I am having a hard time finding the technical overview on the system/kernel upgrade process. Does Rancher use A/B partitions so that a failed boot can be detected and automatically reverted back to using the version prior to the upgrade attempt?
Some other wizardry?
RancherOS is really just a kernel and an initrd. The upgrade process is downloading a new kernel/initrd and updating the boot loader to point to it. We don’t remove the old kernel/initrd. If there is a problem you can select the old kernel from the bootloader (grub2 by default).
Upgrades are performed with the sudo ros os upgrade command.