Allow custom CA certificate when flag --api-server is specified (#4807)

cmd/nginx/flags.go

@@ -44,6 +44,10 @@ func parseFlags() (bool, *controller.Configuration, error) {
 Takes the form "protocol://address:port". If not specified, it is assumed the
 program runs inside a Kubernetes cluster and local discovery is attempted.`)
 
+		rootCAFile = flags.String("certificate-authority", "",
+			`Path to a cert file for the certificate authority. This certificate is used
+only when the flag --apiserver-host is specified.`)
+
 		kubeConfigFile = flags.String("kubeconfig", "",
 			`Path to a kubeconfig file containing authorization and API server information.`)
 
@@ -289,5 +293,9 @@ Takes the form "<host>:port". If not provided, no admission controller is starte
 		ValidationWebhookKeyPath:  *validationWebhookKey,
 	}
 
+	if *apiserverHost != "" {
+		config.RootCAFile = *rootCAFile
+	}
+
 	return false, config, nil
 }

cmd/nginx/main.go

@@ -36,7 +36,9 @@ import (
 	discovery "k8s.io/apimachinery/pkg/version"
 	"k8s.io/apiserver/pkg/server/healthz"
 	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/clientcmd"
+	certutil "k8s.io/client-go/util/cert"
 	"k8s.io/klog"
 
 	"k8s.io/ingress-nginx/internal/file"
@@ -69,7 +71,7 @@ func main() {
 		klog.Fatal(err)
 	}
 
-	kubeClient, err := createApiserverClient(conf.APIServerHost, conf.KubeConfigFile)
+	kubeClient, err := createApiserverClient(conf.APIServerHost, conf.RootCAFile, conf.KubeConfigFile)
 	if err != nil {
 		handleFatalInitError(err)
 	}
@@ -173,12 +175,24 @@ func handleSigterm(ngx *controller.NGINXController, exit exiter) {
 // If neither apiserverHost nor kubeConfig is passed in, we assume the
 // controller runs inside Kubernetes and fallback to the in-cluster config. If
 // the in-cluster config is missing or fails, we fallback to the default config.
-func createApiserverClient(apiserverHost, kubeConfig string) (*kubernetes.Clientset, error) {
+func createApiserverClient(apiserverHost, rootCAFile, kubeConfig string) (*kubernetes.Clientset, error) {
 	cfg, err := clientcmd.BuildConfigFromFlags(apiserverHost, kubeConfig)
 	if err != nil {
 		return nil, err
 	}
 
+	if apiserverHost != "" && rootCAFile != "" {
+		tlsClientConfig := rest.TLSClientConfig{}
+
+		if _, err := certutil.NewPool(rootCAFile); err != nil {
+			klog.Errorf("Expected to load root CA config from %s, but got err: %v", rootCAFile, err)
+		} else {
+			tlsClientConfig.CAFile = rootCAFile
+		}
+
+		cfg.TLSClientConfig = tlsClientConfig
+	}
+
 	klog.Infof("Creating API client for %s", cfg.Host)
 
 	client, err := kubernetes.NewForConfig(cfg)

cmd/nginx/main_test.go

@@ -34,7 +34,7 @@ import (
 )
 
 func TestCreateApiserverClient(t *testing.T) {
-	_, err := createApiserverClient("", "")
+	_, err := createApiserverClient("", "", "")
 	if err == nil {
 		t.Fatal("Expected an error creating REST client without an API server URL or kubeconfig file.")
 	}

internal/ingress/controller/controller.go

@@ -49,9 +49,12 @@ const (
 
 // Configuration contains all the settings required by an Ingress controller
 type Configuration struct {
-	APIServerHost  string
+	APIServerHost string
+	RootCAFile    string
+
 	KubeConfigFile string
-	Client         clientset.Interface
+
+	Client clientset.Interface
 
 	ResyncPeriod time.Duration