cleanup: kubeadm upgrade plan supports json/yaml output

Co-authored-by: Lubomir I. Ivanov <neolit123@gmail.com>

cmd/kubeadm/app/apis/output/types.go

@@ -78,7 +78,7 @@ type ComponentConfigVersionState struct {
 type UpgradePlan struct {
 	metav1.TypeMeta
 
-	Components []*ComponentUpgradePlan
+	Components []ComponentUpgradePlan
 
 	ConfigVersions []ComponentConfigVersionState
 }

cmd/kubeadm/app/apis/output/v1alpha2/types.go

@@ -78,7 +78,7 @@ type ComponentConfigVersionState struct {
 type UpgradePlan struct {
 	metav1.TypeMeta
 
-	Components []*ComponentUpgradePlan `json:"components"`
+	Components []ComponentUpgradePlan `json:"components"`
 
 	ConfigVersions []ComponentConfigVersionState `json:"configVersions"`
 }

cmd/kubeadm/app/apis/output/v1alpha2/zz_generated.conversion.go

@@ -180,7 +180,7 @@ func Convert_output_Images_To_v1alpha2_Images(in *output.Images, out *Images, s
 }
 
 func autoConvert_v1alpha2_UpgradePlan_To_output_UpgradePlan(in *UpgradePlan, out *output.UpgradePlan, s conversion.Scope) error {
-	out.Components = *(*[]*output.ComponentUpgradePlan)(unsafe.Pointer(&in.Components))
+	out.Components = *(*[]output.ComponentUpgradePlan)(unsafe.Pointer(&in.Components))
 	out.ConfigVersions = *(*[]output.ComponentConfigVersionState)(unsafe.Pointer(&in.ConfigVersions))
 	return nil
 }
@@ -191,7 +191,7 @@ func Convert_v1alpha2_UpgradePlan_To_output_UpgradePlan(in *UpgradePlan, out *ou
 }
 
 func autoConvert_output_UpgradePlan_To_v1alpha2_UpgradePlan(in *output.UpgradePlan, out *UpgradePlan, s conversion.Scope) error {
-	out.Components = *(*[]*ComponentUpgradePlan)(unsafe.Pointer(&in.Components))
+	out.Components = *(*[]ComponentUpgradePlan)(unsafe.Pointer(&in.Components))
 	out.ConfigVersions = *(*[]ComponentConfigVersionState)(unsafe.Pointer(&in.ConfigVersions))
 	return nil
 }

cmd/kubeadm/app/apis/output/v1alpha2/zz_generated.deepcopy.go

@@ -128,14 +128,8 @@ func (in *UpgradePlan) DeepCopyInto(out *UpgradePlan) {
 	out.TypeMeta = in.TypeMeta
 	if in.Components != nil {
 		in, out := &in.Components, &out.Components
-		*out = make([]*ComponentUpgradePlan, len(*in))
+		*out = make([]ComponentUpgradePlan, len(*in))
-		for i := range *in {
+		copy(*out, *in)
-			if (*in)[i] != nil {
-				in, out := &(*in)[i], &(*out)[i]
-				*out = new(ComponentUpgradePlan)
-				**out = **in
-			}
-		}
 	}
 	if in.ConfigVersions != nil {
 		in, out := &in.ConfigVersions, &out.ConfigVersions

cmd/kubeadm/app/apis/output/zz_generated.deepcopy.go

@@ -128,14 +128,8 @@ func (in *UpgradePlan) DeepCopyInto(out *UpgradePlan) {
 	out.TypeMeta = in.TypeMeta
 	if in.Components != nil {
 		in, out := &in.Components, &out.Components
-		*out = make([]*ComponentUpgradePlan, len(*in))
+		*out = make([]ComponentUpgradePlan, len(*in))
-		for i := range *in {
+		copy(*out, *in)
-			if (*in)[i] != nil {
-				in, out := &(*in)[i], &(*out)[i]
-				*out = new(ComponentUpgradePlan)
-				**out = **in
-			}
-		}
 	}
 	if in.ConfigVersions != nil {
 		in, out := &in.ConfigVersions, &out.ConfigVersions

