docs: Add note to 1.22 about the CA CN rename

[agilgur5]

Summary

Add a note in 1.22 changelog about #11921 et al's CA changes

Details

• this broke some of my teams' automation code that relied on the CN, so thought it would be good to call out in case anyone else stumbles upon this in order to not spend a few hours debugging 😅
  • this change may particularly impact Prod environments, where the cluster has not been rebuilt in some time (years), and so they will have the old CN while new clusters in lower environments will have the new CN
    • so code that relies on the CN may unexpectedly break Production while working fine in lower environments 😬 😬 😬
      • fortunately we caught this in our QA env, but it passed Dev fine

Testing Evidence

From an internal fix my team made to another team's automation:

(We've recommend they pull the CA from /etc/kubernetes/pki/ca.crt or /var/run/secrets/kubernetes.io/serviceaccount/ca.crt to be a bit more resilient to changes like this)

Review Notes

Feel free to change the language / wording as you see fit or put in a different part of the release notes (I put this under "Other changes of note" right now).

I thought specifically warning about older clusters was important, as otherwise this is particularly easy to overlook

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[agilgur5]

@johngmyers any chance you could take a look at this PR?

[johngmyers]

I must admit to being at a loss as to why anything would depend on the CN having a particular value.

[agilgur5]

The automation I mentioned here was for the Vault k8s integration, which requires the k8s CA.

Can see in the screenshot above that this code does TLS inspection to pull the CA, but ends up getting two certs, the CA and the kubernetes-master cert. It uses the CN to distinguish between the two.

I don't think that's the best way to get the CA, as I mentioned in the opening, but regardless, a team I work with already had code that specifically depended on the CN. I.e. the CN was part of the "public surface" that kOps exposes, and changing the CN broke existing code. Whether or not that code is optimal or why that code exists, the fact that any code exists anywhere that relies on the CN is enough to show this.

As is oft stated in Linux kernel development, anything that is exposed will be used (aka the "Workflow" xkcd).

So at the very least, I think this should be documented in the changelog, which is all that this PR does.
Per the opening, I think it is doubly important to document since this has a higher likelihood to break code that depends on the CN in Prod, as those clusters are often older / rebuilt less often and so may still have the old CN. Per opening, code that worked in Dev may actually fail in Prod as a result, with potentially very significant consequences (in the case here, several Vault integrations would fail, eventually resulting in downtime).

[agilgur5]

@johngmyers can you take a look again?

[johngmyers]

I don't think this rises to the level of a release note. This is an implementation detail; the CN of a root CA is not something that is supposed to matter to anything.

[agilgur5]

I don't think this rises to the level of a release note.

It's a breaking change that broke actual code in production exactly because it wasn't mentioned in the release notes...

A reasonable user could suggest much more than a tiny release note when a change broke prod. This is the bare minimum, in my opinion.

the CN of a root CA is not something that is supposed to matter to anything.

It did. This is not a hypothetical...
Only one counter-example is needed to show that.

[johngmyers]

kOps 1.22 has been out of support for about a year. One person making an incorrect assumption about internals does not merit a release note.

[agilgur5]

kOps 1.22 has been out of support for about a year.

I'll repeat once more that this breaking change affects clusters that upgraded to 1.22 and beyond and were not rebuilt in that time. Which is, again, much more likely for Prod clusters that have zero downtime (i.e. high criticality).
This affects all clusters that existed pre-1.22 and were upgraded to 1.22+ through the standard kOps upgrade process.

A cluster that was upgraded from 1.21 to 1.26, which is current, would also have this issue. As written above, that cluster, which would be on 1.26, would have the old CN, while clusters built with 1.22+, and similarly on 1.26, would have the newer CN. Two clusters on 1.26 could have two different CNs, despite having the same configuration.

The CA has a different CN depending on what version of kOps the cluster was originally created with (not the version it's on).

One person making an incorrect assumption about internals

I'm not the one who made that assumption (and it was in fact, code reviewed by a whole team that has used kOps for years), and I, myself, literally said there are better ways of implementing their code.
But I also would not have been able to definitively tell them not to rely on that. That is, similarly, undocumented behavior.

It is also a CA, they are not really meant to change frequently either. Whether a CA should be considered an "internal" is debatable.

[agilgur5]

One person making an incorrect assumption about internals

the CN of a root CA is not something that is supposed to matter to anything.

One could say that this too, is an assumption. And there is an existing counter-example that shows it did, in fact, matter to something... So one could further say that that is "an incorrect assumption" 🤷

I'm not here to play word games and state opinions, I am stating facts about events that literally already happened.
I am here to warn other users about that, because if we did not catch that in QA, that would have resulted in a major issue to a large enterprise company. I would not wish production outages upon anybody, nor hours of debugging and root cause analysis (which required reading through kOps source code and individual commit diffs), and the absolute least I can do is add a tiny warning to the release notes.

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/remove-lifecycle stale

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[agilgur5]

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[hakman]

/lgtm
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[hakman]

/ok-to-test

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