Change effective on 14 August 2018
Internal Routing routing is a new feature for apps in Private Spaces. Internally routed apps work exactly the same as other Heroku apps (custom domain, SSL termination, logging), except their web processes are exposed as endpoints that are only routable within the Private Space network and from VPC-peered and VPN-connected networks. Internally routed apps are not accessible from the public internet.
Create internally routed apps with the Heroku CLI:
$ heroku apps:create --internal-routing --space test-space Creating app... done, ⬢ frozen-oasis-70544 http://frozen-oasis-70544.herokuapp.com/ | https://git.heroku.com/frozen-oasis-70544.git
See the Internal Routing Dev Center article for details on how to create and use internally routed apps.