config/v1/types_cluster_operator: Expand upgradeable inputs to cluster scope#926
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openshift-merge-robot merged 1 commit intoJun 14, 2021
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…r scope Consider these cases: a. Component A is in a state that allows updates, and nothing in the rest of the cluster would break if A updated. b. Component A is in a state that allows updates, but component B (which is in-cluster, but not part of A) would break if A updated. c. Component A would break if it updated. Operator A should pretty clearly be Upgradeable=True for (a) and Upgradeable=False for (c). Before this commit, a narrow reading of the comment would have operator A be Upgradeable=True for (b). This commit moves it to Upgradeable=False, based on discussion in [1], where it becomes the job of the API-server to set Upgradeable=False if updating the API-server would break nodes running old kubelets. The API-server can say "to unblock minor updates, update your kubelets". The machine-config operator will simultaneously say "hey, your kubelets are old, and here's how to update: $STEPS", but it won't use Upgradeable=False to say that (because the machine-config operator would be _happy_ to have its component nodes updated). As pointed out in discussion in [1], this is a bit of a bottomless pit. For example, component A may be removing a deprecated feature on update, and there may be user workloads that occasionally depend on that feature but hardly ever use it. Component A might reasonably think "nobody has used $OUTGOING_FEATURE in the last week, so I'm Upgradeable=True", and then post-update, the user-workload would go to hit the removed API and break. And obviously in-cluster components will have even more limited access to any out-of-cluster components that depend on them. So using Upgradeable=False to protect other components from breaking is going to be a best-effort sort of thing. But this commit pivots so that it's more clear that we'll put that effort in when we can. [1]: openshift/enhancements#762
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I'm fuzzy on this comment about the API-server being a client of the kubelet for exec flows. Perhaps that is sufficient to get the kubelet-skew-guard in under (c)? And maybe we want the godocs to be generic enough that operator B could say "hey, A is going to fast, wait for me to catch up" would be possible for cases where A isn't smart enough to notice B falling behind? Wording would be something like:
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Consider these cases:
a. Component A is in a state that allows updates, and nothing in the rest of the cluster would break if A updated.
b. Component A is in a state that allows updates, but component B (which is in-cluster, but not part of A) would break if A updated.
c. Component A would break if it updated.
Operator A should pretty clearly be
Upgradeable=Truefor (a) andUpgradeable=Falsefor (c).Before this commit, a narrow reading of the comment would have operator A be
Upgradeable=Truefor (b). This commit moves it toUpgradeable=False, based on discussion in openshift/enhancements#762, where it becomes the job of the API-server to setUpgradeable=Falseif updating the API-server would break nodes running old kubelets. The API-server can say "to unblock minor updates, update your kubelets". The machine-config operator will simultaneously say "hey, your kubelets are old, and here's how to update:$STEPS", but it won't useUpgradeable=Falseto say that (because the machine-config operator would be happy to have its component nodes updated).As pointed out in discussion in openshift/enhancements#762, this is a bit of a bottomless pit. For example, component A may be removing a deprecated feature on update, and there may be user workloads that occasionally depend on that feature but hardly ever use it. Component A might reasonably think "nobody has used
$OUTGOING_FEATUREin the last week, so I'mUpgradeable=True", and then post-update, the user-workload would go to hit the removed API and break. And obviously in-cluster components will have even more limited access to any out-of-cluster components that depend on them. So usingUpgradeable=Falseto protect other components from breaking is going to be a best-effort sort of thing. But this commit pivots so that it's more clear that we'll put that effort in when we can.