Add additional version check

pkg/upgrader/upgrade/preflight_checks.go

@@ -63,6 +63,13 @@ func runPreflightChecks(ctx *util.Context) error {
 	if err := verifyVersion(ctx, nodes, ctx.Verbose); err != nil {
 		return fmt.Errorf("unable to verify components version: %v", err)
 	}
+	if err := verifyVersionSkew(ctx, nodes, ctx.Verbose); err != nil {
+		if ctx.ForceUpgrade {
+			ctx.Logger.Warningf("version skew check failed: %v", err)
+		} else {
+			return fmt.Errorf("version skew check failed: %v", err)
+		}
+	}
 
 	return nil
 }
@@ -147,13 +154,43 @@ func verifyEndpoints(nodes *corev1.NodeList, hosts []*config.HostConfig, verbose
 	return nil
 }
 
-// verifyVersion ensures it's possible to upgrade to the requested version and that the version skew policy is fulfilled
+// verifyVersion verifies is it possible to upgrade to the requested version
 func verifyVersion(ctx *util.Context, nodes *corev1.NodeList, verbose bool) error {
 	reqVer, err := semver.NewVersion(ctx.Cluster.Versions.Kubernetes)
 	if err != nil {
 		return fmt.Errorf("provided version is invalid: %v", err)
 	}
 
+	var highestKubelet *semver.Version
+	for _, n := range nodes.Items {
+		kubelet, err := semver.NewVersion(n.Status.NodeInfo.KubeletVersion)
+		if err != nil {
+			return err
+		}
+		if highestKubelet == nil || highestKubelet.Compare(kubelet) < 0 {
+			highestKubelet = kubelet
+		}
+	}
+
+	if reqVer.Equal(highestKubelet) {
+		return fmt.Errorf("requested version is same as current")
+	}
+	// Check are we upgrading to newer minor or patch release
+	if reqVer.Minor()-highestKubelet.Minor() < 0 ||
+		(reqVer.Minor() == highestKubelet.Minor() && reqVer.Patch() < highestKubelet.Patch()) {
+		return fmt.Errorf("requested version can't be lower than current")
+	}
+
+	return nil
+}
+
+// verifyVersionSkew ensures the requested version matches the version skew policy
+func verifyVersionSkew(ctx *util.Context, nodes *corev1.NodeList, verbose bool) error {
+	reqVer, err := semver.NewVersion(ctx.Cluster.Versions.Kubernetes)
+	if err != nil {
+		return fmt.Errorf("provided version is invalid: %v", err)
+	}
+
 	// Check API server version
 	var apiserverVersion *semver.Version
 	apiserverPods, err := ctx.Clientset.CoreV1().Pods(metav1.NamespaceSystem).List(metav1.ListOptions{
@@ -220,7 +257,7 @@ func checkVersionSkew(reqVer, currVer *semver.Version, diff int64) error {
 	}
 	// Check are we upgrading to newer minor or patch release
 	if reqVer.Minor()-currVer.Minor() < 0 ||
-		(reqVer.Minor() == currVer.Minor() && reqVer.Patch() < reqVer.Patch()) {
+		(reqVer.Minor() == currVer.Minor() && reqVer.Patch() < currVer.Patch()) {
 		return fmt.Errorf("requested version can't be lower than current")
 	}
 	// Ensure the version skew policy

pkg/upgrader/upgrade/preflight_checks_test.go

@@ -205,29 +205,35 @@ func TestCheckVersionSkewInvalid(t *testing.T) {
 			diff:           2,
 		},
 		{
-			name:           "upgrade 1.13.0 to 1.12.1 with diff of 1",
+			name:           "downgrade 1.13.0 to 1.12.1 with diff of 1",
 			currentVersion: semver.MustParse("1.13.0"),
 			desiredVersion: semver.MustParse("1.12.1"),
 			diff:           1,
 		},
 		{
-			name:           "upgrade 1.13.3 to 1.12.1 with diff of 1",
+			name:           "downgrade 1.13.3 to 1.12.1 with diff of 1",
 			currentVersion: semver.MustParse("1.13.3"),
 			desiredVersion: semver.MustParse("1.12.1"),
 			diff:           1,
 		},
 		{
-			name:           "upgrade 1.13.3 to 1.12.3 with diff of 1",
+			name:           "downgrade 1.13.3 to 1.12.3 with diff of 1",
 			currentVersion: semver.MustParse("1.13.3"),
 			desiredVersion: semver.MustParse("1.12.3"),
 			diff:           1,
 		},
 		{
-			name:           "upgrade 1.13.3 to 1.12.4 with diff of 1",
+			name:           "downgrade 1.13.3 to 1.12.4 with diff of 1",
 			currentVersion: semver.MustParse("1.13.3"),
 			desiredVersion: semver.MustParse("1.12.4"),
 			diff:           1,
 		},
+		{
+			name:           "downgrade 1.13.3 to 1.13.2 with diff of 1",
+			currentVersion: semver.MustParse("v1.13.3"),
+			desiredVersion: semver.MustParse("v1.13.2"),
+			diff:           1,
+		},
 	}
 	for _, tc := range testcases {
 		tc := tc