Filtering Ingresses by class

[cubic3d]

Currently it's impossible to filter which Ingress class should be taken into account for polling host names and Loadbalancer IPs.
Example: Two ingress-controllers nginx-int and nginx-ext each having an Ingress resource defining host.domain.tld - the resulting response to the query looks like that:

;; ANSWER SECTION:
host.domain.tld.	60	IN	A	192.168.99.2
host.domain.tld.	60	IN	A	192.168.99.1

But from the internal network (responsibility of the nginx-int controller) only one of those Loadbalancer IPs is accessible on the default port without IP restrictions which leads to timeouts and inability to access the service. Filtering based on ingressClassName and kubernetes.io/ingress.class or some sort of coredns.io/ignore annotation on resources is required to solve that.

[networkop]

yeah, it makes sense. The original CoreDNS issue had a suggestion for how this could be done. PRs are welcome

[cubic3d]

I still have an eye on this, just had no time yet ;)