Merge pull request #30922 from yifan-gu/tls_bootstrap_refactor

Automatic merge from submit-queue

Implement TLS bootstrap for kubelet using `--experimental-bootstrap-kubeconfig`  (2nd take)

Ref kubernetes/features#43 (comment)

cc @gtank @philips @mikedanese @aaronlevy @liggitt @deads2k @errordeveloper @justinsb 


Continue on the older PR https://github.com/kubernetes/kubernetes/pull/30094 as there are too many comments on that one and it's not loadable now.

cmd/kubelet/app/bootstrap.go

@@ -0,0 +1,259 @@
+/*
+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 app
+
+import (
+	"crypto/x509/pkix"
+	"fmt"
+	"io/ioutil"
+	_ "net/http/pprof"
+	"os"
+	"path/filepath"
+
+	"github.com/golang/glog"
+
+	"k8s.io/kubernetes/pkg/api"
+	"k8s.io/kubernetes/pkg/api/unversioned"
+	"k8s.io/kubernetes/pkg/apis/certificates"
+	unversionedcertificates "k8s.io/kubernetes/pkg/client/clientset_generated/internalclientset/typed/certificates/unversioned"
+	"k8s.io/kubernetes/pkg/client/restclient"
+	"k8s.io/kubernetes/pkg/client/unversioned/clientcmd"
+	clientcmdapi "k8s.io/kubernetes/pkg/client/unversioned/clientcmd/api"
+	"k8s.io/kubernetes/pkg/fields"
+	utilcertificates "k8s.io/kubernetes/pkg/util/certificates"
+	"k8s.io/kubernetes/pkg/util/crypto"
+	"k8s.io/kubernetes/pkg/watch"
+)
+
+const (
+	defaultKubeletClientCertificateFile = "kubelet-client.crt"
+	defaultKubeletClientKeyFile         = "kubelet-client.key"
+)
+
+// bootstrapClientCert requests a client cert for kubelet if the kubeconfigPath file does not exist.
+// The kubeconfig at bootstrapPath is used to request a client certificate from the API server.
+// On success, a kubeconfig file referencing the generated key and obtained certificate is written to kubeconfigPath.
+// The certificate and key file are stored in certDir.
+func bootstrapClientCert(kubeconfigPath string, bootstrapPath string, certDir string, nodeName string) error {
+	// Short-circuit if the kubeconfig file already exists.
+	// TODO: inspect the kubeconfig, ensure a rest client can be built from it, verify client cert expiration, etc.
+	_, err := os.Stat(kubeconfigPath)
+	if err == nil {
+		glog.V(2).Infof("Kubeconfig %s exists, skipping bootstrap", kubeconfigPath)
+		return nil
+	}
+	if !os.IsNotExist(err) {
+		glog.Errorf("Error reading kubeconfig %s, skipping bootstrap: %v", kubeconfigPath, err)
+		return err
+	}
+
+	glog.V(2).Info("Using bootstrap kubeconfig to generate TLS client cert, key and kubeconfig file")
+
+	bootstrapClientConfig, err := loadRESTClientConfig(bootstrapPath)
+	if err != nil {
+		return fmt.Errorf("unable to load bootstrap kubeconfig: %v", err)
+	}
+	bootstrapClient, err := unversionedcertificates.NewForConfig(bootstrapClientConfig)
+	if err != nil {
+		return fmt.Errorf("unable to create certificates signing request client: %v", err)
+	}
+
+	success := false
+
+	// Get the private key.
+	keyPath, err := filepath.Abs(filepath.Join(certDir, defaultKubeletClientKeyFile))
+	if err != nil {
+		return fmt.Errorf("unable to build bootstrap key path: %v", err)
+	}
+	keyData, generatedKeyFile, err := loadOrGenerateKeyFile(keyPath)
+	if err != nil {
+		return err
+	}
+	if generatedKeyFile {
+		defer func() {
+			if !success {
+				if err := os.Remove(keyPath); err != nil {
+					glog.Warningf("Cannot clean up the key file %q: %v", keyPath, err)
+				}
+			}
+		}()
+	}
+
+	// Get the cert.
+	certPath, err := filepath.Abs(filepath.Join(certDir, defaultKubeletClientCertificateFile))
+	if err != nil {
+		return fmt.Errorf("unable to build bootstrap client cert path: %v", err)
+	}
+	certData, err := RequestClientCertificate(bootstrapClient.CertificateSigningRequests(), keyData, nodeName)
+	if err != nil {
+		return err
+	}
+	if err := crypto.WriteCertToPath(certPath, certData); err != nil {
+		return err
+	}
+	defer func() {
+		if !success {
+			if err := os.Remove(certPath); err != nil {
+				glog.Warningf("Cannot clean up the cert file %q: %v", certPath, err)
+			}
+		}
+	}()
+
+	// Get the CA data from the bootstrap client config.
+	caFile, caData := bootstrapClientConfig.CAFile, []byte{}
+	if len(caFile) == 0 {
+		caData = bootstrapClientConfig.CAData
+	}
+
+	// Build resulting kubeconfig.
+	kubeconfigData := clientcmdapi.Config{
+		// Define a cluster stanza based on the bootstrap kubeconfig.
+		Clusters: map[string]*clientcmdapi.Cluster{"default-cluster": {
+			Server:                   bootstrapClientConfig.Host,
+			InsecureSkipTLSVerify:    bootstrapClientConfig.Insecure,
+			CertificateAuthority:     caFile,
+			CertificateAuthorityData: caData,
+		}},
+		// Define auth based on the obtained client cert.
