Merge pull request #73732 from yagonobre/kubelet-start

kubeadm: graduate kubelet start join phase

cmd/kubeadm/app/cmd/BUILD

@@ -42,9 +42,7 @@ go_library(
         "//cmd/kubeadm/app/phases/certs:go_default_library",
         "//cmd/kubeadm/app/phases/etcd:go_default_library",
         "//cmd/kubeadm/app/phases/kubeconfig:go_default_library",
-        "//cmd/kubeadm/app/phases/kubelet:go_default_library",
         "//cmd/kubeadm/app/phases/markcontrolplane:go_default_library",
-        "//cmd/kubeadm/app/phases/patchnode:go_default_library",
         "//cmd/kubeadm/app/phases/uploadconfig:go_default_library",
         "//cmd/kubeadm/app/preflight:go_default_library",
         "//cmd/kubeadm/app/util:go_default_library",
@@ -59,11 +57,9 @@ go_library(
         "//staging/src/k8s.io/apimachinery/pkg/fields:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/duration:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/sets:go_default_library",
-        "//staging/src/k8s.io/apimachinery/pkg/util/wait:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/version:go_default_library",
         "//staging/src/k8s.io/client-go/kubernetes:go_default_library",
         "//staging/src/k8s.io/client-go/tools/clientcmd/api:go_default_library",
-        "//staging/src/k8s.io/client-go/util/cert:go_default_library",
         "//staging/src/k8s.io/cluster-bootstrap/token/api:go_default_library",
         "//staging/src/k8s.io/cluster-bootstrap/token/util:go_default_library",
         "//vendor/github.com/lithammer/dedent:go_default_library",

cmd/kubeadm/app/cmd/join.go

@@ -1,5 +1,5 @@
 /*
-Copyright 2016 The Kubernetes Authors.
+Copyright 2019 The Kubernetes Authors.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -28,10 +28,8 @@ import (
 	"github.com/spf13/cobra"
 	flag "github.com/spf13/pflag"
 	"k8s.io/apimachinery/pkg/util/sets"
-	"k8s.io/apimachinery/pkg/util/wait"
 	clientset "k8s.io/client-go/kubernetes"
 	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
-	certutil "k8s.io/client-go/util/cert"
 	"k8s.io/klog"
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
 	kubeadmscheme "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/scheme"
@@ -44,16 +42,11 @@ import (
 	kubeadmconstants "k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	"k8s.io/kubernetes/cmd/kubeadm/app/discovery"
 	etcdphase "k8s.io/kubernetes/cmd/kubeadm/app/phases/etcd"
-	kubeletphase "k8s.io/kubernetes/cmd/kubeadm/app/phases/kubelet"
 	markcontrolplanephase "k8s.io/kubernetes/cmd/kubeadm/app/phases/markcontrolplane"
-	patchnodephase "k8s.io/kubernetes/cmd/kubeadm/app/phases/patchnode"
 	uploadconfigphase "k8s.io/kubernetes/cmd/kubeadm/app/phases/uploadconfig"
-	"k8s.io/kubernetes/cmd/kubeadm/app/preflight"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
-	"k8s.io/kubernetes/cmd/kubeadm/app/util/apiclient"
 	configutil "k8s.io/kubernetes/cmd/kubeadm/app/util/config"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
-	utilsexec "k8s.io/utils/exec"
 )
 
 var (
@@ -127,19 +120,6 @@ var (
 		Often times the same token is used for both parts. In this case, the
 		--token flag can be used instead of specifying each token individually.
 		`)
-
-	kubeadmJoinFailMsg = dedent.Dedent(`
-		Unfortunately, an error has occurred:
-			%v
-
-		This error is likely caused by:
-			- The kubelet is not running
-			- The kubelet is unhealthy due to a misconfiguration of the node in some way (required cgroups disabled)
-
-		If you are on a systemd-powered system, you can try to troubleshoot the error with the following commands:
-			- 'systemctl status kubelet'
-			- 'journalctl -xeu kubelet'
-		`)
 )
 
