networking: set alloc NetworkStatus.AddressIPv6 (#23959)

when a CNI result includes an IPv6 address,
set it on the alloc's NetworkStatus for reference.

e.g.:

$ nomad alloc status -json 3dca | jq '.NetworkStatus'
{
  "Address": "172.26.64.14",
  "AddressIPv6": "fd00:a110:c8::b",
  "DNS": null,
  "InterfaceName": "eth0"
}

api/allocations.go

@@ -435,6 +435,7 @@ type AllocDeploymentStatus struct {
 type AllocNetworkStatus struct {
 	InterfaceName string
 	Address       string
+	AddressIPv6   string
 	DNS           *DNSConfig
 }
 

client/allocrunner/networking_cni.go

@@ -393,36 +393,51 @@ func (c *cniNetworkConfigurator) cniToAllocNet(res *cni.Result) (*structs.AllocN
 	}
 	sort.Strings(names)
 
-	// Use the first sandbox interface with an IP address
-	for _, name := range names {
-		iface := res.Interfaces[name]
-		if iface == nil {
+	// setStatus sets netStatus.Address and netStatus.InterfaceName
+	// if it finds a suitable interface that has IP address(es)
+	// (at least IPv4, possibly also IPv6)
+	setStatus := func(requireSandbox bool) {
+		for _, name := range names {
+			iface := res.Interfaces[name]
 			// this should never happen but this value is coming from external
 			// plugins so we should guard against it
-			delete(res.Interfaces, name)
-			continue
-		}
+			if iface == nil {
+				continue
+			}
 
-		if iface.Sandbox != "" && len(iface.IPConfigs) > 0 {
-			netStatus.Address = iface.IPConfigs[0].IP.String()
-			netStatus.InterfaceName = name
-			break
+			if requireSandbox && iface.Sandbox == "" {
+				continue
+			}
+
+			for _, ipConfig := range iface.IPConfigs {
+				isIP4 := ipConfig.IP.To4() != nil
+				if netStatus.Address == "" && isIP4 {
+					netStatus.Address = ipConfig.IP.String()
+				}
+				if netStatus.AddressIPv6 == "" && !isIP4 {
+					netStatus.AddressIPv6 = ipConfig.IP.String()
+				}
+			}
+
+			// found a good interface, so we're done
+			if netStatus.Address != "" {
+				netStatus.InterfaceName = name
+				return
+			}
 		}
 	}
 
+	// Use the first sandbox interface with an IP address
+	setStatus(true)
+
 	// If no IP address was found, use the first interface with an address
 	// found as a fallback
 	if netStatus.Address == "" {
-		for _, name := range names {
-			iface := res.Interfaces[name]
-			if len(iface.IPConfigs) > 0 {
-				ip := iface.IPConfigs[0].IP.String()
-				c.logger.Debug("no sandbox interface with an address found CNI result, using first available", "interface", name, "ip", ip)
-				netStatus.Address = ip
-				netStatus.InterfaceName = name
-				break
-			}
-		}
+		setStatus(false)
+		c.logger.Debug("no sandbox interface with an address found CNI result, using first available",
+			"interface", netStatus.InterfaceName,
+			"ip", netStatus.Address,
+		)
 	}
 
 	// If no IP address could be found, return an error

client/allocrunner/networking_cni_test.go

@@ -426,6 +426,39 @@ func TestCNI_cniToAllocNet_Invalid(t *testing.T) {
 	require.Nil(t, allocNet)
 }
 
+func TestCNI_cniToAllocNet_Dualstack(t *testing.T) {
+	ci.Parallel(t)
+
+	cniResult := &cni.Result{
+		Interfaces: map[string]*cni.Config{
+			"eth0": {
+				Sandbox: "at-the-park",
+				IPConfigs: []*cni.IPConfig{
+					{IP: net.IPv4zero}, // 0.0.0.0
+					{IP: net.IPv6zero}, // ::
+				},
+			},
+			// "a" puts this lexicographically first when sorted
+			"a-skippable-interface": {
+				// no Sandbox, so should be skipped
+				IPConfigs: []*cni.IPConfig{
+					{IP: net.IPv4(127, 3, 2, 1)},
+				},
+			},
+		},
+	}
+
+	c := &cniNetworkConfigurator{
+		logger: testlog.HCLogger(t),
+	}
+	allocNet, err := c.cniToAllocNet(cniResult)
+	must.NoError(t, err)
+	must.NotNil(t, allocNet)
+	test.Eq(t, "0.0.0.0", allocNet.Address)
+	test.Eq(t, "::", allocNet.AddressIPv6)
+	test.Eq(t, "eth0", allocNet.InterfaceName)
+}
+
 func TestCNI_addCustomCNIArgs(t *testing.T) {
 	ci.Parallel(t)
 	cniArgs := map[string]string{

nomad/structs/structs.go

@@ -12101,6 +12101,7 @@ func (s *NodeScoreMeta) Data() interface{} {
 type AllocNetworkStatus struct {
 	InterfaceName string
 	Address       string
+	AddressIPv6   string
 	DNS           *DNSConfig
 }
 
@@ -12111,6 +12112,7 @@ func (a *AllocNetworkStatus) Copy() *AllocNetworkStatus {
 	return &AllocNetworkStatus{
 		InterfaceName: a.InterfaceName,
 		Address:       a.Address,
+		AddressIPv6:   a.AddressIPv6,
 		DNS:           a.DNS.Copy(),
 	}
 }
@@ -12131,6 +12133,8 @@ func (a *AllocNetworkStatus) Equal(o *AllocNetworkStatus) bool {
 		return false
 	case a.Address != o.Address:
 		return false
+	case a.AddressIPv6 != o.AddressIPv6:
+		return false
 	case !a.DNS.Equal(o.DNS):
 		return false
 	}