4.6. Custom Domains and SSL Certificates

In order to use your own DNS entries instead of using the domain generated for you by the system, OpenShift Online enables you to designate custom domain aliases for applications. For the alias to work correctly, ensure that you have a CNAME record with your DNS provider.
For added security, you can use custom SSL certificates with domain aliases. Note that custom SSL certificates are only available to users with upgraded OpenShift Online accounts.
Management Console
You can manage custom domain names and SSL certificates in the management console. Click on an application name in the My Applications tab to view custom domain name and SSL certificate management options for the selected application.

4.6.1. Adding a custom domain name

Domain name aliases can be added to applications using the rhc alias add AppName Alias command: 
$ rhc alias add racer fast.cars.com

RESULT:
Alias 'fast.cars.com' has been added.