 // joinOptions defines all the options exposed via flags by kubeadm join.
@@ -201,6 +181,7 @@ func NewCmdJoin(out io.Writer, joinOptions *joinOptions) *cobra.Command {
 	joinRunner.AppendPhase(phases.NewPreflightPhase())
 	joinRunner.AppendPhase(phases.NewControlPlanePreparePhase())
 	joinRunner.AppendPhase(phases.NewCheckEtcdPhase())
+	joinRunner.AppendPhase(phases.NewKubeletStartPhase())
 
 	// sets the data builder function, that will be used by the runner
 	// both when running the entire workflow or single phases
@@ -438,25 +419,11 @@ func (j *joinData) Run() error {
 	// TODO: individual phases should call these:
 	//   - phases that need initCfg should call joinData.InitCfg().
 	//   - phases that need tlsBootstrapCfg should call joinData.TLSBootstrapCfg().
-	tlsBootstrapCfg, err := j.TLSBootstrapCfg()
-	if err != nil {
-		return err
-	}
 	initCfg, err := j.InitCfg()
 	if err != nil {
 		return err
 	}
 
-	// Executes the kubelet TLS bootstrap process, that completes with the node
-	// joining the cluster with a dedicates set of credentials as required by
-	// the node authorizer.
-	// if the node is hosting a new control plane instance, since it uses static pods for the control plane,
-	// as soon as the kubelet starts it will take charge of creating control plane
-	// components on the node.
-	if err := j.BootstrapKubelet(tlsBootstrapCfg, initCfg); err != nil {
-		return err
-	}
-
 	// if the node is hosting a new control plane instance
 	if j.cfg.ControlPlane != nil {
 		// Completes the control plane setup
@@ -485,81 +452,6 @@ func (j *joinData) Run() error {
 	return nil
 }
 
