Comment 10 for bug 1475568

There's a lot of discussion on IRC going on about this, but I feel like this feature is currently too underspecified for us to tackle it. Here are some questions:

When are "OTA numbers" assigned? Is it before or after the image is published? Before or after the image is copied to stable?

Who assigns OTA numbers?

Which images will have an OTA #?

Will an OTA # ever be assigned or changed after an image is published?

Is it only required to know the OTA # that a device is currently on, or so you want to know the OTA # for a target upgrade? E.g. "The device is on OTA 5 but an upgrade will leave you on OTA 7"?

I think it should be a hard requirement that there are no additional downloads from sites other than system-image.ubuntu.com. There should also be no new required download machinery than what's already there, because of the battle-hardened nature of the existing code.

If a system-image client change is required, can we use this as the driving factor for finally adopting system-image 3 on the phone? Or will this have to be backported to 2.5.x? We've wanted to get everything on 3.0 for a long while now and it doesn't make sense absent security requirements to continue the 2.5.x series.