kubernetes/cmd/kubeadm/app/phases/upgrade/policy.go

const MaximumAllowedMinorVersionUpgradeSkew …

const MaximumAllowedMinorVersionDowngradeSkew …

const MaximumAllowedMinorVersionKubeletSkew …

type VersionSkewPolicyErrors …

// EnforceVersionPolicies enforces that the proposed new version is compatible with all the different version skew policies
func EnforceVersionPolicies(versionGetter VersionGetter, newK8sVersionStr string, newK8sVersion *version.Version, allowExperimentalUpgrades, allowRCUpgrades bool) *VersionSkewPolicyErrors { … }

// detectUnstableVersionError is a helper function for detecting if the unstable version (if specified) is allowed to be used
func detectUnstableVersionError(newK8sVersion *version.Version, newK8sVersionStr string, allowExperimentalUpgrades, allowRCUpgrades bool) error { … }

// detectTooOldKubelets errors out if the kubelet versions are so old that an unsupported skew would happen if the cluster was upgraded
func detectTooOldKubelets(newK8sVersion *version.Version, kubeletVersions map[string][]string) error { … }