Likely error you’ll see immediately is due to a change in GCP way of behaving.

ERROR: (gcloud.compute.images.create) Could not fetch resource:
— The resource ‘https://www.googleapis.com/storage/v1/b/zentralopensource/o/zentral-all-in-one.tar.gz' of type ‘Google Cloud Storage object’ was not found.

The zentral-all-in-one.tar.g artifact is indeed public world readable — however our friend Torbjorn has covered the steps to succeed here:

https://medium.com/@Torbjorn_59818/working-around-ec68e565e284