cmd/kubeadm/app/cmd/certs.go

@@ -39,7 +39,6 @@ import (
 	kubeconfigphase "k8s.io/kubernetes/cmd/kubeadm/app/phases/kubeconfig"
 	configutil "k8s.io/kubernetes/cmd/kubeadm/app/util/config"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
-	"k8s.io/kubernetes/cmd/kubeadm/app/util/output"
 )
 
 var (
@@ -333,7 +332,7 @@ func getInternalCfg(cfgPath string, kubeconfigPath string, cfg kubeadmapiv1.Clus
 	if cfgPath == "" {
 		client, err := kubeconfigutil.ClientSetFromFile(kubeconfigPath)
 		if err == nil {
-			internalcfg, err := configutil.FetchInitConfigurationFromCluster(client, &output.TextPrinter{}, logPrefix, false, false)
+			internalcfg, err := configutil.FetchInitConfigurationFromCluster(client, nil, logPrefix, false, false)
 			if err == nil {
 				fmt.Println() // add empty line to separate the FetchInitConfigurationFromCluster output from the command output
 				return internalcfg, nil

cmd/kubeadm/app/cmd/config.go

@@ -371,7 +371,7 @@ func newCmdConfigImagesList(out io.Writer, mockK8sVersion *string) *cobra.Comman
 
 			printer, err := outputFlags.ToPrinter()
 			if err != nil {
-				return err
+				return errors.Wrap(err, "could not construct output printer")
 			}
 
 			imagesList, err := NewImagesList(cfgPath, externalcfg)
@@ -424,7 +424,7 @@ func (itp *imageTextPrinter) PrintObj(obj runtime.Object, writer io.Writer) erro
 // imageTextPrintFlags provides flags necessary for printing image in a text form.
 type imageTextPrintFlags struct{}
 
-// ToPrinter returns kubeadm printer for the text output format
+// ToPrinter returns a kubeadm printer for the text output format
 func (ipf *imageTextPrintFlags) ToPrinter(outputFormat string) (output.Printer, error) {
 	if outputFormat == output.TextOutput {
 		return &imageTextPrinter{}, nil

cmd/kubeadm/app/cmd/join.go

@@ -47,7 +47,6 @@ import (
 	"k8s.io/kubernetes/cmd/kubeadm/app/discovery"
 	configutil "k8s.io/kubernetes/cmd/kubeadm/app/util/config"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
-	"k8s.io/kubernetes/cmd/kubeadm/app/util/output"
 )
 
 var (
@@ -619,7 +618,7 @@ func fetchInitConfiguration(tlsBootstrapCfg *clientcmdapi.Config) (*kubeadmapi.I
 	}
 
 	// Fetches the init configuration
-	initConfiguration, err := configutil.FetchInitConfigurationFromCluster(tlsClient, &output.TextPrinter{}, "preflight", true, false)
+	initConfiguration, err := configutil.FetchInitConfigurationFromCluster(tlsClient, nil, "preflight", true, false)
 	if err != nil {
 		return nil, errors.Wrap(err, "unable to fetch the kubeadm-config ConfigMap")
 	}

cmd/kubeadm/app/cmd/reset.go

@@ -37,7 +37,6 @@ import (
 	cmdutil "k8s.io/kubernetes/cmd/kubeadm/app/cmd/util"
 	kubeadmconstants "k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	configutil "k8s.io/kubernetes/cmd/kubeadm/app/util/config"
-	"k8s.io/kubernetes/cmd/kubeadm/app/util/output"
 	utilruntime "k8s.io/kubernetes/cmd/kubeadm/app/util/runtime"
 )
 