+		AuthInfos: map[string]*clientcmdapi.AuthInfo{"default-auth": {
+			ClientCertificate: certPath,
+			ClientKey:         keyPath,
+		}},
+		// Define a context that connects the auth info and cluster, and set it as the default
+		Contexts: map[string]*clientcmdapi.Context{"default-context": {
+			Cluster:   "default-cluster",
+			AuthInfo:  "default-auth",
+			Namespace: "default",
+		}},
+		CurrentContext: "default-context",
+	}
+
+	// Marshal to disk
+	if err := clientcmd.WriteToFile(kubeconfigData, kubeconfigPath); err != nil {
+		return err
+	}
+
+	success = true
+	return nil
+}
+
+func loadRESTClientConfig(kubeconfig string) (*restclient.Config, error) {
+	// Load structured kubeconfig data from the given path.
+	loader := &clientcmd.ClientConfigLoadingRules{ExplicitPath: kubeconfig}
+	loadedConfig, err := loader.Load()
+	if err != nil {
+		return nil, err
+	}
+	// Flatten the loaded data to a particular restclient.Config based on the current context.
+	return clientcmd.NewNonInteractiveClientConfig(
+		*loadedConfig,
+		loadedConfig.CurrentContext,
+		&clientcmd.ConfigOverrides{},
+		loader,
+	).ClientConfig()
+}
+
+func loadOrGenerateKeyFile(keyPath string) (data []byte, wasGenerated bool, err error) {
+	loadedData, err := ioutil.ReadFile(keyPath)
+	if err == nil {
+		return loadedData, false, err
+	}
+	if !os.IsNotExist(err) {
+		return nil, false, fmt.Errorf("error loading key from %s: %v", keyPath, err)
+	}
+
+	generatedData, err := utilcertificates.GeneratePrivateKey()
+	if err != nil {
+		return nil, false, fmt.Errorf("error generating key: %v", err)
+	}
+	if err := crypto.WriteKeyToPath(keyPath, generatedData); err != nil {
+		return nil, false, fmt.Errorf("error writing key to %s: %v", keyPath, err)
+	}
+	return generatedData, true, nil
+}
+
+// RequestClientCertificate will create a certificate signing request and send it to API server,
+// then it will watch the object's status, once approved by API server, it will return the API
+// server's issued certificate (pem-encoded). If there is any errors, or the watch timeouts,
+// it will return an error.
+func RequestClientCertificate(client unversionedcertificates.CertificateSigningRequestInterface, privateKeyData []byte, nodeName string) (certData []byte, err error) {
+	subject := &pkix.Name{
+		Organization: []string{"system:nodes"},
+		CommonName:   fmt.Sprintf("system:node:%s", nodeName),
+	}
+
+	privateKey, err := utilcertificates.ParsePrivateKey(privateKeyData)
+	if err != nil {
+		return nil, fmt.Errorf("invalid private key for certificate request: %v", err)
+	}
+	csr, err := utilcertificates.NewCertificateRequest(privateKey, subject, nil, nil)
+	if err != nil {
+		return nil, fmt.Errorf("unable to generate certificate request: %v", err)
+	}
+
+	req, err := client.Create(&certificates.CertificateSigningRequest{
+		// Username, UID, Groups will be injected by API server.
+		TypeMeta:   unversioned.TypeMeta{Kind: "CertificateSigningRequest"},
+		ObjectMeta: api.ObjectMeta{GenerateName: "csr-"},
+
+		// TODO: For now, this is a request for a certificate with allowed usage of "TLS Web Client Authentication".
+		// Need to figure out whether/how to surface the allowed usage in the spec.
+		Spec: certificates.CertificateSigningRequestSpec{Request: csr},
+	})
+	if err != nil {
+		return nil, fmt.Errorf("cannot create certificate signing request: %v", err)
+
+	}
+
+	// Make a default timeout = 3600s.
+	var defaultTimeoutSeconds int64 = 3600
+	resultCh, err := client.Watch(api.ListOptions{
+		Watch:          true,
+		TimeoutSeconds: &defaultTimeoutSeconds,
+		FieldSelector:  fields.OneTermEqualSelector("metadata.name", req.Name),
+	})
+	if err != nil {
+		return nil, fmt.Errorf("cannot watch on the certificate signing request: %v", err)
+	}
+
+	var status certificates.CertificateSigningRequestStatus
+	ch := resultCh.ResultChan()
+
+	for {
+		event, ok := <-ch
+		if !ok {
+			break
+		}
+
+		if event.Type == watch.Modified || event.Type == watch.Added {
+			if event.Object.(*certificates.CertificateSigningRequest).UID != req.UID {
+				continue
+			}
+			status = event.Object.(*certificates.CertificateSigningRequest).Status
+			for _, c := range status.Conditions {
+				if c.Type == certificates.CertificateDenied {
+					return nil, fmt.Errorf("certificate signing request is not approved, reason: %v, message: %v", c.Reason, c.Message)
+				}
+				if c.Type == certificates.CertificateApproved && status.Certificate != nil {
+					return status.Certificate, nil
+				}
+			}
+		}
+	}
+
+	return nil, fmt.Errorf("watch channel closed")
+}

