kube-apiserver: disallow --secure-port 0

cmd/kube-apiserver/app/options/options_test.go

@@ -166,6 +166,7 @@ func TestAddFlags(t *testing.T) {
 				PairName:      "apiserver",
 			},
 			HTTP2MaxStreamsPerConnection: 42,
+			Required:                     true,
 		}),
 		InsecureServing: &kubeoptions.InsecureServingOptions{
 			BindAddress: net.ParseIP("127.0.0.1"),

pkg/kubeapiserver/options/serving.go

@@ -36,6 +36,7 @@ func NewSecureServingOptions() *genericoptions.SecureServingOptionsWithLoopback
 	return genericoptions.WithLoopback(&genericoptions.SecureServingOptions{
 		BindAddress: net.ParseIP("0.0.0.0"),
 		BindPort:    6443,
+		Required:    true,
 		ServerCert: genericoptions.GeneratableKeyCert{
 			PairName:      "apiserver",
 			CertDirectory: "/var/run/kubernetes",

staging/src/k8s.io/apiserver/pkg/server/options/serving.go

@@ -40,6 +40,8 @@ type SecureServingOptions struct {
 	// BindNetwork is the type of network to bind to - defaults to "tcp", accepts "tcp",
 	// "tcp4", and "tcp6".
 	BindNetwork string
+	// Required set to true means that BindPort cannot be zero.
+	Required bool
 
 	// Listener is the secure server network listener.
 	// either Listener or BindAddress/BindPort/BindNetwork is set,
@@ -102,7 +104,9 @@ func (s *SecureServingOptions) Validate() []error {
 
 	errors := []error{}
 
-	if s.BindPort < 0 || s.BindPort > 65535 {
+	if s.Required && s.BindPort < 1 || s.BindPort > 65535 {
+		errors = append(errors, fmt.Errorf("--secure-port %v must be between 1 and 65535, inclusive. It cannot turned off with 0", s.BindPort))
+	} else if s.BindPort < 0 || s.BindPort > 65535 {
 		errors = append(errors, fmt.Errorf("--secure-port %v must be between 0 and 65535, inclusive. 0 for turning off secure port", s.BindPort))
 	}
 
@@ -118,9 +122,14 @@ func (s *SecureServingOptions) AddFlags(fs *pflag.FlagSet) {
 		"The IP address on which to listen for the --secure-port port. The "+
 		"associated interface(s) must be reachable by the rest of the cluster, and by CLI/web "+
 		"clients. If blank, all interfaces will be used (0.0.0.0 for all IPv4 interfaces and :: for all IPv6 interfaces).")
-	fs.IntVar(&s.BindPort, "secure-port", s.BindPort, ""+
-		"The port on which to serve HTTPS with authentication and authorization. If 0, "+
-		"don't serve HTTPS at all.")
+
+	desc := "The port on which to serve HTTPS with authentication and authorization."
+	if s.Required {
+		desc += "It cannot switched off with 0."
+	} else {
+		desc += "If 0, don't serve HTTPS at all."
+	}
+	fs.IntVar(&s.BindPort, "secure-port", s.BindPort, desc)
 
 	fs.StringVar(&s.ServerCert.CertDirectory, "cert-dir", s.ServerCert.CertDirectory, ""+
 		"The directory where the TLS certs are located. "+