Add warnings back in

cmd/minikube/cmd/start.go

@@ -1204,6 +1204,50 @@ func getKubernetesVersion(old *config.MachineConfig) string {
 		exit.WithCodeT(exit.Data, `Unable to parse "{{.kubernetes_version}}": {{.error}}`, out.V{"kubernetes_version": paramVersion, "error": err})
 	}
 	nv := version.VersionPrefix + nvs.String()
+
+	if old == nil || old.KubernetesConfig.KubernetesVersion == "" {
+		return nv
+	}
+
+	oldestVersion, err := semver.Make(strings.TrimPrefix(constants.OldestKubernetesVersion, version.VersionPrefix))
+	if err != nil {
+		exit.WithCodeT(exit.Data, "Unable to parse oldest Kubernetes version from constants: {{.error}}", out.V{"error": err})
+	}
+	defaultVersion, err := semver.Make(strings.TrimPrefix(constants.DefaultKubernetesVersion, version.VersionPrefix))
+	if err != nil {
+		exit.WithCodeT(exit.Data, "Unable to parse default Kubernetes version from constants: {{.error}}", out.V{"error": err})
+	}
+
+	if nvs.LT(oldestVersion) {
+		out.WarningT("Specified Kubernetes version {{.specified}} is less than the oldest supported version: {{.oldest}}", out.V{"specified": nvs, "oldest": constants.OldestKubernetesVersion})
+		if viper.GetBool(force) {
+			out.WarningT("Kubernetes {{.version}} is not supported by this release of minikube", out.V{"version": nvs})
+		} else {
+			exit.WithCodeT(exit.Data, "Sorry, Kubernetes {{.version}} is not supported by this release of minikube", out.V{"version": nvs})
+		}
+	}
+
+	ovs, err := semver.Make(strings.TrimPrefix(old.KubernetesConfig.KubernetesVersion, version.VersionPrefix))
+	if err != nil {
+		glog.Errorf("Error parsing old version %q: %v", old.KubernetesConfig.KubernetesVersion, err)
+	}
+
+	if nvs.LT(ovs) {
+		nv = version.VersionPrefix + ovs.String()
+		profileArg := ""
+		if old.Name != constants.DefaultMachineName {
+			profileArg = fmt.Sprintf("-p %s", old.Name)
+		}
+		exit.WithCodeT(exit.Config, `Error: You have selected Kubernetes v{{.new}}, but the existing cluster for your profile is running Kubernetes v{{.old}}. Non-destructive downgrades are not supported, but you can proceed by performing one of the following options:
+
+* Recreate the cluster using Kubernetes v{{.new}}: Run "minikube delete {{.profile}}", then "minikube start {{.profile}} --kubernetes-version={{.new}}"
+* Create a second cluster with Kubernetes v{{.new}}: Run "minikube start -p <new name> --kubernetes-version={{.new}}"
+* Reuse the existing cluster with Kubernetes v{{.old}} or newer: Run "minikube start {{.profile}} --kubernetes-version={{.old}}"`, out.V{"new": nvs, "old": ovs, "profile": profileArg})
+
+	}
+	if defaultVersion.GT(nvs) {
+		out.T(out.ThumbsUp, "Kubernetes {{.new}} is now available. If you would like to upgrade, specify: --kubernetes-version={{.new}}", out.V{"new": defaultVersion})
+	}
 	return nv
 }