@@ -99,7 +98,7 @@ func newResetData(cmd *cobra.Command, options *resetOptions, in io.Reader, out i
 	client, err := getClientset(options.kubeconfigPath, false)
 	if err == nil {
 		klog.V(1).Infof("[reset] Loaded client set from kubeconfig file: %s", options.kubeconfigPath)
-		cfg, err = configutil.FetchInitConfigurationFromCluster(client, &output.TextPrinter{}, "reset", false, false)
+		cfg, err = configutil.FetchInitConfigurationFromCluster(client, nil, "reset", false, false)
 		if err != nil {
 			klog.Warningf("[reset] Unable to fetch the kubeadm-config ConfigMap from cluster: %v", err)
 		}

cmd/kubeadm/app/cmd/token.go

@@ -169,7 +169,7 @@ func newCmdToken(out io.Writer, errW io.Writer) *cobra.Command {
 
 			printer, err := outputFlags.ToPrinter()
 			if err != nil {
-				return err
+				return errors.Wrap(err, "could not construct output printer")
 			}
 
 			return RunListTokens(out, errW, client, printer)
@@ -354,7 +354,7 @@ func (ttp *tokenTextPrinter) PrintObj(obj runtime.Object, writer io.Writer) erro
 // tokenTextPrintFlags provides flags necessary for printing bootstrap token in a text form.
 type tokenTextPrintFlags struct{}
 
-// ToPrinter returns kubeadm printer for the text output format
+// ToPrinter returns a kubeadm printer for the text output format
 func (tpf *tokenTextPrintFlags) ToPrinter(outputFormat string) (output.Printer, error) {
 	if outputFormat == output.TextOutput {
 		return &tokenTextPrinter{columns: []string{"TOKEN", "TTL", "EXPIRES", "USAGES", "DESCRIPTION", "EXTRA GROUPS"}}, nil

cmd/kubeadm/app/cmd/upgrade/common.go

@@ -137,12 +137,12 @@ func enforceRequirements(flags *applyPlanFlags, args []string, dryRun bool, upgr
 		if apierrors.IsNotFound(err) {
 			printer.Printf("[upgrade/config] In order to upgrade, a ConfigMap called %q in the %s namespace must exist.\n", constants.KubeadmConfigConfigMap, metav1.NamespaceSystem)
 			printer.Printf("[upgrade/config] Without this information, 'kubeadm upgrade' won't know how to configure your upgraded cluster.\n")
-			printer.Printf("\n")
+			printer.Println()
 			printer.Printf("[upgrade/config] Next steps:\n")
 			printer.Printf("\t- OPTION 1: Run 'kubeadm config upload from-flags' and specify the same CLI arguments you passed to 'kubeadm init' when you created your control-plane.\n")
 			printer.Printf("\t- OPTION 2: Run 'kubeadm config upload from-file' and specify the same config file you passed to 'kubeadm init' when you created your control-plane.\n")
 			printer.Printf("\t- OPTION 3: Pass a config file to 'kubeadm upgrade' using the --config flag.\n")
-			printer.Printf("\n")
+			printer.Println()
 			err = errors.Errorf("the ConfigMap %q in the %s namespace used for getting configuration information was not found", constants.KubeadmConfigConfigMap, metav1.NamespaceSystem)
 		}
 		return nil, nil, nil, errors.Wrap(err, "[upgrade/config] FATAL")

cmd/kubeadm/app/cmd/upgrade/diff.go

@@ -37,7 +37,6 @@ import (
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	configutil "k8s.io/kubernetes/cmd/kubeadm/app/util/config"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
-	"k8s.io/kubernetes/cmd/kubeadm/app/util/output"
 )
 
 type diffFlags struct {
@@ -119,7 +118,7 @@ func runDiff(flags *diffFlags, args []string) error {
 		if err != nil {
 			return errors.Wrapf(err, "couldn't create a Kubernetes client from file %q", flags.kubeConfigPath)
 		}
-		cfg, err = configutil.FetchInitConfigurationFromCluster(client, &output.TextPrinter{}, "upgrade/diff", false, false)
+		cfg, err = configutil.FetchInitConfigurationFromCluster(client, nil, "upgrade/diff", false, false)
 	}
 	if err != nil {
 		return err

cmd/kubeadm/app/cmd/upgrade/node.go

@@ -33,7 +33,6 @@ import (
 	"k8s.io/kubernetes/cmd/kubeadm/app/cmd/phases/workflow"
 	"k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	configutil "k8s.io/kubernetes/cmd/kubeadm/app/util/config"
-	"k8s.io/kubernetes/cmd/kubeadm/app/util/output"
 )
 
