I've created a new GCE instance and took a snapshot of it's persistnet boot disk. Now I would like to create a template based on this snapshot, to allow horizontal scaling, but I don't see the snapshot during the image selection when creating a new instance.
How can I create a new instance from an existing snapshot ?
Snapshots are just an instant representation of a persistent disk only. It does not save the google configurations of the instance using it. Nothing forbid you to take a snapshot of an unattached disk for example. Moreover, a snapshot is not bootable, it means that you have to create an image from it.
In order to create an instance group, you have to create an image from you snapshot you've taken and you have to create an instance template base on that newly created image.