-// BootstrapKubelet executes the kubelet TLS bootstrap process.
-// This process is executed by the kubelet and completes with the node joining the cluster
-// with a dedicates set of credentials as required by the node authorizer
-func (j *joinData) BootstrapKubelet(tlsBootstrapCfg *clientcmdapi.Config, initConfiguration *kubeadmapi.InitConfiguration) error {
-	bootstrapKubeConfigFile := kubeadmconstants.GetBootstrapKubeletKubeConfigPath()
-
-	// Write the bootstrap kubelet config file or the TLS-Boostrapped kubelet config file down to disk
-	klog.V(1).Infoln("[join] writing bootstrap kubelet config file at", bootstrapKubeConfigFile)
-	if err := kubeconfigutil.WriteToDisk(bootstrapKubeConfigFile, tlsBootstrapCfg); err != nil {
-		return errors.Wrap(err, "couldn't save bootstrap-kubelet.conf to disk")
-	}
-
-	// Write the ca certificate to disk so kubelet can use it for authentication
-	cluster := tlsBootstrapCfg.Contexts[tlsBootstrapCfg.CurrentContext].Cluster
-	if _, err := os.Stat(j.cfg.CACertPath); os.IsNotExist(err) {
-		if err := certutil.WriteCert(j.cfg.CACertPath, tlsBootstrapCfg.Clusters[cluster].CertificateAuthorityData); err != nil {
-			return errors.Wrap(err, "couldn't save the CA certificate to disk")
-		}
-	}
-
-	kubeletVersion, err := preflight.GetKubeletVersion(utilsexec.New())
-	if err != nil {
-		return err
-	}
-
-	bootstrapClient, err := kubeconfigutil.ClientSetFromFile(bootstrapKubeConfigFile)
-	if err != nil {
-		return errors.Errorf("couldn't create client from kubeconfig file %q", bootstrapKubeConfigFile)
-	}
-
-	// Configure the kubelet. In this short timeframe, kubeadm is trying to stop/restart the kubelet
-	// Try to stop the kubelet service so no race conditions occur when configuring it
-	klog.V(1).Infof("Stopping the kubelet")
-	kubeletphase.TryStopKubelet()
-
-	// Write the configuration for the kubelet (using the bootstrap token credentials) to disk so the kubelet can start
-	if err := kubeletphase.DownloadConfig(bootstrapClient, kubeletVersion, kubeadmconstants.KubeletRunDirectory); err != nil {
-		return err
-	}
-
-	// Write env file with flags for the kubelet to use. We only want to
-	// register the joining node with the specified taints if the node
-	// is not a master. The markmaster phase will register the taints otherwise.
-	registerTaintsUsingFlags := j.cfg.ControlPlane == nil
-	if err := kubeletphase.WriteKubeletDynamicEnvFile(&initConfiguration.ClusterConfiguration, &initConfiguration.NodeRegistration, registerTaintsUsingFlags, kubeadmconstants.KubeletRunDirectory); err != nil {
-		return err
-	}
-
-	// Try to start the kubelet service in case it's inactive
-	klog.V(1).Infof("Starting the kubelet")
-	kubeletphase.TryStartKubelet()
-
-	// Now the kubelet will perform the TLS Bootstrap, transforming /etc/kubernetes/bootstrap-kubelet.conf to /etc/kubernetes/kubelet.conf
-	// Wait for the kubelet to create the /etc/kubernetes/kubelet.conf kubeconfig file. If this process
-	// times out, display a somewhat user-friendly message.
-	waiter := apiclient.NewKubeWaiter(nil, kubeadmconstants.TLSBootstrapTimeout, os.Stdout)
-	if err := waiter.WaitForKubeletAndFunc(waitForTLSBootstrappedClient); err != nil {
-		fmt.Printf(kubeadmJoinFailMsg, err)
-		return err
-	}
-
-	// When we know the /etc/kubernetes/kubelet.conf file is available, get the client
-	client, err := kubeconfigutil.ClientSetFromFile(kubeadmconstants.GetKubeletKubeConfigPath())
-	if err != nil {
-		return err
-	}
-
-	klog.V(1).Infof("[join] preserving the crisocket information for the node")
-	if err := patchnodephase.AnnotateCRISocket(client, j.cfg.NodeRegistration.Name, j.cfg.NodeRegistration.CRISocket); err != nil {
-		return errors.Wrap(err, "error uploading crisocket")
-	}
-
-	return nil
-}
-
 // PostInstallControlPlane marks the new node as master and update the cluster status with information about current node
 func (j *joinData) PostInstallControlPlane(initConfiguration *kubeadmapi.InitConfiguration) error {
 	kubeConfigFile := filepath.Join(kubeadmconstants.KubernetesDir, kubeadmconstants.AdminKubeConfigFileName)
@@ -599,20 +491,6 @@ func (j *joinData) PostInstallControlPlane(initConfiguration *kubeadmapi.InitCon
 	return nil
 }
 
-// waitForTLSBootstrappedClient waits for the /etc/kubernetes/kubelet.conf file to be available
-func waitForTLSBootstrappedClient() error {
-	fmt.Println("[tlsbootstrap] Waiting for the kubelet to perform the TLS Bootstrap...")
-
-	// Loop on every falsy return. Return with an error if raised. Exit successfully if true is returned.
-	return wait.PollImmediate(kubeadmconstants.APICallRetryInterval, kubeadmconstants.TLSBootstrapTimeout, func() (bool, error) {
-		// Check that we can create a client set out of the kubelet kubeconfig. This ensures not
-		// only that the kubeconfig file exists, but that other files required by it also exist (like
-		// client certificate and key)
-		_, err := kubeconfigutil.ClientSetFromFile(kubeadmconstants.GetKubeletKubeConfigPath())
-		return (err == nil), nil
-	})
-}
-
 // fetchInitConfigurationFromJoinConfiguration retrieves the init configuration from a join configuration, performing the discovery
 func fetchInitConfigurationFromJoinConfiguration(cfg *kubeadmapi.JoinConfiguration, tlsBootstrapCfg *clientcmdapi.Config) (*kubeadmapi.InitConfiguration, error) {
 	// Retrieves the kubeadm configuration