 // nodeOptions defines all the options exposed via flags by kubeadm upgrade node.
@@ -140,7 +139,7 @@ func newNodeData(cmd *cobra.Command, args []string, options *nodeOptions) (*node
 	// Fetches the cluster configuration
 	// NB in case of control-plane node, we are reading all the info for the node; in case of NOT control-plane node
 	//    (worker node), we are not reading local API address and the CRI socket from the node object
-	cfg, err := configutil.FetchInitConfigurationFromCluster(client, &output.TextPrinter{}, "upgrade", !isControlPlaneNode, false)
+	cfg, err := configutil.FetchInitConfigurationFromCluster(client, nil, "upgrade", !isControlPlaneNode, false)
 	if err != nil {
 		return nil, errors.Wrap(err, "unable to fetch the kubeadm-config ConfigMap")
 	}

cmd/kubeadm/app/cmd/upgrade/plan.go

@@ -34,6 +34,7 @@ import (
 	"k8s.io/cli-runtime/pkg/printers"
 	clientset "k8s.io/client-go/kubernetes"
 	"k8s.io/klog/v2"
+
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
 	outputapischeme "k8s.io/kubernetes/cmd/kubeadm/app/apis/output/scheme"
 	outputapiv1alpha2 "k8s.io/kubernetes/cmd/kubeadm/app/apis/output/v1alpha2"
@@ -62,7 +63,7 @@ func newCmdPlan(apf *applyPlanFlags) *cobra.Command {
 		RunE: func(_ *cobra.Command, args []string) error {
 			printer, err := outputFlags.ToPrinter()
 			if err != nil {
-				return err
+				return errors.Wrap(err, "could not construct output printer")
 			}
 
 			return runPlan(flags, args, printer)
@@ -77,21 +78,21 @@ func newCmdPlan(apf *applyPlanFlags) *cobra.Command {
 }
 
 // newComponentUpgradePlan helper creates outputapiv1alpha2.ComponentUpgradePlan object
-func newComponentUpgradePlan(name, currentVersion, newVersion string) *outputapiv1alpha2.ComponentUpgradePlan {
+func newComponentUpgradePlan(name, currentVersion, newVersion string) outputapiv1alpha2.ComponentUpgradePlan {
-	return &outputapiv1alpha2.ComponentUpgradePlan{
+	return outputapiv1alpha2.ComponentUpgradePlan{
 		Name:           name,
 		CurrentVersion: currentVersion,
 		NewVersion:     newVersion,
 	}
 }
 
-// upgradePlanPrintFlags defines printer flag structure for the
+// upgradePlanPrintFlags defines a printer flag structure for the
 // upgrade plan kubeadm command and provides a method
 // of retrieving a known printer based on flag values provided.
 type upgradePlanPrintFlags struct {
-	// JSONYamlPrintFlags provides default flags necessary for json/yaml printing.
+	// JSONYamlPrintFlags provides default flags necessary for json/yaml printing
 	JSONYamlPrintFlags *upgradePlanJSONYamlPrintFlags
-	// TextPrintFlags provides default flags necessary for text printing.
+	// TextPrintFlags provides default flags necessary for text printing
 	TextPrintFlags *upgradePlanTextPrintFlags
 	// TypeSetterPrinter is an implementation of ResourcePrinter that wraps another printer with types set on the objects
 	TypeSetterPrinter *printers.TypeSetterPrinter
@@ -108,7 +109,7 @@ func newUpgradePlanPrintFlags(outputFormat string) *upgradePlanPrintFlags {
 	}
 }
 
