OpenNebula uses the notions of "Images" and "Templates". From what I've been able to understand so far, an image is first downloaded from the marketplace, then a template is created from it, and finally a virtual machine is created from the template.
This seems a bit superfluous to me. Why have both images and templates? What's the difference? Why not a two-step process like: get an image (or template?) and then create a VM from it?
Best Answer
Having Templates and Images allows you to use the same image in different VMs. For example, if the image is non-persistent you can launch a VM with 4GB of memory and another one with 16GB without the need to duplicate the source image in your storage.