symfony appCache PURGE在负载均衡器后面

I've got a little problem invalidating my appCache in symfony behind a loadbalancer.

When I create the PURGE request (done with curl) I have to use the internal port the webserver listens to. This one is different than the external port 80 or 443 exposed to the public by the loadbalancer. But the invalidate() method uses the complete request including the port to generate the cacheKey - so I can't internally invalidate the cache build by requests from users outside!

I have tried to use X_FORWARDED_FOR and other headers in my purge-request but had no success.

Is there a way to achieve this by not messing inside the AppCache.php and replace the port in the request manually?

Thank you very much!