In OpenShift, choose a downloaded cartridge, with the following URL : http://cartreflect-claytondev.rhcloud.com/reflect?github=akovacs/openshift-cartridge-scala
On git push, sbt compile will be called, then the script start.sh at the root of your repo will be called.
Example of start.sh script:
#!/bin/bash
sbt run com.example.Boot.main
Make sure start.sh is an executable file: chmod +x start.sh
In your application listen on the environment variable $OPENSHIFT_SCALA_IP:$OPENSHIFT_SCALA_PORT
interface = System.getenv("OPENSHIFT_SCALA_IP")
port = System.getenv("OPENSHIFT_SCALA_PORT").toInt
This cartidge embed a spray example, but you could use any framework as long as sbt is used for compilation.