The following images are now obsolete:
If you want to deploy a Ruby application to Google App Engine, you can simply specify "runtime: ruby" in your app.yaml configuration file.
If you'd like to extend the Ruby runtime for App Engine, use "gcr.io/google-appengine/ruby" as the base image.
See http://cloud.google.com/ruby for more information on using Ruby on Google Cloud Platform.
If you are looking for a generic Ruby base image, consider the official Ruby image on DockerHub.