[yocto] Yocto-ish upgrade-in-place strategy

[Patrick Doyle]

Rather than inventing this from scratch yet again, I would like to ask
what the Yocto-ish best practice is for deploying an embedded system
that has to support in-place upgrades.

It seems to me that this should be a fairly common scenario:
I have (or, rather am in the process of developing yet another) an
embedded application that will be running on a device whose power
supply is uncertain at best.  Consequently, I want to run from a
read-only squashfs rootfs, with some small amount of seldom changed
configuration data (most likely stored in a JFFS partition).

But I need a strategy to upgrade this system in place.  Since I am
running from a read-only squashfs, I can't apt-get or rpm upgrade
individual packages.  I must redeploy the entire image.

I can divvy up the flash however I want, so I am thinking that I would
like to use u-boot to boot a rescue image from one partition, that
would kexec the deployed image from a different parition.

Are there Yocto recipes, blogs, community experience with this sort of
thing, or should I invent my own solution?

Again, this feel like a common problem that others should have already
solved, and I would rather solve uncommon problems than re-solve
common ones.

--wpd