cmd/kubelet/app/bootstrap_test.go

@@ -0,0 +1,85 @@
+/*
+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 app
+
+import (
+	"io/ioutil"
+	"os"
+	"reflect"
+	"testing"
+
+	"k8s.io/kubernetes/pkg/client/restclient"
+	"k8s.io/kubernetes/pkg/util/diff"
+)
+
+func TestLoadRESTClientConfig(t *testing.T) {
+	testData := []byte(`
+apiVersion: v1
+kind: Config
+clusters:
+- cluster:
+    certificate-authority: ca-a.crt
+    server: https://cluster-a.com
+  name: cluster-a
+- cluster:
+    certificate-authority-data: VGVzdA== 
+    server: https://cluster-b.com
+  name: cluster-b
+contexts:
+- context:
+    cluster: cluster-a
+    namespace: ns-a
+    user: user-a
+  name: context-a
+- context:
+    cluster: cluster-b
+    namespace: ns-b
+    user: user-b
+  name: context-b
+current-context: context-b
+users:
+- name: user-a
+  user:
+    token: mytoken-a
+- name: user-b
+  user:
+    token: mytoken-b
+`)
+	f, err := ioutil.TempFile("", "kubeconfig")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(f.Name())
+	ioutil.WriteFile(f.Name(), testData, os.FileMode(0755))
+
+	config, err := loadRESTClientConfig(f.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectedConfig := &restclient.Config{
+		Host: "https://cluster-b.com",
+		TLSClientConfig: restclient.TLSClientConfig{
+			CAData: []byte(`Test`),
+		},
+		BearerToken: "mytoken-b",
+	}
+
+	if !reflect.DeepEqual(config, expectedConfig) {
+		t.Errorf("Unexpected config: %s", diff.ObjectDiff(config, expectedConfig))
+	}
+}

cmd/kubelet/app/options/options.go

@@ -41,7 +41,9 @@ const (
 type KubeletServer struct {
 	componentconfig.KubeletConfiguration
 
