Comment by sam_bristow

I've had a reasonable amount of luck with a combination of Buildroot and Bazel. I use Buildroot to assemble a minimal Base OS with just the kernel, bootloader and a few system services. Then the application layer is built with Bazel and assembled into a set of squashfs images which are mounted as overlay filesystems at boot time. The whole thing is shipped as a SWUpdate file built with the Bazel layer.

Because most of the iteration is happening in the Bazel layers I can generate a full system update in about 15 seconds with everything being fully reproducible.