Adds Support for Node Resource IPv6 Addressing

Adds support for the following:

1. A node resource to be assigned an IPv6 address.
2. Expands IPv4/v6 address validation checks.

Which issue this PR fixes:
fixes #44848 in combination with PR #45116

Special notes for your reviewer:

Release note:
With this PR, nodes can be assigned an IPv6 address. An IPv4 address is
preferred over an IPv6 address. IP address validation has been expanded
to check for multicast, link-local and unspecified addresses.

pkg/kubelet/kubelet_network.go

@@ -359,8 +359,13 @@ func (kl *Kubelet) GetClusterDNS(pod *v1.Pod) ([]string, []string, []string, boo
 		// local machine". A nameserver setting of localhost is equivalent to
 		// this documented behavior.
 		if kl.resolverConfig == "" {
-			hostDNS = []string{"127.0.0.1"}
 			hostSearch = []string{"."}
+			switch {
+			case kl.nodeIP == nil || kl.nodeIP.To4() != nil:
+				hostDNS = []string{"127.0.0.1"}
+			case kl.nodeIP.To16() != nil:
+				hostDNS = []string{"::1"}
+			}
 		} else {
 			hostSearch = kl.formDNSSearchForDNSDefault(hostSearch, pod)
 		}

pkg/kubelet/kubelet_network_test.go

@@ -99,28 +99,56 @@ func TestNoOpHostSupportsLegacyFeatures(t *testing.T) {
 }
 
 func TestNodeIPParam(t *testing.T) {
-	testKubelet := newTestKubelet(t, false /* controllerAttachDetachEnabled */)
+	type test struct {
-	defer testKubelet.Cleanup()
-	kubelet := testKubelet.kubelet
-	tests := []struct {
 		nodeIP   string
 		success  bool
 		testName string
-	}{
+	}
+	tests := []test{
 		{
 			nodeIP:   "",
-			success:  true,
+			success:  false,
 			testName: "IP not set",
 		},
 		{
 			nodeIP:   "127.0.0.1",
 			success:  false,
-			testName: "loopback address",
+			testName: "IPv4 loopback address",
 		},
 		{
-			nodeIP:   "FE80::0202:B3FF:FE1E:8329",
+			nodeIP:   "::1",
 			success:  false,
-			testName: "IPv6 address",
+			testName: "IPv6 loopback address",
+		},
+		{
+			nodeIP:   "224.0.0.1",
+			success:  false,
+			testName: "multicast IPv4 address",
+		},
+		{
+			nodeIP:   "ff00::1",
+			success:  false,
+			testName: "multicast IPv6 address",
+		},
+		{
+			nodeIP:   "169.254.0.1",
+			success:  false,
+			testName: "IPv4 link-local unicast address",
+		},
+		{
+			nodeIP:   "fe80::0202:b3ff:fe1e:8329",
+			success:  false,
+			testName: "IPv6 link-local unicast address",
+		},
+		{
+			nodeIP:   "0.0.0.0",
+			success:  false,
+			testName: "Unspecified IPv4 address",
+		},
+		{
+			nodeIP:   "::",
+			success:  false,
+			testName: "Unspecified IPv6 address",
 		},
 		{
 			nodeIP:   "1.2.3.4",
@@ -128,9 +156,31 @@ func TestNodeIPParam(t *testing.T) {
 			testName: "IPv4 address that doesn't belong to host",
 		},
 	}
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		assert.Error(t, err, fmt.Sprintf(
+			"Unable to obtain a list of the node's unicast interface addresses."))
+	}
+	for _, addr := range addrs {
+		var ip net.IP
+		switch v := addr.(type) {
+		case *net.IPNet:
+			ip = v.IP
+		case *net.IPAddr:
+			ip = v.IP
+		}
+		if ip.IsLoopback() || ip.IsLinkLocalUnicast() {
+			break
+		}
+		successTest := test{
+			nodeIP:   ip.String(),
+			success:  true,
+			testName: fmt.Sprintf("Success test case for address %s", ip.String()),
+		}
+		tests = append(tests, successTest)
+	}
 	for _, test := range tests {
-		kubelet.nodeIP = net.ParseIP(test.nodeIP)
+		err := validateNodeIP(net.ParseIP(test.nodeIP))
-		err := kubelet.validateNodeIP()
 		if test.success {
 			assert.NoError(t, err, "test %s", test.testName)
 		} else {

