.

      CacheEnable  mem   /manual

      CacheEnable  fd    /images

      CacheEnable  disk  /

When acting as a forward proxy server, url-string can also be used to specify remote sites and proxy protocols which caching should be enabled for.

      # Cache proxied url's

      CacheEnable  disk  /

      # Cache FTP-proxied url's

      CacheEnable  disk  ftp://

      # Cache content from www.apache.org

      CacheEnable  disk  http://www.apache.org/

CacheIgnoreCacheControl 指令

Ordinarily, requests containing a Cache-Control: no-cache or Pragma: no-cache header value will not be served from the cache. The CacheIgnoreCacheControl directive allows this behavior to be overridden. CacheIgnoreCacheControl On tells the server to attempt to serve the resource from the cache even if the request contains no-cache header values. Resources requiring authorization will never be cached.

      CacheIgnoreCacheControl On

Warning:

This directive will allow serving from the cache even if the client has requested that the document not be served from the cache. This might result in stale content being served.

参见

• CacheStorePrivate
• CacheStoreNoStore

CacheIgnoreHeaders 指令

According to RFC 2616, hop-by-hop HTTP headers are not stored in the cache. The following HTTP headers are hop-by-hop headers and thus do not get stored in the cache in any case regardless of the setting of CacheIgnoreHeaders:

• Connection
• Keep-Alive
• Proxy-Authenticate
• Proxy-Authorization
• TE
• Trailers
• Transfer-Encoding
• Upgrade

CacheIgnoreHeaders specifies additional HTTP headers that should not to be stored in the cache. For example, it makes sense in some cases to prevent cookies from being stored in the cache.

CacheIgnoreHeaders takes a space separated list of HTTP headers that should not be stored in the cache. If only hop-by-hop headers not should be stored in the cache (the RFC 2616 compliant behaviour), CacheIgnoreHeaders can be set to None.

Example 1

      CacheIgnoreHeaders Set-Cookie

Example 2

      CacheIgnoreHeaders None

Warning:

If headers like Expires which are needed for proper cache management are not stored due to a CacheIgnoreHeaders setting, the behaviour of mod_cache is undefined.

CacheIgnoreNoLastMod 指令

Ordinarily, documents without a last-modified date are not cached. Under some circumstances the last-modified date is removed (during mod_include processing for example) or not provided at all. The CacheIgnoreNoLastMod directive provides a way to specify that documents without last-modified dates should be considered for caching, even without a last-modified date. If neither a last-modified date nor an expiry date are provided with the document then the value specified by the CacheDefaultExpire directive will be used to generate an expiration date.

      CacheIgnoreNoLastMod On

CacheLastModifiedFactor 指令

In the event that a document does not provide an expiry date but does provide a last-modified date, an expiry date can be calculated based on the time since the document was last modified. The CacheLastModifiedFactor directive specifies a factor to be used in the generation of this expiry date according to the following formula: expiry-period = time-since-last-modified-date * factor expiry-date = current-date + expiry-period 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 current time was 3:00pm then the computed expiry-date would be 3:00pm + 1hour = 4:00pm. If the expiry-period would be longer than that set by CacheMaxExpire, then the latter takes precedence.

      CacheLastModifiedFactor 0.5

CacheMaxExpire 指令

CacheMaxExpire directive specifies the maximum number of seconds 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 seconds. This maximum value is enforced even if an expiry date was supplied with the document.

      CacheMaxExpire 604800

CacheStoreNoStore 指令

Ordinarily, requests or responses with Cache-Control: no-store header values will not be stored in the cache. The CacheStoreNoCache directive allows this behavior to be overridden. CacheStoreNoCache On tells the server to attempt to cache the resource even if it contains no-store header values. Resources requiring authorization will never be cached.

      CacheStoreNoStore On

Warning:

As described in RFC 2616, the no-store directive is intended to "prevent the inadvertent release or retention of sensitive information (for example, on backup tapes)." Enabling this option could store sensitive information in the cache. You are hereby warned.

参见

• CacheIgnoreCacheControl
• CacheStorePrivate

CacheStorePrivate 指令

Ordinarily, responses with Cache-Control: private header values will not be stored in the cache. The CacheStorePrivate directive allows this behavior to be overridden. CacheStorePrivate On tells the server to attempt to cache the resource even if it contains private header values. Resources requiring authorization will never be cached.

      CacheStorePrivate On

Warning:

This directive will allow caching even if the upstream server has requested that the resource not be cached. This directive is only ideal for a 'private' cache.

参见

• CacheIgnoreCacheControl
• CacheStoreNoStore