Fix `kubeadm upgrade plan` for offline operation

cmd/kubeadm/app/phases/upgrade/compute.go

@@ -62,7 +62,7 @@ type ClusterState struct {
 // GetAvailableUpgrades fetches all versions from the specified VersionGetter and computes which
 // kinds of upgrades can be performed
 func GetAvailableUpgrades(versionGetterImpl VersionGetter, experimentalUpgradesAllowed, rcUpgradesAllowed bool) ([]Upgrade, error) {
-	fmt.Println("[upgrade] Fetching available versions to upgrade to:")
+	fmt.Println("[upgrade] Fetching available versions to upgrade to")
 
 	// Collect the upgrades kubeadm can do in this list
 	upgrades := []Upgrade{}
@@ -82,7 +82,9 @@ func GetAvailableUpgrades(versionGetterImpl VersionGetter, experimentalUpgradesA
 	// Get and output the current latest stable version
 	stableVersionStr, stableVersion, err := versionGetterImpl.VersionFromCILabel("stable", "stable version")
 	if err != nil {
-		return nil, err
+		fmt.Printf("[upgrade/versions] WARNING: %v\n", err)
+		fmt.Println("[upgrade/versions] WARNING: Falling back to current kubeadm version as latest stable version")
+		stableVersionStr, stableVersion = kubeadmVersionStr, kubeadmVersion
 	}
 
 	// Get the kubelet versions in the cluster
@@ -115,9 +117,8 @@ func GetAvailableUpgrades(versionGetterImpl VersionGetter, experimentalUpgradesA
 		// Get and output the latest patch version for the cluster branch
 		patchVersionStr, patchVersion, err := versionGetterImpl.VersionFromCILabel(versionLabel, description)
 		if err != nil {
-			return nil, err
-		}
-
+			fmt.Printf("[upgrade/versions] WARNING: %v\n", err)
+		} else {
 			// Check if a minor version upgrade is possible when a patch release exists
 			// It's only possible if the latest patch version is higher than the current patch version
 			// If that's the case, they must be on different branches => a newer minor version can be upgraded to
@@ -145,6 +146,7 @@ func GetAvailableUpgrades(versionGetterImpl VersionGetter, experimentalUpgradesA
 				})
 			}
 		}
+	}
 
 	if canDoMinorUpgrade {
 		upgrades = append(upgrades, Upgrade{

cmd/kubeadm/app/phases/upgrade/versiongetter.go

@@ -86,7 +86,7 @@ func (g *KubeVersionGetter) KubeadmVersion() (string, *versionutil.Version, erro
 func (g *KubeVersionGetter) VersionFromCILabel(ciVersionLabel, description string) (string, *versionutil.Version, error) {
 	versionStr, err := kubeadmutil.KubernetesReleaseVersion(ciVersionLabel)
 	if err != nil {
-		return "", nil, fmt.Errorf("Couldn't fetch latest %s version from the internet: %v", description, err)
+		return "", nil, fmt.Errorf("Couldn't fetch latest %s from the internet: %v", description, err)
 	}
 
 	if description != "" {
@@ -95,7 +95,7 @@ func (g *KubeVersionGetter) VersionFromCILabel(ciVersionLabel, description strin
 
 	ver, err := versionutil.ParseSemantic(versionStr)
 	if err != nil {
-		return "", nil, fmt.Errorf("Couldn't parse latest %s version: %v", description, err)
+		return "", nil, fmt.Errorf("Couldn't parse latest %s: %v", description, err)
 	}
 	return versionStr, ver, nil
 }