pkg/kubelet/kubelet_node_status.go

@@ -437,7 +437,7 @@ func (kl *Kubelet) recordNodeStatusEvent(eventType, event string) {
 // Set IP and hostname addresses for the node.
 func (kl *Kubelet) setNodeAddress(node *v1.Node) error {
 	if kl.nodeIP != nil {
-		if err := kl.validateNodeIP(); err != nil {
+		if err := validateNodeIP(kl.nodeIP); err != nil {
 			return fmt.Errorf("failed to validate nodeIP: %v", err)
 		}
 		glog.V(2).Infof("Using node IP: %q", kl.nodeIP.String())
@@ -503,7 +503,8 @@ func (kl *Kubelet) setNodeAddress(node *v1.Node) error {
 
 		// 1) Use nodeIP if set
 		// 2) If the user has specified an IP to HostnameOverride, use it
-		// 3) Lookup the IP from node name by DNS and use the first non-loopback ipv4 address
+		// 3) Lookup the IP from node name by DNS and use the first valid IPv4 address.
+		//    If the node does not have a valid IPv4 address, use the first valid IPv6 address.
 		// 4) Try to get the IP from the network interface used as default gateway
 		if kl.nodeIP != nil {
 			ipAddr = kl.nodeIP
@@ -511,11 +512,16 @@ func (kl *Kubelet) setNodeAddress(node *v1.Node) error {
 			ipAddr = addr
 		} else {
 			var addrs []net.IP
-			addrs, err = net.LookupIP(node.Name)
+			addrs, _ = net.LookupIP(node.Name)
 			for _, addr := range addrs {
-				if !addr.IsLoopback() && addr.To4() != nil {
+				if err = validateNodeIP(addr); err == nil {
-					ipAddr = addr
+					if addr.To4() != nil {
-					break
+						ipAddr = addr
+						break
+					}
+					if addr.To16() != nil && ipAddr == nil {
+						ipAddr = addr
+					}
 				}
 			}
 
@@ -991,17 +997,22 @@ func (kl *Kubelet) defaultNodeStatusFuncs() []func(*v1.Node) error {
 }
 
 // Validate given node IP belongs to the current host
-func (kl *Kubelet) validateNodeIP() error {
+func validateNodeIP(nodeIP net.IP) error {
-	if kl.nodeIP == nil {
-		return nil
-	}
-
 	// Honor IP limitations set in setNodeStatus()
-	if kl.nodeIP.IsLoopback() {
+	if nodeIP.To4() == nil && nodeIP.To16() == nil {
+		return fmt.Errorf("nodeIP must be a valid IP address")
+	}
+	if nodeIP.IsLoopback() {
 		return fmt.Errorf("nodeIP can't be loopback address")
 	}
-	if kl.nodeIP.To4() == nil {
+	if nodeIP.IsMulticast() {
-		return fmt.Errorf("nodeIP must be IPv4 address")
+		return fmt.Errorf("nodeIP can't be a multicast address")
+	}
+	if nodeIP.IsLinkLocalUnicast() {
+		return fmt.Errorf("nodeIP can't be a link-local unicast address")
+	}
+	if nodeIP.IsUnspecified() {
+		return fmt.Errorf("nodeIP can't be an all zeros address")
 	}
 
 	addrs, err := net.InterfaceAddrs()
@@ -1016,9 +1027,9 @@ func (kl *Kubelet) validateNodeIP() error {
 		case *net.IPAddr:
 			ip = v.IP
 		}
-		if ip != nil && ip.Equal(kl.nodeIP) {
+		if ip != nil && ip.Equal(nodeIP) {
 			return nil
 		}
 	}
-	return fmt.Errorf("Node IP: %q not found in the host's network interfaces", kl.nodeIP.String())
+	return fmt.Errorf("Node IP: %q not found in the host's network interfaces", nodeIP.String())
 }

pkg/kubelet/kubelet_node_status_test.go

@@ -144,7 +144,7 @@ func TestNodeStatusWithCloudProviderNodeIP(t *testing.T) {
 		Spec:       v1.NodeSpec{},
 	}
 
-	// TODO : is it possible to mock kubelet.validateNodeIP() to avoid relying on the host interface addresses ?
+	// TODO : is it possible to mock validateNodeIP() to avoid relying on the host interface addresses ?
 	addrs, err := net.InterfaceAddrs()
 	assert.NoError(t, err)
 	for _, addr := range addrs {