I am trying to migrate my app from Openshift 2 FREE to Openshift 3 FREE. I've managed to do everything, but the custom domain. In OpenShift it was very easy - add an alias to the app + modify some CNAME records in your domain. Now I do not find it easy.
Could anyone elaborate?
OpenShift Online Starter does not support you being able to use a custom domain. Only OpenShift Online Pro support customs domains at this point in time.
The only way to have a custom domain with OpenShift Online Starter, is to use Cloudflare or other service which can act as a proxy in front and which accepts requests for your custom domain name and forwards on requests onto OpenShift at the generated hostname given you.