cmd/kubeadm/app/cmd/phases/init/kubelet.go

@@ -1,5 +1,5 @@
 /*
-Copyright 2018 The Kubernetes Authors.
+Copyright 2019 The Kubernetes Authors.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -29,7 +29,7 @@ import (
 var (
 	kubeletStartPhaseExample = normalizer.Examples(`
 		# Writes a dynamic environment file with kubelet flags from a InitConfiguration file.
-		kubeadm init phase kubelet-start --config masterconfig.yaml
+		kubeadm init phase kubelet-start --config config.yaml
 		`)
 )
 

cmd/kubeadm/app/cmd/phases/join/BUILD

@@ -5,6 +5,7 @@ go_library(
     srcs = [
         "checketcd.go",
         "controlplane.go",
+        "kubelet.go",
         "preflight.go",
     ],
     importpath = "k8s.io/kubernetes/cmd/kubeadm/app/cmd/phases/join",
@@ -19,10 +20,17 @@ go_library(
         "//cmd/kubeadm/app/phases/controlplane:go_default_library",
         "//cmd/kubeadm/app/phases/etcd:go_default_library",
         "//cmd/kubeadm/app/phases/kubeconfig:go_default_library",
+        "//cmd/kubeadm/app/phases/kubelet:go_default_library",
+        "//cmd/kubeadm/app/phases/patchnode:go_default_library",
         "//cmd/kubeadm/app/preflight:go_default_library",
+        "//cmd/kubeadm/app/util/apiclient:go_default_library",
+        "//cmd/kubeadm/app/util/kubeconfig:go_default_library",
         "//pkg/util/normalizer:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/sets:go_default_library",
+        "//staging/src/k8s.io/apimachinery/pkg/util/wait:go_default_library",
         "//staging/src/k8s.io/client-go/kubernetes:go_default_library",
+        "//staging/src/k8s.io/client-go/tools/clientcmd/api:go_default_library",
+        "//staging/src/k8s.io/client-go/util/cert:go_default_library",
         "//vendor/github.com/lithammer/dedent:go_default_library",
         "//vendor/github.com/pkg/errors:go_default_library",
         "//vendor/k8s.io/klog:go_default_library",

cmd/kubeadm/app/cmd/phases/join/controlplane.go

@@ -21,7 +21,6 @@ import (
 
 	"github.com/pkg/errors"
 
-	clientset "k8s.io/client-go/kubernetes"
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
 	"k8s.io/kubernetes/cmd/kubeadm/app/cmd/options"
 	"k8s.io/kubernetes/cmd/kubeadm/app/cmd/phases/workflow"
@@ -34,7 +33,6 @@ import (
 
 type controlPlanePrepareData interface {
 	Cfg() *kubeadmapi.JoinConfiguration
-	ClientSetFromFile(string) (*clientset.Clientset, error)
 	InitCfg() (*kubeadmapi.InitConfiguration, error)
 }
 

