mod_disk_cache - directive CacheRoot ignored in context "server config" but not inside a virtual host

Oliver Feiler <oliver.feiler@xxxxxxxxxxxxx> · Wed, 11 Nov 2009 10:20:31 +0100

Hi,

I have an issue with Apache's mod_disk_cache and the config directive CacheRoot. The versions used are as follows. It's a default Debian 5 Apache with mpm-worker used as a reverse proxy.

# apache2ctl -V
Server version: Apache/2.2.9 (Debian)
Server built:   Jul 14 2009 20:40:18
Server's Module Magic Number: 20051115:15
Server loaded:  APR 1.2.12, APR-Util 1.2.12
Compiled using: APR 1.2.12, APR-Util 1.2.12
Architecture:   64-bit
Server MPM:     Worker
  threaded:     yes (fixed thread count)
    forked:     yes (variable process count)

The CacheRoot is defined via an include (Debian's default config layout) and mapped into the main config.

CacheRoot /var/cache/apache2/mod_disk_cache

My guess (as per documentation) is that this defines the default CacheRoot to be used by all configured proxy virtual hosts. If I now define a virtual host like the following:

<VirtualHost something:80>
  [...]
  ProxyVia On
  ProxyPreserveHost On
  ProxyPass / balancer://something/
  <Proxy balancer://something/>
    BalancerMember http://backend1
    BalancerMember http://backend2
  </Proxy>
  CacheMaxFileSize 8000000
  CacheEnable disk /
</VirtualHost>

The proxy now works as expected, but nothing will be cached in the disk cache. There are no age headers generated by the proxy on served requests. Now if I add the directive
CacheRoot /var/cache/apache2/mod_disk_cache
to this virtual host, the disk cache fills and age headers are sent as expected.

I feel like I'm missing something or made a really stupid mistake with the config. It works if I repeat the CacheRoot statement for all virtual hosts, but I'd rather define it globally since there are quite a number of virtual hosts.

Thanks and kind regards,

Oliver Feiler

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