The post is about backup management for AlloyDB. It might be useful for the time when it is written but, probably, will be obsolete very soon when tools and API for the service will mature.
A couple of words about AlloyDB backups and how they are created. The backups are quite different from the default backups for Cloud SQL for example. As we know in Cloud SQL all the backups are bound to the instance. What it means is when the instance is deleted then all the backups disappear along with the instance. It makes sense if the backups behind the scenes are storage snapshots from the databases. But in AlloyDB all the backups are decoupled from the cluster and exist by themselves. If you delete a cluster the backups stay. I think it is a way better approach because it provides a better way to protect from some mistakes when an instance is deleted before making a clone or exporting the data. As for now you can see all the backups for existing and deleted instances using the “backups” tab in the console, gcloud utility or listing using GCP REST API.