Adam Drew explains how to address this in this comment on the CDN re-route ticket for containerized/stage:

The second issue you are facing is that the /preview/apps/openshift route isn't being created. You have 2 options to solve this:

1. Change the name of your frontend resource to openshift - all of the networking resources are generated from the frontend resource name automatically, so if you change it to openshift you'll get the right routes. This would allow you to remove the route path in your frontend resource
2. Add an additional route path in your frontend resource for /preview/apps/openshift

I recommend option 1 because it will ensure you get everything for free.