Ubuntu's 'Daily Build' images aren't for us
In response to my wish for easily updating the packages on Ubuntu ISO images, Aneurin Price brought up jigdo. In researching what Jigdo is, I wound up running into a tantalizing mention of Ubuntu daily builds (perhaps from here). This sent me off to Internet searches and eventually I wound up on Ubuntu's page for the Ubuntu Server 16.04.2 LTS (Xenial Xerus) Daily Build. This looked like exactly what we wanted, already pre-built for us (which is perfectly fine by me, I'm happy to have someone else do the work of putting in all of the latest package updates for us).
However, when I went looking around Ubuntu's site I couldn't find any real mention of these daily builds, including such things as what they were for, how long they got updated, and so on. That made me a bit nervous, so I pulled down the latest 'current' 16.04 server build and took a look inside the ISO image. Unfortunately I must report that it turns out to not be suitable for what we want, ironically because it has packages that are too fresh. Well, a package; all I looked at was the kernel image. At the moment, the current daily ISO has a kernel package that is marked as being '4.4.0-85', while the latest officially announced and released Ubuntu kernel is 4.4.0-83. We may like having current updates in our install ISOs, but we draw the line at future updates that are still presumably in testing and haven't been officially released (and may never be, if some problem is found or they're replaced by even newer ones).
To be clear, I'm not blaming Ubuntu. They do daily builds for not-yet-released Ubuntu versions, which are obviously 'don't use these on anything you care about', so there is no particular reason why the daily builds for released Ubuntu versions would be any different (and there are perfectly good reasons for wanting the very latest test packages in a bundle). I was just hopeful when I found this site, so now I'm reporting a negative result.
PS: I'm just guessing as to why this image has kernel 4.4.0-85. As mentioned, I haven't found much information from Ubuntu on what these daily builds are about (for already-released versions), and I don't know too much about how potential updates flow through Ubuntu's work processes and so on. I did find this page on their kernel workflow and its link to this report page, and also this bug that's tracking 4.4.0-85 and its changelog.