[mvip]

+1 for "full immutable system image update"

People who suggest updating individual packages (or even worse, individual deb packages for instance) have never deployed any large scale IoT/Embedded projects. These devices are very different than servers/desktops and will break in ways you can't imagine. We started out using deb packages at Screenly before moving to Ubuntu Core, and the amount of error/recovery logic we had written to recover from broken deb package state was insane at that point.