cmd/kubeadm/app/cmd/phases/join/kubelet.go

@@ -0,0 +1,192 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package phases
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/lithammer/dedent"
+	"github.com/pkg/errors"
+	"k8s.io/apimachinery/pkg/util/wait"
+	clientset "k8s.io/client-go/kubernetes"
+	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
+	certutil "k8s.io/client-go/util/cert"
+	"k8s.io/klog"
+	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
+	"k8s.io/kubernetes/cmd/kubeadm/app/cmd/options"
+	"k8s.io/kubernetes/cmd/kubeadm/app/cmd/phases/workflow"
+	kubeadmconstants "k8s.io/kubernetes/cmd/kubeadm/app/constants"
+	kubeletphase "k8s.io/kubernetes/cmd/kubeadm/app/phases/kubelet"
+	patchnodephase "k8s.io/kubernetes/cmd/kubeadm/app/phases/patchnode"
+	"k8s.io/kubernetes/cmd/kubeadm/app/preflight"
+	"k8s.io/kubernetes/cmd/kubeadm/app/util/apiclient"
+	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
+	utilsexec "k8s.io/utils/exec"
+)
+
+var (
+	kubeadmJoinFailMsg = dedent.Dedent(`
+		Unfortunately, an error has occurred:
+			%v
+
+		This error is likely caused by:
+			- The kubelet is not running
+			- The kubelet is unhealthy due to a misconfiguration of the node in some way (required cgroups disabled)
+
+		If you are on a systemd-powered system, you can try to troubleshoot the error with the following commands:
+			- 'systemctl status kubelet'
+			- 'journalctl -xeu kubelet'
+		`)
+)
+
+type kubeletStartData interface {
+	Cfg() *kubeadmapi.JoinConfiguration
+	ClientSetFromFile(path string) (*clientset.Clientset, error)
+	InitCfg() (*kubeadmapi.InitConfiguration, error)
+	TLSBootstrapCfg() (*clientcmdapi.Config, error)
+}
+
+// NewKubeletStartPhase creates a kubeadm workflow phase that start kubelet on a node.
+func NewKubeletStartPhase() workflow.Phase {
+	return workflow.Phase{
+		Name:  "kubelet-start",
+		Short: "Writes kubelet settings, certificates and (re)starts the kubelet",
+		Long:  "Writes a file with KubeletConfiguration and an environment file with node specific kubelet settings, and then (re)starts kubelet.",
+		Run:   runKubeletStartJoinPhase,
+		InheritFlags: []string{
+			options.CfgPath,
+			options.NodeCRISocket,
+			options.NodeName,
+			options.TLSBootstrapToken,
+			options.TokenDiscovery,
+			options.TokenDiscoveryCAHash,
+			options.TokenDiscoverySkipCAHash,
+			options.TokenStr,
+		},
+	}
+}
+
+func getKubeletStartJoinData(c workflow.RunData) (kubeletStartData, *kubeadmapi.JoinConfiguration, *kubeadmapi.InitConfiguration, *clientcmdapi.Config, error) {
+	data, ok := c.(kubeletStartData)
+	if !ok {
+		return nil, nil, nil, nil, errors.New("kubelet-start phase invoked with an invalid data struct")
+	}
+	cfg := data.Cfg()
+	initCfg, err := data.InitCfg()
+	if err != nil {
+		return nil, nil, nil, nil, err
+	}
+	tlsBootstrapCfg, err := data.TLSBootstrapCfg()
+	if err != nil {
+		return nil, nil, nil, nil, err
+	}
+	return data, cfg, initCfg, tlsBootstrapCfg, nil
+}
+
+// runKubeletStartJoinPhase executes the kubelet TLS bootstrap process.
+// This process is executed by the kubelet and completes with the node joining the cluster
+// with a dedicates set of credentials as required by the node authorizer
+func runKubeletStartJoinPhase(c workflow.RunData) error {
+	data, cfg, initCfg, tlsBootstrapCfg, err := getKubeletStartJoinData(c)
+	if err != nil {
+		return err
+	}
+	bootstrapKubeConfigFile := kubeadmconstants.GetBootstrapKubeletKubeConfigPath()
+
+	// Write the bootstrap kubelet config file or the TLS-Boostrapped kubelet config file down to disk
+	klog.V(1).Infoln("[join] writing bootstrap kubelet config file at", bootstrapKubeConfigFile)
+	if err := kubeconfigutil.WriteToDisk(bootstrapKubeConfigFile, tlsBootstrapCfg); err != nil {