-// AllowedFormats returns list of allowed output formats
+// AllowedFormats returns a list of allowed output formats
 func (pf *upgradePlanPrintFlags) AllowedFormats() []string {
 	ret := pf.TextPrintFlags.AllowedFormats()
 	return append(ret, pf.JSONYamlPrintFlags.AllowedFormats()...)
@@ -119,7 +120,9 @@ func (pf *upgradePlanPrintFlags) AllowedFormats() []string {
 func (pf *upgradePlanPrintFlags) AddFlags(cmd *cobra.Command) {
 	pf.TextPrintFlags.AddFlags(cmd)
 	pf.JSONYamlPrintFlags.AddFlags(cmd)
-	cmd.Flags().StringVarP(&pf.OutputFormat, "experimental-output", "o", pf.OutputFormat, fmt.Sprintf("Output format. One of: %s.", strings.Join(pf.AllowedFormats(), "|")))
+	// TODO: once we are confident the feature is graduated we should remove the EXPERIMENTAL text below:
+	// https://github.com/kubernetes/kubeadm/issues/494
+	cmd.Flags().StringVarP(&pf.OutputFormat, "output", "o", pf.OutputFormat, fmt.Sprintf("EXPERIMENTAL: Output format. One of: %s.", strings.Join(pf.AllowedFormats(), "|")))
 }
 
 // ToPrinter receives an outputFormat and returns a printer capable of
@@ -142,7 +145,7 @@ type upgradePlanJSONYamlPrintFlags struct {
 	genericclioptions.JSONYamlPrintFlags
 }
 
-// AllowedFormats returns list of allowed output formats
+// AllowedFormats returns a list of allowed output formats
 func (pf *upgradePlanJSONYamlPrintFlags) AllowedFormats() []string {
 	return []string{output.JSONOutput, output.YAMLOutput}
 }
@@ -150,10 +153,10 @@ func (pf *upgradePlanJSONYamlPrintFlags) AllowedFormats() []string {
 // upgradePlanJSONYAMLPrinter prints upgrade plan in a JSON or YAML format
 type upgradePlanJSONYAMLPrinter struct {
 	output.ResourcePrinterWrapper
-	Buffer []*outputapiv1alpha2.ComponentUpgradePlan
+	Buffer []outputapiv1alpha2.ComponentUpgradePlan
 }
 
-// newUpgradePlanJSONYAMLPrinter creates new upgradePlanJSONYAMLPrinter object
+// newUpgradePlanJSONYAMLPrinter creates a new upgradePlanJSONYAMLPrinter object
 func newUpgradePlanJSONYAMLPrinter(resourcePrinter printers.ResourcePrinter, err error) (output.Printer, error) {
 	if err != nil {
 		return nil, err
@@ -165,18 +168,29 @@ func newUpgradePlanJSONYAMLPrinter(resourcePrinter printers.ResourcePrinter, err
 func (p *upgradePlanJSONYAMLPrinter) PrintObj(obj runtime.Object, writer io.Writer) error {
 	item, ok := obj.(*outputapiv1alpha2.ComponentUpgradePlan)
 	if !ok {
-		return fmt.Errorf("expected ComponentUpgradePlan, but got %+v", obj)
+		return errors.Errorf("expected ComponentUpgradePlan, but got %+v", obj)
 	}
-	p.Buffer = append(p.Buffer, item)
+	p.Buffer = append(p.Buffer, *item)
 	return nil
 }
 
-// Close writes any buffered data and empties list of buffered components
+// Flush writes any buffered data once last object is added
-func (p *upgradePlanJSONYAMLPrinter) Close(writer io.Writer) {
+func (p *upgradePlanJSONYAMLPrinter) Flush(writer io.Writer, last bool) {
+	if !last {
+		return
+	}
+	if len(p.Buffer) == 0 {
+		return
+	}
 	plan := &outputapiv1alpha2.UpgradePlan{Components: p.Buffer}
-	// p.ResourcePrinterWrapper.Printer.PrintObj(plan, writer)
+	if err := p.Printer.PrintObj(plan, writer); err != nil {
-	p.Printer.PrintObj(plan, writer)
+		fmt.Fprintf(os.Stderr, "could not flush output buffer: %v\n", err)
-	p.Buffer = []*outputapiv1alpha2.ComponentUpgradePlan{}
+	}
+}
+
+// Close empties the list of buffered components
+func (p *upgradePlanJSONYAMLPrinter) Close(writer io.Writer) {
+	p.Buffer = p.Buffer[:0]
 }
 
 // upgradePlanTextPrinter prints upgrade plan in a text form
@@ -187,10 +201,11 @@ type upgradePlanTextPrinter struct {
 }
 
