Auto select network iface when not provided (#1579)

Author: marccampbell

cmd/installer/cli/install2.go

@@ -31,14 +31,17 @@ type Install2CmdFlags struct {
 	dataDir                 string
 	licenseFile             string
 	localArtifactMirrorPort int
-	networkInterface        string
 	assumeYes               bool
 	overrides               string
 	privateCAs              []string
 	skipHostPreflights      bool
 	ignoreHostPreflights    bool
 	configValues            string
 
+	networkInterface               string
+	isAutoSelectedNetworkInterface bool
+	autoSelectNetworkInterfaceErr  error
+
 	license *kotsv1beta1.License
 	proxy   *ecv1beta1.ProxySpec
 
@@ -88,6 +91,17 @@ func Install2Cmd(ctx context.Context, name string) *cobra.Command {
 			flags.podCIDR = pod
 			flags.serviceCIDR = svc
 
+			// if a network interface flag was not provided, attempt to discover it
+			if flags.networkInterface == "" {
+				autoInterface, err := determineBestNetworkInterface()
+				if err != nil {
+					flags.autoSelectNetworkInterfaceErr = err
+				} else {
+					flags.isAutoSelectedNetworkInterface = true
+					flags.networkInterface = autoInterface
+				}
+			}
+
 			// validate the the license is indeed a license file
 			l, err := helpers.ParseLicense(flags.licenseFile)
 			if err != nil {

cmd/installer/cli/network_interface.go

@@ -0,0 +1,64 @@
+package cli
+
+import (
+	"fmt"
+	"net"
+
+	apimachinerynet "k8s.io/apimachinery/pkg/util/net"
+)
+
+var (
+	ErrNoAutoInterface              = fmt.Errorf("no auto interface found")
+	ErrBestInterfaceWas6            = fmt.Errorf("best interface was IPv6")
+	ErrCannotDetermineInterfaceName = fmt.Errorf("cannot determine interface name")
+)
+
+// determineBestNetworkInterface attempts to determine the best network interface to use for the cluster.
+func determineBestNetworkInterface() (string, error) {
+	iface, err := apimachinerynet.ChooseHostInterface()
+
+	if err != nil || iface == nil {
+		return "", ErrNoAutoInterface
+	}
+
+	if iface.To4() == nil {
+		return "", ErrBestInterfaceWas6
+	}
+
+	ifaceName, err := findInterfaceNameByIP(iface)
+	if err != nil {
+		return "", ErrCannotDetermineInterfaceName
+	}
+
+	return ifaceName, nil
+}
+
+func findInterfaceNameByIP(ip net.IP) (string, error) {
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return "", fmt.Errorf("failed to list interfaces: %v", err)
+	}
+
+	for _, iface := range interfaces {
+		addrs, err := iface.Addrs()
+		if err != nil {
+			return "", fmt.Errorf("failed to get addresses for interface %s: %v", iface.Name, err)
+		}
+
+		for _, addr := range addrs {
+			var ifaceIP net.IP
+			switch v := addr.(type) {
+			case *net.IPNet:
+				ifaceIP = v.IP
+			case *net.IPAddr:
+				ifaceIP = v.IP
+			}
+
+			if ifaceIP != nil && ifaceIP.Equal(ip) {
+				return iface.Name, nil
+			}
+		}
+	}
+
+	return "", fmt.Errorf("no interface found for IP %s", ip)
+}