While cloning is never a real-time operation, synchronization can be. For system architectures that require high availability, or scalability, you will need some form of [[synchronization]] for various components of the system (disk, databases, etc.)
== Apt-get dpkg --set-selections ==
One way to do this on Debian-based systems (including Ubuntu) is to use <code>dpkg</code> get/set-selections in combination with <code>apt-get</code> using it's dselect-upgrade option: