Merge pull request #52188 from luxas/kubeadm_fix_join_v17

Automatic merge from submit-queue (batch tested with PRs 50949, 52155, 52175, 52112, 52188)

kubeadm: Perform TLS Bootstrapping in kubeadm join for v1.7 kubelets

**What this PR does / why we need it**:

Partially reverts 9dc3a661d7
Performs the TLS Bootstrap if `kubeadm join` v1.8 is executed on a node with a kubelet v1.7.
Since the kubelet arguments for v1.7 (from the kubeadm dropin) expects a TLS bootstrapped kubeconfig, we still have to provide this functionality in kubeadm CLI v1.8 (as we support one minor version down)

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

fixes: https://github.com/kubernetes/kubeadm/issues/429

**Special notes for your reviewer**:

This is a required bug fix for v1.8

**Release note**:

```release-note
NONE
```
@kubernetes/sig-cluster-lifecycle-pr-reviews

cmd/kubeadm/app/cmd/BUILD

@@ -29,6 +29,7 @@ go_library(
         "//cmd/kubeadm/app/discovery:go_default_library",
         "//cmd/kubeadm/app/features:go_default_library",
         "//cmd/kubeadm/app/images:go_default_library",
+        "//cmd/kubeadm/app/node:go_default_library",
         "//cmd/kubeadm/app/phases/addons/dns:go_default_library",
         "//cmd/kubeadm/app/phases/addons/proxy:go_default_library",
         "//cmd/kubeadm/app/phases/apiconfig:go_default_library",

cmd/kubeadm/app/cmd/join.go

@@ -20,7 +20,9 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"os/exec"
 	"path/filepath"
+	"strings"
 
 	"github.com/renstrom/dedent"
 	"github.com/spf13/cobra"
@@ -32,6 +34,7 @@ import (
 	"k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/validation"
 	kubeadmconstants "k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	"k8s.io/kubernetes/cmd/kubeadm/app/discovery"
+	kubeadmnode "k8s.io/kubernetes/cmd/kubeadm/app/node"
 	"k8s.io/kubernetes/cmd/kubeadm/app/preflight"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
@@ -203,7 +206,31 @@ func (j *Join) Run(out io.Writer) error {
 		return err
 	}
 
+	client, err := kubeconfigutil.KubeConfigToClientSet(cfg)
+	if err != nil {
+		return err
+	}
+	if err := kubeadmnode.ValidateAPIServer(client); err != nil {
+		return err
+	}
+
 	kubeconfigFile := filepath.Join(kubeadmconstants.KubernetesDir, kubeadmconstants.KubeletBootstrapKubeConfigFileName)
+
+	// Depending on the kubelet version, we might perform the TLS bootstrap or not
+	kubeletVersionBytes, err := exec.Command("sh", "-c", "kubelet --version").Output()
+	// In case the command executed successfully and returned v1.7-something, we'll perform TLS Bootstrapping
+	// Otherwise, just assume v1.8
+	// TODO: In the beginning of the v1.9 cycle, we can remove the logic as we then don't support v1.7 anymore
+	if err == nil && strings.HasPrefix(string(kubeletVersionBytes), "Kubernetes v1.7") {
+		hostname := nodeutil.GetHostname(j.cfg.NodeName)
+		if err := kubeadmnode.PerformTLSBootstrap(cfg, hostname); err != nil {
+			return err
+		}
+		// As we now performed the TLS Bootstrap, change the filepath to be kubelet.conf instead of bootstrap-kubelet.conf
+		kubeconfigFile = filepath.Join(kubeadmconstants.KubernetesDir, kubeadmconstants.KubeletKubeConfigFileName)
+	}
+
+	// Write the bootstrap kubelet config file or the TLS-Boostrapped kubelet config file down to disk
 	if err := kubeconfigutil.WriteToDisk(kubeconfigFile, cfg); err != nil {
 		return err
 	}

cmd/kubeadm/app/node/BUILD

@@ -8,10 +8,18 @@ load(
 
 go_library(
     name = "go_default_library",
-    srcs = ["validate.go"],
+    srcs = [
+        "csr.go",
+        "validate.go",
+    ],
     deps = [
+        "//cmd/kubeadm/app/util/kubeconfig:go_default_library",
+        "//pkg/kubelet/util/csr:go_default_library",
         "//vendor/k8s.io/api/certificates/v1beta1:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/types:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes:go_default_library",
+        "//vendor/k8s.io/client-go/tools/clientcmd/api:go_default_library",
+        "//vendor/k8s.io/client-go/util/cert:go_default_library",
     ],
 )
 

cmd/kubeadm/app/node/csr.go

@@ -0,0 +1,62 @@
+/*
+Copyright 2016 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 node
+
+import (
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/types"
+	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
+	certutil "k8s.io/client-go/util/cert"
+	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
+	"k8s.io/kubernetes/pkg/kubelet/util/csr"
+)
+
+// CSRContextAndUser defines the context to use for the client certs in the kubelet kubeconfig file
+const CSRContextAndUser = "kubelet-csr"
+
+// PerformTLSBootstrap executes a node certificate signing request.
+func PerformTLSBootstrap(cfg *clientcmdapi.Config, hostName string) error {
+	client, err := kubeconfigutil.KubeConfigToClientSet(cfg)
+	if err != nil {
+		return err
+	}
+
+	fmt.Println("[csr] Created API client to obtain unique certificate for this node, generating keys and certificate signing request")
+
+	key, err := certutil.MakeEllipticPrivateKeyPEM()
+	if err != nil {
+		return fmt.Errorf("failed to generate private key [%v]", err)
+	}
+
+	cert, err := csr.RequestNodeCertificate(client.CertificatesV1beta1().CertificateSigningRequests(), key, types.NodeName(hostName))
+	if err != nil {
+		return fmt.Errorf("failed to request signed certificate from the API server [%v]", err)
+	}
+	fmt.Println("[csr] Received signed certificate from the API server, generating KubeConfig...")
+
+	cfg.AuthInfos[CSRContextAndUser] = &clientcmdapi.AuthInfo{
+		ClientKeyData:         key,
+		ClientCertificateData: cert,
+	}
+	cfg.Contexts[CSRContextAndUser] = &clientcmdapi.Context{
+		AuthInfo: CSRContextAndUser,
+		Cluster:  cfg.Contexts[cfg.CurrentContext].Cluster,
+	}
+	cfg.CurrentContext = CSRContextAndUser
+	return nil
+}