By default, images used are based on Ubuntu’s daily cloud images.
The image search is filtered based on a variety of options, which vary from cloud to cloud. Here is an example for Amazon’s EC2:
filters = [ 'arch=%s' % arch, 'endpoint=%s' % 'https://ec2.%s.amazonaws.com' % self.region, 'region=%s' % self.region, 'release=%s' % release, 'root_store=%s' % root_store, 'virt=hvm', ]
This allows for the root store to be configurable by the user.