Explanation
Scenario: Ensure that webapp2.azurewebsites.net can be accessed by using the name app2.contoso.com When you create a Cloud Service, Azure assigns it to a subdomain of cloudapp.net. For example, if your Cloud Service is named "contoso", your users will be able to access your application on a URL like http:// contoso.cloudapp.net. Azure also assigns a virtual IP address.
However, you can also expose your application on your own domain name, such as contoso.com.
References:
https://docs.microsoft.com/en-us/azure/cloud-services/cloud-services-custom-domain-name-portal