+		return errors.Wrap(err, "couldn't save bootstrap-kubelet.conf to disk")
+	}
+
+	// Write the ca certificate to disk so kubelet can use it for authentication
+	cluster := tlsBootstrapCfg.Contexts[tlsBootstrapCfg.CurrentContext].Cluster
+	if _, err := os.Stat(cfg.CACertPath); os.IsNotExist(err) {
+		if err := certutil.WriteCert(cfg.CACertPath, tlsBootstrapCfg.Clusters[cluster].CertificateAuthorityData); err != nil {
+			return errors.Wrap(err, "couldn't save the CA certificate to disk")
+		}
+	}
+
+	kubeletVersion, err := preflight.GetKubeletVersion(utilsexec.New())
+	if err != nil {
+		return err
+	}
+
+	bootstrapClient, err := data.ClientSetFromFile(bootstrapKubeConfigFile)
+	if err != nil {
+		return errors.Errorf("couldn't create client from kubeconfig file %q", bootstrapKubeConfigFile)
+	}
+
+	// Configure the kubelet. In this short timeframe, kubeadm is trying to stop/restart the kubelet
+	// Try to stop the kubelet service so no race conditions occur when configuring it
+	klog.V(1).Infof("[kubelet-start] Stopping the kubelet")
+	kubeletphase.TryStopKubelet()
+
+	// Write the configuration for the kubelet (using the bootstrap token credentials) to disk so the kubelet can start
+	if err := kubeletphase.DownloadConfig(bootstrapClient, kubeletVersion, kubeadmconstants.KubeletRunDirectory); err != nil {
+		return err
+	}
+
+	// Write env file with flags for the kubelet to use. We only want to
+	// register the joining node with the specified taints if the node
+	// is not a master. The markmaster phase will register the taints otherwise.
+	registerTaintsUsingFlags := cfg.ControlPlane == nil
+	if err := kubeletphase.WriteKubeletDynamicEnvFile(&initCfg.ClusterConfiguration, &initCfg.NodeRegistration, registerTaintsUsingFlags, kubeadmconstants.KubeletRunDirectory); err != nil {
+		return err
+	}
+
+	// Try to start the kubelet service in case it's inactive
+	klog.V(1).Infof("[kubelet-start] Starting the kubelet")
+	kubeletphase.TryStartKubelet()
+
+	// Now the kubelet will perform the TLS Bootstrap, transforming /etc/kubernetes/bootstrap-kubelet.conf to /etc/kubernetes/kubelet.conf
+	// Wait for the kubelet to create the /etc/kubernetes/kubelet.conf kubeconfig file. If this process
+	// times out, display a somewhat user-friendly message.
+	waiter := apiclient.NewKubeWaiter(nil, kubeadmconstants.TLSBootstrapTimeout, os.Stdout)
+	if err := waiter.WaitForKubeletAndFunc(waitForTLSBootstrappedClient); err != nil {
+		fmt.Printf(kubeadmJoinFailMsg, err)
+		return err
+	}
+
+	// When we know the /etc/kubernetes/kubelet.conf file is available, get the client
+	client, err := data.ClientSetFromFile(kubeadmconstants.GetKubeletKubeConfigPath())
+	if err != nil {
+		return err
+	}
+
+	klog.V(1).Infof("[kubelet-start] preserving the crisocket information for the node")
+	if err := patchnodephase.AnnotateCRISocket(client, cfg.NodeRegistration.Name, cfg.NodeRegistration.CRISocket); err != nil {
+		return errors.Wrap(err, "error uploading crisocket")
+	}
+
+	return nil
+}
+
+// waitForTLSBootstrappedClient waits for the /etc/kubernetes/kubelet.conf file to be available
+func waitForTLSBootstrappedClient() error {
+	fmt.Println("[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap...")
+
+	// Loop on every falsy return. Return with an error if raised. Exit successfully if true is returned.
+	return wait.PollImmediate(kubeadmconstants.APICallRetryInterval, kubeadmconstants.TLSBootstrapTimeout, func() (bool, error) {
+		// Check that we can create a client set out of the kubelet kubeconfig. This ensures not
+		// only that the kubeconfig file exists, but that other files required by it also exist (like
+		// client certificate and key)
+		_, err := kubeconfigutil.ClientSetFromFile(kubeadmconstants.GetKubeletKubeConfigPath())
+		return (err == nil), nil
+	})
+}