Knative: Operator’s Handbook

Customizing external domain suffix

As described in default domains, Knative by default uses as the suffix to register services to the external load balancer.

However, you don't own :) Follow this guide to change the suffix.

Configuring DNS records

If you want others to access {SERVICE}.{NAMESPACE} and go to your app, you need to configure DNS records on your domain's nameservers so that they point to Knative’s external ingress gateway.

Neither of the options will hide your services from the public internet, you should make your service internal (cluster-local) for that.