Kairos upgrades are atomic in the sense that the new version of the OS fully replaces the old one or it doesn’t replace it at all. This allows users to test the upgrade in the lab, before they upgrade any of their nodes and be sure that the upgrade will work the same way in production. While this is very useful strategy, failed upgrades cannot be completely avoided. Some difference in hardware, a network hick-up or even a human error, can result in a failed upgrade.
