It's not possible to invalidate cache when using our Docker stack, because Symfony's TRUSTED_PROXIES are set incorrectly.

In https://github.com/ezsystems/ezplatform/blob/master/doc/docker/varnish.yml#L12 we set the value varnish, but Symfony does not resolve hostnames - Symfony expects an IP there, so it doesn't work and varnish container is not treated as a trusted proxy by Symfony.

Initial issue: https://github.com/ezsystems/docker-php/pull/34