systemd v254 added soft-reboot, a reboot type that keeps the same kernel running, but restarts the whole of userspace into a new rootfs, while serializing state across (e.g.: File Descriptor Store). In v255 the ability for select system services/portable services/containers to survive the reboot uninterrupted was added. On an image-based Linux system this allows atomically updating the rootfs without causing interruptions for workloads that run on discrete and separate filesystem images. This talk will briefly explore this new feature, listing new improvements from the latest version, and showing a demo of a soft-reboot being applied on an Azure Boost machine with two surviving critical portable services running without interruptions while the rest of the OS is restarted.

We will explore what container runtimes maintainers would need to do in order to support this feature. systemd-portabled already supports it for Portable Services.