 // Flush writes any buffered data
-func (p *upgradePlanTextPrinter) Flush(writer io.Writer) {
+func (p *upgradePlanTextPrinter) Flush(writer io.Writer, last bool) {
 	if p.tabwriter != nil {
 		p.tabwriter.Flush()
 		p.tabwriter = nil
+		p.Fprintln(writer, "")
 	}
 }
 
@@ -204,26 +219,25 @@ func (p *upgradePlanTextPrinter) PrintObj(obj runtime.Object, writer io.Writer)
 
 	item, ok := obj.(*outputapiv1alpha2.ComponentUpgradePlan)
 	if !ok {
-		return fmt.Errorf("expected ComponentUpgradePlan, but got %+v", obj)
+		return errors.Errorf("expected ComponentUpgradePlan, but got %+v", obj)
 	}
 
 	// Print item
 	fmt.Fprintf(p.tabwriter, "%s\t%s\t%s\n", item.Name, item.CurrentVersion, item.NewVersion)
-
 	return nil
 }
 
-// upgradePlanTextPrintFlags provides flags necessary for printing upgrade plan in a text form.
+// upgradePlanTextPrintFlags provides flags necessary for printing upgrade plan in a text form
 type upgradePlanTextPrintFlags struct{}
 
 func (pf *upgradePlanTextPrintFlags) AddFlags(cmd *cobra.Command) {}
 
-// AllowedFormats returns list of allowed output formats
+// AllowedFormats returns a list of allowed output formats
 func (pf *upgradePlanTextPrintFlags) AllowedFormats() []string {
 	return []string{output.TextOutput}
 }
 
-// ToPrinter returns kubeadm printer for the text output format
+// ToPrinter returns a kubeadm printer for the text output format
 func (pf *upgradePlanTextPrintFlags) ToPrinter(outputFormat string) (output.Printer, error) {
 	if outputFormat == output.TextOutput {
 		return &upgradePlanTextPrinter{columns: []string{"COMPONENT", "CURRENT", "TARGET"}}, nil
@@ -282,15 +296,12 @@ func runPlan(flags *planFlags, args []string, printer output.Printer) error {
 
 	// Finally, print the component config state table
 	printComponentConfigVersionStates(configVersionStates, os.Stdout, printer)
-
-	// Add a newline in the end of this output to leave some space to the next output section
-	klog.V(1).Infoln()
 	return nil
 }
 
 // TODO There is currently no way to cleanly output upgrades that involve adding, removing, or changing components
 // https://github.com/kubernetes/kubeadm/issues/810 was created to track addressing this.
-func appendDNSComponent(components []*outputapiv1alpha2.ComponentUpgradePlan, up *upgrade.Upgrade, name string) []*outputapiv1alpha2.ComponentUpgradePlan {
+func appendDNSComponent(components []outputapiv1alpha2.ComponentUpgradePlan, up *upgrade.Upgrade, name string) []outputapiv1alpha2.ComponentUpgradePlan {
 	beforeVersion := up.Before.DNSVersion
 	afterVersion := up.After.DNSVersion
 
@@ -316,7 +327,7 @@ func genUpgradePlan(up *upgrade.Upgrade, isExternalEtcd bool) (*outputapiv1alpha
 		}
 	}
 
-	components := []*outputapiv1alpha2.ComponentUpgradePlan{}
+	components := []outputapiv1alpha2.ComponentUpgradePlan{}
 