-	KubeConfig util.StringFlag
+	KubeConfig          util.StringFlag
+	BootstrapKubeconfig string
+
 	// If true, an invalid KubeConfig will result in the Kubelet exiting with an error.
 	RequireKubeConfig bool
 	AuthPath          util.StringFlag // Deprecated -- use KubeConfig instead
@@ -97,6 +99,10 @@ func (s *KubeletServer) AddFlags(fs *pflag.FlagSet) {
 	fs.StringVar(&s.TLSPrivateKeyFile, "tls-private-key-file", s.TLSPrivateKeyFile, "File containing x509 private key matching --tls-cert-file.")
 	fs.StringVar(&s.CertDirectory, "cert-dir", s.CertDirectory, "The directory where the TLS certs are located (by default /var/run/kubernetes). "+
 		"If --tls-cert-file and --tls-private-key-file are provided, this flag will be ignored.")
+	fs.StringVar(&s.BootstrapKubeconfig, "experimental-bootstrap-kubeconfig", s.BootstrapKubeconfig, "<Warning: Experimental feature> Path to a kubeconfig file that will be used to get client certificate for kubelet. "+
+		"If the file specified by --kubeconfig does not exist, the bootstrap kubeconfig is used to request a client certificate from the API server. "+
+		"On success, a kubeconfig file referencing the generated key and obtained certificate is written to the path specified by --kubeconfig. "+
+		"The certificate and key file will be stored in the directory pointed by --cert-dir.")
 	fs.StringVar(&s.HostnameOverride, "hostname-override", s.HostnameOverride, "If non-empty, will use this string as identification instead of the actual hostname.")
 	fs.StringVar(&s.PodInfraContainerImage, "pod-infra-container-image", s.PodInfraContainerImage, "The image whose network/ipc namespaces containers in each pod will use.")
 	fs.StringVar(&s.DockerEndpoint, "docker-endpoint", s.DockerEndpoint, "Use this for the docker endpoint to communicate with")

cmd/kubelet/app/server.go

@@ -350,6 +350,33 @@ func run(s *options.KubeletServer, kcfg *KubeletConfig) (err error) {
 
 	if kcfg == nil {
 		var kubeClient, eventClient *clientset.Clientset
+		var autoDetectCloudProvider bool
+		var cloud cloudprovider.Interface
+
+		if s.CloudProvider == kubeExternal.AutoDetectCloudProvider {
+			autoDetectCloudProvider = true
+		} else {
+			cloud, err = cloudprovider.InitCloudProvider(s.CloudProvider, s.CloudConfigFile)
+			if err != nil {
+				return err
+			}
+			if cloud == nil {
+				glog.V(2).Infof("No cloud provider specified: %q from the config file: %q\n", s.CloudProvider, s.CloudConfigFile)
+			} else {
+				glog.V(2).Infof("Successfully initialized cloud provider: %q from the config file: %q\n", s.CloudProvider, s.CloudConfigFile)
+			}
+		}
+
+		if s.BootstrapKubeconfig != "" {
+			nodeName, err := getNodeName(cloud, nodeutil.GetHostname(s.HostnameOverride))
+			if err != nil {
+				return err
+			}
+			if err := bootstrapClientCert(s.KubeConfig.Value(), s.BootstrapKubeconfig, s.CertDirectory, nodeName); err != nil {
+				return err
+			}
+		}
+
 		clientConfig, err := CreateAPIServerClientConfig(s)
 		if err == nil {
 			kubeClient, err = clientset.NewForConfig(clientConfig)
@@ -374,24 +401,12 @@ func run(s *options.KubeletServer, kcfg *KubeletConfig) (err error) {
 		if err != nil {
 			return err
 		}
+
 		kcfg = cfg
+		kcfg.AutoDetectCloudProvider = autoDetectCloudProvider
+		kcfg.Cloud = cloud
 		kcfg.KubeClient = kubeClient
 		kcfg.EventClient = eventClient
-
-		if s.CloudProvider == kubeExternal.AutoDetectCloudProvider {
-			kcfg.AutoDetectCloudProvider = true
-		} else {
-			cloud, err := cloudprovider.InitCloudProvider(s.CloudProvider, s.CloudConfigFile)
-			if err != nil {
-				return err
-			}
-			if cloud == nil {
-				glog.V(2).Infof("No cloud provider specified: %q from the config file: %q\n", s.CloudProvider, s.CloudConfigFile)
-			} else {
-				glog.V(2).Infof("Successfully initialized cloud provider: %q from the config file: %q\n", s.CloudProvider, s.CloudConfigFile)
-				kcfg.Cloud = cloud
-			}
-		}
 	}
 
 	if kcfg.CAdvisorInterface == nil {
@@ -454,13 +469,35 @@ func run(s *options.KubeletServer, kcfg *KubeletConfig) (err error) {
 	return nil
 }
 
