httpd: mod_cache only caching your homepage
Published January 25th, 2010
modcache has a pretty inflexible configuration setup. [CacheEnable](http://httpd.apache.org/docs/2.2/mod/modcache.html#cacheenable) can only take a prefix of a path to be cached, and to disable a sub-path with CacheDisable, you need to list all of the possible prefixes (ie, no regular expressions).
Lets say you want to cache just your root page, aka ’/’, for your website, just in case you get hit by a Slashdot Effect.
For Apache httpd 2.2.12 or newer, you can do this by first enabling Caching on All pages, then setting the no-cache enviroment variable globally, and then unsetting it for a specific path:
CacheDirLevels 2 CacheDirLength 1 CacheEnable disk / CacheRoot /var/cache/apache2/mod_disk_cache CacheIgnoreHeaders Set-Cookie CacheIgnoreNoLastMod On CacheMaxExpire 600 SetEnv no-cache <LocationMatch "^/$"> UnsetEnv no-cache </LocationMatch>
For Apache httpd before 2.2.12, you need a different method of disabling caching globally, and then re-enabling it. The easiest way is using mod_headers, to muck with Vary header
Header set Vary * <LocationMatch "^/$"> Header unset Vary </LocationMatch>
Strictly speaking, doing this to the Vary header is an RFC violation, and you best bet is to upgrade to a newer httpd version. :-)
This works because mod_cache will refuse to cache any HTTP resource with a Vary value of ”
*”, because this is saying that every response form the origin will be different.
Written by Paul Querna, CTO @ ScaleFT. @pquerna