 	if up.CanUpgradeKubelets() {
 		// The map is of the form <old-version>:<node-count>. Here all the keys are put into a slice and sorted
@@ -370,26 +381,26 @@ func printUpgradePlan(up *upgrade.Upgrade, plan *outputapiv1alpha2.UpgradePlan,
 		} else if component.Name == constants.Kubelet {
 			if printManualUpgradeHeader {
 				printer.Fprintln(writer, "Components that must be upgraded manually after you have upgraded the control plane with 'kubeadm upgrade apply':")
-				printer.PrintObj(newComponentUpgradePlan(component.Name, component.CurrentVersion, component.NewVersion), writer)
+				plan := newComponentUpgradePlan(component.Name, component.CurrentVersion, component.NewVersion)
+				printer.PrintObj(&plan, writer)
 				printManualUpgradeHeader = false
 			} else {
-				printer.PrintObj(newComponentUpgradePlan("", component.CurrentVersion, component.NewVersion), writer)
+				plan := newComponentUpgradePlan("", component.CurrentVersion, component.NewVersion)
+				printer.PrintObj(&plan, writer)
 			}
 		} else {
 			if printHeader {
 				// End of manual upgrades table
-				printer.Flush(writer)
+				printer.Flush(writer, false)
-
-				printer.Fprintln(writer, "")
 				printer.Fprintf(writer, "Upgrade to the latest %s:\n", up.Description)
 				printer.Fprintln(writer, "")
 				printHeader = false
 			}
-			printer.PrintObj(newComponentUpgradePlan(component.Name, component.CurrentVersion, component.NewVersion), writer)
+			plan := newComponentUpgradePlan(component.Name, component.CurrentVersion, component.NewVersion)
+			printer.PrintObj(&plan, writer)
 		}
 	}
-	printer.Flush(writer)
+	printer.Flush(writer, true)
-	printer.Fprintln(writer, "")
 
 	printer.Fprintln(writer, "You can now apply the upgrade by executing the following command:")
 	printer.Fprintln(writer, "")
@@ -430,8 +441,7 @@ func yesOrNo(b bool) string {
 }
 
 func printLineSeparator(w io.Writer, printer output.Printer) {
-	printer.Fprintln(w, "_____________________________________________________________________")
+	printer.Fprintf(w, "_____________________________________________________________________\n\n")
-	printer.Fprintln(w, "")
 }
 
 func printComponentConfigVersionStates(versionStates []outputapiv1alpha2.ComponentConfigVersionState, w io.Writer, printer output.Printer) {

cmd/kubeadm/app/componentconfigs/configset.go

@@ -26,9 +26,9 @@ import (
 	"k8s.io/apimachinery/pkg/util/validation/field"
 	clientset "k8s.io/client-go/kubernetes"
 	"k8s.io/klog/v2"
-	outputapiv1alpha2 "k8s.io/kubernetes/cmd/kubeadm/app/apis/output/v1alpha2"
 
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
+	outputapiv1alpha2 "k8s.io/kubernetes/cmd/kubeadm/app/apis/output/v1alpha2"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	"k8s.io/kubernetes/cmd/kubeadm/app/util/apiclient"
 	"k8s.io/kubernetes/cmd/kubeadm/app/util/config/strict"

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

@@ -268,7 +268,7 @@ func GetAvailableUpgrades(versionGetterImpl VersionGetter, experimentalUpgradesA
 	}
 
 	// Add a newline in the end of this output to leave some space to the next output section
-	printer.Printf("\n")
+	printer.Println()
 
 	return upgrades, nil
 }

cmd/kubeadm/app/util/config/cluster.go

@@ -46,6 +46,9 @@ import (
 
 // FetchInitConfigurationFromCluster fetches configuration from a ConfigMap in the cluster
 func FetchInitConfigurationFromCluster(client clientset.Interface, printer output.Printer, logPrefix string, newControlPlane, skipComponentConfigs bool) (*kubeadmapi.InitConfiguration, error) {
+	if printer == nil {
+		printer = &output.TextPrinter{}
+	}
 	printer.Printf("[%s] Reading configuration from the cluster...\n", logPrefix)
 	printer.Printf("[%s] FYI: You can look at this config file with 'kubectl -n %s get cm %s -o yaml'\n", logPrefix, metav1.NamespaceSystem, constants.KubeadmConfigConfigMap)
 

cmd/kubeadm/app/util/output/output.go

@@ -28,14 +28,16 @@ import (
 	"k8s.io/cli-runtime/pkg/printers"
 )
 
-// TextOutput describes the plain text output
+const (
-const TextOutput = "text"
+	// TextOutput describes the plain text output
+	TextOutput = "text"
 
-// JSONOutput describes the JSON output
+	// JSONOutput describes the JSON output
-const JSONOutput = "json"
+	JSONOutput = "json"
 