+// getNodeName returns the node name according to the cloud provider
+// if cloud provider is specified. Otherwise, returns the hostname of the node.
+func getNodeName(cloud cloudprovider.Interface, hostname string) (string, error) {
+	if cloud == nil {
+		return hostname, nil
+	}
+
+	instances, ok := cloud.Instances()
+	if !ok {
+		return "", fmt.Errorf("failed to get instances from cloud provider")
+	}
+
+	nodeName, err := instances.CurrentNodeName(hostname)
+	if err != nil {
+		return "", fmt.Errorf("error fetching current instance name from cloud provider: %v", err)
+	}
+
+	glog.V(2).Infof("cloud provider determined current node name to be %s", nodeName)
+
+	return nodeName, nil
+}
+
 // InitializeTLS checks for a configured TLSCertFile and TLSPrivateKeyFile: if unspecified a new self-signed
 // certificate and key file are generated. Returns a configured server.TLSOptions object.
 func InitializeTLS(s *options.KubeletServer) (*server.TLSOptions, error) {
 	if s.TLSCertFile == "" && s.TLSPrivateKeyFile == "" {
 		s.TLSCertFile = path.Join(s.CertDirectory, "kubelet.crt")
 		s.TLSPrivateKeyFile = path.Join(s.CertDirectory, "kubelet.key")
-		if crypto.ShouldGenSelfSignedCerts(s.TLSCertFile, s.TLSPrivateKeyFile) {
+		if !crypto.FoundCertOrKey(s.TLSCertFile, s.TLSPrivateKeyFile) {
 			if err := crypto.GenerateSelfSignedCert(nodeutil.GetHostname(s.HostnameOverride), s.TLSCertFile, s.TLSPrivateKeyFile, nil, nil); err != nil {
 				return nil, fmt.Errorf("unable to generate self signed cert: %v", err)
 			}
@@ -693,23 +730,10 @@ func RunKubelet(kcfg *KubeletConfig) error {
 	kcfg.Hostname = nodeutil.GetHostname(kcfg.HostnameOverride)
 
 	if len(kcfg.NodeName) == 0 {
-		// Query the cloud provider for our node name, default to Hostname
-		nodeName := kcfg.Hostname
-		if kcfg.Cloud != nil {
-			var err error
-			instances, ok := kcfg.Cloud.Instances()
-			if !ok {
-				return fmt.Errorf("failed to get instances from cloud provider")
-			}
-
-			nodeName, err = instances.CurrentNodeName(kcfg.Hostname)
-			if err != nil {
-				return fmt.Errorf("error fetching current instance name from cloud provider: %v", err)
-			}
-
-			glog.V(2).Infof("cloud provider determined current node name to be %s", nodeName)
+		nodeName, err := getNodeName(kcfg.Cloud, kcfg.Hostname)
+		if err != nil {
+			return err
 		}
-
 		kcfg.NodeName = nodeName
 	}
 

hack/verify-flags/known-flags.txt

@@ -163,6 +163,7 @@ executor-logv
 executor-path
 executor-suicide-timeout
 exit-on-lock-contention
+experimental-bootstrap-kubeconfig
 experimental-flannel-overlay
 experimental-keystone-url
 experimental-nvidia-gpus

pkg/genericapiserver/genericapiserver.go

@@ -723,7 +723,7 @@ func (s *GenericAPIServer) Run(options *options.ServerRunOptions) {
 			alternateDNS := []string{"kubernetes.default.svc", "kubernetes.default", "kubernetes"}
 			// It would be nice to set a fqdn subject alt name, but only the kubelets know, the apiserver is clueless
 			// alternateDNS = append(alternateDNS, "kubernetes.default.svc.CLUSTER.DNS.NAME")
-			if crypto.ShouldGenSelfSignedCerts(options.TLSCertFile, options.TLSPrivateKeyFile) {
+			if !crypto.FoundCertOrKey(options.TLSCertFile, options.TLSPrivateKeyFile) {
 				if err := crypto.GenerateSelfSignedCert(s.ClusterIP.String(), options.TLSCertFile, options.TLSPrivateKeyFile, alternateIPs, alternateDNS); err != nil {
 					glog.Errorf("Unable to generate self signed cert: %v", err)
 				} else {

pkg/util/certificates/csr.go

@@ -17,9 +17,16 @@ limitations under the License.
 package certificates
 
 import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	cryptorand "crypto/rand"
+	"crypto/rsa"
 	"crypto/x509"
+	"crypto/x509/pkix"
 	"encoding/pem"
 	"errors"
+	"fmt"
+	"net"
 
