Each instance (virtual machine) started from the same image is configured identically. The same account and the same procedure will be used to connect to it. If the machine image is public and if the instance is open to the Internet, which is common when using commercial providers such as Amazon, an attacker could connect randomly to known IPs from the cloud, and eventually access to an instance before its owner.
To individualise the connection to each instance, one can pass informations at startup, called instance metadata, which will be available to this instance only at a fixed HTTP URL. If the owner provides a public SSH key, this can be used to ensure that only the owner of the private key can connect.
After the next update of network-console, this method of connection will be available for the Debian Installer. Likewise for the Debian images produced, by installing the cloud-init packages, that I uploaded to the experimental section of our archive. This package is far from ready. It lacks init scripts, it is not translated, and to be honest, I have not tested it. But to have it in Debian makes me benefit from the package and bugs tracking systems. Do not hesitate to report some, or better, to participate to the maintenance of this package.
Cloud-init has many other interesting functionalities. I would like to thank Scott Moser, the upstream developer and maintainer of the Ubuntu package, for his cooperation during the creation of the Debian package, as I made large modifications, in particular the removal of the part managing the
menu.lst for pv-grub, which will have its own package or will be transferred somewhere else.