-// YAMLOutput describes the YAML output
+	// YAMLOutput describes the YAML output
-const YAMLOutput = "yaml"
+	YAMLOutput = "yaml"
+)
 
 // TextPrintFlags is an interface to handle custom text output
 type TextPrintFlags interface {
@@ -58,7 +60,7 @@ type PrintFlags struct {
 	OutputFormat *string
 }
 
-// AllowedFormats returns list of allowed output formats
+// AllowedFormats returns a list of allowed output formats
 func (pf *PrintFlags) AllowedFormats() []string {
 	ret := []string{TextOutput}
 	ret = append(ret, pf.JSONYamlPrintFlags.AllowedFormats()...)
@@ -141,8 +143,9 @@ type Printer interface {
 	Fprintf(writer io.Writer, format string, args ...interface{}) (n int, err error)
 	Fprintln(writer io.Writer, args ...interface{}) (n int, err error)
 	Printf(format string, args ...interface{}) (n int, err error)
+	Println(args ...interface{}) (n int, err error)
 
-	Flush(writer io.Writer)
+	Flush(writer io.Writer, last bool)
 	Close(writer io.Writer)
 }
 
@@ -150,16 +153,6 @@ type Printer interface {
 type TextPrinter struct {
 }
 
-// Flush writes any buffered data
-func (tp *TextPrinter) Flush(writer io.Writer) {
-	return
-}
-
-// Close flushes any buffered data and closes the printer
-func (tp *TextPrinter) Close(writer io.Writer) {
-	return
-}
-
 // PrintObj is an implementation of ResourcePrinter.PrintObj that prints object
 func (tp *TextPrinter) PrintObj(obj runtime.Object, writer io.Writer) error {
 	_, err := fmt.Fprintf(writer, "%+v\n", obj)
@@ -181,6 +174,19 @@ func (tp *TextPrinter) Printf(format string, args ...interface{}) (n int, err er
 	return fmt.Printf(format, args...)
 }
 
+// Println is a wrapper around fmt.Printf
+func (tp *TextPrinter) Println(args ...interface{}) (n int, err error) {
+	return fmt.Println(args...)
+}
+
+// Flush writes any buffered data
+func (tp *TextPrinter) Flush(writer io.Writer, last bool) {
+}
+
+// Close flushes any buffered data and closes the printer
+func (tp *TextPrinter) Close(writer io.Writer) {
+}
+
 // ResourcePrinterWrapper wraps ResourcePrinter and implements Printer interface
 type ResourcePrinterWrapper struct {
 	Printer printers.ResourcePrinter
@@ -195,13 +201,11 @@ func NewResourcePrinterWrapper(resourcePrinter printers.ResourcePrinter, err err
 }
 
 // Flush writes any buffered data
-func (rpw *ResourcePrinterWrapper) Flush(writer io.Writer) {
+func (rpw *ResourcePrinterWrapper) Flush(writer io.Writer, last bool) {
-	return
 }
 
 // Close flushes any buffered data and closes the printer
 func (rpw *ResourcePrinterWrapper) Close(writer io.Writer) {
-	return
 }
 
 // PrintObj is an implementation of ResourcePrinter.PrintObj that calls underlying printer API
@@ -216,7 +220,7 @@ func (rpw *ResourcePrinterWrapper) Fprintf(writer io.Writer, format string, args
 	return 0, nil
 }
 
-// Fprintln is an empty method to satisfy Printer interface
+// Fprintln is an empty method to satisfy the Printer interface
 // and silent info printing for structured output
 // This method is usually redefined for the text output
 func (rpw *ResourcePrinterWrapper) Fprintln(writer io.Writer, args ...interface{}) (n int, err error) {
@@ -229,3 +233,10 @@ func (rpw *ResourcePrinterWrapper) Fprintln(writer io.Writer, args ...interface{
 func (rpw *ResourcePrinterWrapper) Printf(format string, args ...interface{}) (n int, err error) {
 	return 0, nil
 }
+
+// Println is an empty method to satisfy Printer interface
+// and silent info printing for structured output
+// This method is usually redefined for the text output
+func (rpw *ResourcePrinterWrapper) Println(args ...interface{}) (n int, err error) {
+	return 0, nil
+}