Comment by cjbprime | Hacker News Reader

Comment by cjbprime | Hacker News Reader

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> This ran in CI and would fail the build if it didn't pass.

I don't mean to be pedantic, but since we're talking about what should happen instead, this is insufficient. It works until the day you realize you made some kind of manual change to your CI infra, or that CI has some non-standard configuration that makes it work for you but not some significant fraction of the fleet.

People should do what you described in CI, but as well as that, you need phased rollout, where e.g. the build can only be rolled out to the next percentage point of randomly selected users in a specific segment (e.g. each hardware revision and country as independent segments) after meeting a ratio of successful check-ins, in the field, from the new build by production customers in that segment. That's the actual metric for proceeding with the rollout: actual customers are successfully checking in from the new version of the software.

Except, that's actually not sufficient either. What if the new build is good, but it contains an update to the updater which bricks the updater? Now you're getting successful check-ins from the new version in the field, but none of those customers will ever successfully auto-update again. So, test the new updater's ability to go forwards successfully, too.

A good way to handle the who-updates-the-updater issue is to use a triple partition updater. A updates B, and then B updates C, then C updates A. If anything about the new version prevents it from properly updating its neighbor, that neighbor won't be able to close the loop, and you'll fall back to A. This simplifies the FSBL, because it just boots the three partitions in a loop, no failure detection required. You don't need to triplicate the full application either, just the minimum system needed to perform an update, and then have the "application" in it's own partition to be called by the updater.

> It works until the day you realize you made some kind of manual change to your CI infra, or that CI has some non-standard configuration that makes it work for you but not some significant fraction of the fleet.

Nah, my CI process was solid. This was proven in the field over the course of years.

> I don't mean to be pedantic... you need phased rollout

You don't need to be pedantic, but better to ask the question rather than assume that was all that I did. =) You have to realize that what I built, worked flawlessly. It wasn't easy either, took a lot of trial and error.

I did have a CIDR based rollout. I could specify down to the individual box that it would run a specific version. Or I could write "latest" to always keep certain boxes running on the latest build. This was another part of my testing, but ended up not being fully necessary because I had enough automated testing in CI that "latest" always worked.

> but it contains an update to the updater which bricks the updater?

This happened, so I wrote a lot of test code to make sure that would never happen again. My CI would catch that since I was E2E testing that it could actually run the upgrade process.

Once I implemented all of this, I never had a single failure and would routinely, several times a day, deploy to the entire cluster, over the course of a couple years.

It was all eventually consistent as I could also control the "check for update" frequency as well.

I think there's a minor confusion here, where you think the purpose of my response involves doubting whether your system was successful. I understand it was successful. My response is to the sense in which your comment can be interpreted as advice to other people on what they should build.

I think the fact that you were able to survive with CI-only doesn't mean that we should encourage others to skip implementing a phased rollout based on verified customer successes, including testing of their new updaters before the first time they accidentally brick all the updaters, rather than afterwards. That's what I was hoping to help avoid, through my comment.

And you need to verify the vehicle is not in motion.

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