Apache mod_proxy_html Substitute: how to re-use part of regex match? (regex variables?)

SetEnvIf's Request_URI parameter seems to be updated with the path of the error document when it's in the process of serving one.

One workaround would be to match against something else that would have the parent path present, such as the Referer header.

What I normally do is first enable mod_proxy and mod_proxy_ajp. Depending on your distribution you a2enmod mod_proxy_ajp and it enables them both as ajp depends on mod_proxy.

Then I add something like this:

<IfModule mod_proxy_ajp.c>
  <Location /tomcat-context>
     ProxyPass ajp://IP-or-FQDN/tomcat-context
     ProxyReversePass ajp://IP-or-FQDN/tomcat-context
  </Location>
</IfModule>

This part is placed inside my <VirtualHost>. The rest is basic configuration set by the OS (just like your configuration shows, with ProxyRequests Off etc.)

UPDATE: What you need to change, or at least verify is your tomcat server.xml. It must have the ajp-container enabled like this:

<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

You can disable the connector on 8080 if that is all you serve from tomcat and if you do not need the backend. In case you don't have access to this, or ports for ajp are disabled, you can basically achieve the same wirth 8080. Just replace the ajp:// tag in the provided configuration with http:// and add :8080 after IP-or-FQDN.

UPDATE 2 To serve / just write

<IfModule mod_proxy_ajp.c>
  <Location />
    ProxyPass ajp://IP-or-FQDN/tomcat-context
    ProxyReversePass ajp://IP-or-FQDN/tomcat-context
  </Location>
</IfModule>

Ensure you comment out the DocumentRoot /path/to/old/documentroot/ directive and the <Directory /path/to/old/documentroot/> in your apache configuration.