https://docs.redhat.com/en/documentation/red_hat_openstack_platform/17.1/html/configuring_dns_as_a_service/intro-dns-service_rhosp-dnsaas#dns-service-common-deploy-scenario_intro-dns-service

I think we may be missing the most common scenario our customers would be looking to use Designate for: A non-public facing DNS for internal DNS resolution of their resources.
At least I've been already a couple of cases where customers would want to deploy zones like cloud.example.internal.
Our examples all rely on how top level domain resolution would search for a .com or .org TLD.

Here you have 2 case examples of such requests: 03806176 and 03951623