Unfortunately we deprecated this sample application as it was focused on migrating applications around maintenance windows.
Now that we have live migration and transparent maintenance windows, developers no longer need to move components of their application around zones due to impeding maintenance. Additionally, Cloud SQL now supports MySQL wire protocol which significantly reduces the complexities of managing applications for high availability.
In the future we may develop a new application, but it will be greatly simplified since we can offload load balancing to Compute Engine load balancer and persistency to Cloud Datastore and Cloud SQL.