"Demo the application " is broken

[bsdnet]

https://github.com/mvallim/kubernetes-under-the-hood/blob/master/documentation/kube-demo-application.md#creating-the-guestbook-frontend-deployment

The container gbfrontend:v4/v5 does not exist. Looks v4 or v5 tag was removed from Google Container Registry and the application was broken.

The source code is: https://github.com/kubernetes/examples/blob/master/guestbook/frontend-deployment.yaml#L19

The better way is using private registry and set contained.