 	"k8s.io/kubernetes/pkg/apis/certificates"
 )
@@ -38,3 +45,94 @@ func ParseCertificateRequestObject(obj *certificates.CertificateSigningRequest)
 	}
 	return csr, nil
 }
+
+// GeneratePrivateKey returns PEM data containing a generated ECDSA private key
+func GeneratePrivateKey() ([]byte, error) {
+	privateKey, err := ecdsa.GenerateKey(elliptic.P256(), cryptorand.Reader)
+	if err != nil {
+		return nil, err
+	}
+
+	derBytes, err := x509.MarshalECPrivateKey(privateKey)
+	if err != nil {
+		return nil, err
+	}
+
+	privateKeyPemBlock := &pem.Block{
+		Type:  "EC PRIVATE KEY",
+		Bytes: derBytes,
+	}
+	return pem.EncodeToMemory(privateKeyPemBlock), nil
+}
+
+// ParsePrivateKey returns a private key parsed from a PEM block in the supplied data.
+// Recognizes PEM blocks for "EC PRIVATE KEY" and "RSA PRIVATE KEY"
+func ParsePrivateKey(keyData []byte) (interface{}, error) {
+	for {
+		var privateKeyPemBlock *pem.Block
+		privateKeyPemBlock, keyData = pem.Decode(keyData)
+		if privateKeyPemBlock == nil {
+			// we read all the PEM blocks and didn't recognize one
+			return nil, fmt.Errorf("no private key PEM block found")
+		}
+
+		switch privateKeyPemBlock.Type {
+		case "EC PRIVATE KEY":
+			return x509.ParseECPrivateKey(privateKeyPemBlock.Bytes)
+		case "RSA PRIVATE KEY":
+			return x509.ParsePKCS1PrivateKey(privateKeyPemBlock.Bytes)
+		}
+	}
+}
+
+// NewCertificateRequest generates a PEM-encoded CSR using the supplied private key, subject, and SANs.
+// privateKey must be a *ecdsa.PrivateKey or *rsa.PrivateKey.
+func NewCertificateRequest(privateKey interface{}, subject *pkix.Name, dnsSANs []string, ipSANs []net.IP) (csr []byte, err error) {
+	var sigType x509.SignatureAlgorithm
+
+	switch privateKey := privateKey.(type) {
+	case *ecdsa.PrivateKey:
+		switch privateKey.Curve {
+		case elliptic.P224(), elliptic.P256():
+			sigType = x509.ECDSAWithSHA256
+		case elliptic.P384():
+			sigType = x509.ECDSAWithSHA384
+		case elliptic.P521():
+			sigType = x509.ECDSAWithSHA512
+		default:
+			return nil, fmt.Errorf("unknown elliptic curve: %v", privateKey.Curve)
+		}
+	case *rsa.PrivateKey:
+		keySize := privateKey.N.BitLen()
+		switch {
+		case keySize >= 4096:
+			sigType = x509.SHA512WithRSA
+		case keySize >= 3072:
+			sigType = x509.SHA384WithRSA
+		default:
+			sigType = x509.SHA256WithRSA
+		}
+
+	default:
+		return nil, fmt.Errorf("unsupported key type: %T", privateKey)
+	}
+
+	template := &x509.CertificateRequest{
+		Subject:            *subject,
+		SignatureAlgorithm: sigType,
+		DNSNames:           dnsSANs,
+		IPAddresses:        ipSANs,
+	}
+
+	csr, err = x509.CreateCertificateRequest(cryptorand.Reader, template, privateKey)
+	if err != nil {
+		return nil, err
+	}
+
+	csrPemBlock := &pem.Block{
+		Type:  "CERTIFICATE REQUEST",
+		Bytes: csr,
+	}
+
+	return pem.EncodeToMemory(csrPemBlock), nil
+}

