Knative: Operator’s Handbook

Customizing external domain suffix

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

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

Configuring DNS records

If you want others to access {SERVICE}.{NAMESPACE}.yourdomain.com 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.