Images with cloud content were configured by the distribution manufacturer to work under the hypervisor, such as OpenStack, EC2, kvm and LXC (not strictly a hypervisor), and not on physical equipment. This entails removing packages that are only needed in physical environments, such as wireless drivers, etc., and adding packages that are useful in the cloud. For example, during the download process, cloud files download metadata from the environment, such as host name and network information. This data is used to “personalize” the new instance when it is loaded for the first time.
If you really want to find nuts and bolts, the Ubuntu UEC Images Page contains many details about the composition of Ubuntu cloud images and other information, such as how to build it yourself.
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