In ARO, a number of entries are added to /etc/hosts to handle internal hostname resolution for private networks. This is sufficient for services running directly on the host, but for pods to be able to make use of these entries they need to also be served by a DNS server listed in /etc/resolv.conf.

The CoreDNS instance used for the Custom DNS feature is just such a DNS server. Custom DNS will always be enabled in ARO once the feature is available because it is also needed for api/api-int/*.apps resolution.

Enabling the CoreDNS hosts plugin in the configuration file for this instance of CoreDNS should be sufficient to expose the existing entries added by ARO to pods. The host's /etc/hosts file will need to be bind-mounted into the static CoreDNS pod.

It should be safe to add this unconditionally, as generally there is nothing in /etc/hosts that should not be exposed to pods.