This sample is running on: https://java-grails3.is-easy-on-scalingo.com/

First, you need to have a working grails environment: http://docs.grails.org/latest/guide/gettingStarted.html#requirements

Then, simply execute:

grails run-app

Create an application on https://scalingo.com, then:

scalingo -a my-app git-setup
git push scalingo master

And that's it!