pkg/util/certificates/csr_test.go

@@ -0,0 +1,46 @@
+/*
+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 certificates
+
+import (
+	"crypto/x509/pkix"
+	"io/ioutil"
+	"net"
+	"testing"
+)
+
+func TestNewCertificateRequest(t *testing.T) {
+	keyFile := "testdata/dontUseThisKey.pem"
+	subject := &pkix.Name{
+		CommonName: "kube-worker",
+	}
+	dnsSANs := []string{"localhost"}
+	ipSANs := []net.IP{net.ParseIP("127.0.0.1")}
+
+	keyData, err := ioutil.ReadFile(keyFile)
+	if err != nil {
+		t.Fatal(err)
+	}
+	key, err := ParsePrivateKey(keyData)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = NewCertificateRequest(key, subject, dnsSANs, ipSANs)
+	if err != nil {
+		t.Error(err)
+	}
+}

pkg/util/certificates/testdata/dontUseThisKey.pem

@@ -0,0 +1,6 @@
+-----BEGIN EC PRIVATE KEY-----
+MIGkAgEBBDAPEbSXwyDfWf0+61Oofd7aHkmdX69mrzD2Xb1CHF5syfsoRIhnG0dJ
+ozBulPZCDDWgBwYFK4EEACKhZANiAATjlMJAtKhEPqU/i7MsrgKcK/RmXHC6He7W
+0p69+9qFXg2raJ9zvvbKxkiu2ELOYRDAz0utcFTBOIgoUJEzBVmsjZQ7dvFa1BKP
+Ym7MFAKG3O2espBqXn+audgdHGh5B0I=
+-----END EC PRIVATE KEY-----

pkg/util/crypto/crypto.go

@@ -33,14 +33,14 @@ import (
 	"time"
 )
 
-// ShouldGenSelfSignedCerts returns false if the certificate or key files already exists,
-// otherwise returns true.
-func ShouldGenSelfSignedCerts(certPath, keyPath string) bool {
+// FoundCertOrKey returns true if the certificate or key files already exists,
+// otherwise returns false.
+func FoundCertOrKey(certPath, keyPath string) bool {
 	if canReadFile(certPath) || canReadFile(keyPath) {
-		return false
+		return true
 	}
 
-	return true
+	return false
 }
 
 // If the file represented by path exists and
@@ -109,24 +109,46 @@ func GenerateSelfSignedCert(host, certPath, keyPath string, alternateIPs []net.I
 	}
 
 	// Write cert
-	if err := os.MkdirAll(filepath.Dir(certPath), os.FileMode(0755)); err != nil {
-		return err
-	}
-	if err := ioutil.WriteFile(certPath, certBuffer.Bytes(), os.FileMode(0644)); err != nil {
+	if err := WriteCertToPath(certPath, certBuffer.Bytes()); err != nil {
 		return err
 	}
 
 	// Write key
-	if err := os.MkdirAll(filepath.Dir(keyPath), os.FileMode(0755)); err != nil {
-		return err
-	}
-	if err := ioutil.WriteFile(keyPath, keyBuffer.Bytes(), os.FileMode(0600)); err != nil {
+	if err := WriteKeyToPath(keyPath, keyBuffer.Bytes()); err != nil {
 		return err
 	}
 
 	return nil
 }
 
+// WriteCertToPath writes the pem-encoded certificate data to certPath.
+// The certificate file will be created with file mode 0644.
+// If the certificate file already exists, it will be overwritten.
+// The parent directory of the certPath will be created as needed with file mode 0755.
+func WriteCertToPath(certPath string, data []byte) error {
+	if err := os.MkdirAll(filepath.Dir(certPath), os.FileMode(0755)); err != nil {
+		return err
+	}
+	if err := ioutil.WriteFile(certPath, data, os.FileMode(0644)); err != nil {
+		return err
+	}
+	return nil
+}
+
+// WriteKeyToPath writes the pem-encoded key data to keyPath.
+// The key file will be created with file mode 0600.
+// If the key file already exists, it will be overwritten.
+// The parent directory of the keyPath will be created as needed with file mode 0755.
+func WriteKeyToPath(keyPath string, data []byte) error {
+	if err := os.MkdirAll(filepath.Dir(keyPath), os.FileMode(0755)); err != nil {
+		return err
+	}
+	if err := ioutil.WriteFile(keyPath, data, os.FileMode(0600)); err != nil {
+		return err
+	}
+	return nil
+}
+
 // CertPoolFromFile returns an x509.CertPool containing the certificates in the given PEM-encoded file.
 // Returns an error if the file could not be read, a certificate could not be parsed, or if the file does not contain any certificates
 func CertPoolFromFile(filename string) (*x509.CertPool, error) {