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Upgrades and Version Skew

Upgrading Kubernetes isn't a single sweep — it follows an order, because components are allowed to skew versions within strict limits: kubelet may be up to three minors older than the apiserver but never newer. This article inspects the cluster's version skew, explains why the apiserver must be upgraded first, then drills the hardest part of upgrading a node: cordon, drain, uncordon — on the real worker-0, fully reversible.