Add ability to override flannel interface

pkg/agent/config/config.go

@@ -206,11 +206,20 @@ func get(envInfo *cmds.Agent) (*config.Node, error) {
 		return nil, errors.Wrapf(err, "failed to find host-local")
 	}
 
+	var flannelIface *sysnet.Interface
+	if !envInfo.NoFlannel && len(envInfo.FlannelIface) > 0 {
+		flannelIface, err = sysnet.InterfaceByName(envInfo.FlannelIface)
+		if err != nil {
+			return nil, errors.Wrapf(err, "unable to find interface")
+		}
+	}
+
 	nodeConfig := &config.Node{
 		Docker:                   envInfo.Docker,
 		NoFlannel:                envInfo.NoFlannel,
 		ContainerRuntimeEndpoint: envInfo.ContainerRuntimeEndpoint,
 	}
+	nodeConfig.FlannelIface = flannelIface
 	nodeConfig.LocalAddress = localAddress(controlConfig)
 	nodeConfig.Images = filepath.Join(envInfo.DataDir, "images")
 	nodeConfig.AgentConfig.NodeIP = nodeIP

pkg/agent/flannel/flannel.go

@@ -36,8 +36,8 @@ const (
 	subnetFile = "/run/flannel/subnet.env"
 )
 
-func flannel(ctx context.Context, flannelConf, kubeConfigFile string) error {
-	extIface, err := LookupExtIface()
+func flannel(ctx context.Context, flannelIface *net.Interface, flannelConf, kubeConfigFile string) error {
+	extIface, err := LookupExtIface(flannelIface)
 	if err != nil {
 		return err
 	}
@@ -81,14 +81,17 @@ func flannel(ctx context.Context, flannelConf, kubeConfigFile string) error {
 	return nil
 }
 
-func LookupExtIface() (*backend.ExternalInterface, error) {
-	var iface *net.Interface
+func LookupExtIface(iface *net.Interface) (*backend.ExternalInterface, error) {
 	var ifaceAddr net.IP
 	var err error
 
-	log.Info("Determining IP address of default interface")
-	if iface, err = ip.GetDefaultGatewayIface(); err != nil {
-		return nil, fmt.Errorf("failed to get default interface: %s", err)
+	if iface == nil {
+		log.Info("Determining IP address of default interface")
+		if iface, err = ip.GetDefaultGatewayIface(); err != nil {
+			return nil, fmt.Errorf("failed to get default interface: %s", err)
+		}
+	} else {
+		log.Info("Determining IP address of specified interface: ", iface.Name)
 	}
 
 	ifaceAddr, err = ip.GetIfaceIP4Addr(iface)

pkg/agent/flannel/setup.go

@@ -79,7 +79,7 @@ func Run(ctx context.Context, config *config.Node) error {
 	}
 
 	go func() {
-		err := flannel(ctx, config.FlannelConf, config.AgentConfig.KubeConfig)
+		err := flannel(ctx, config.FlannelIface, config.FlannelConf, config.AgentConfig.KubeConfig)
 		logrus.Fatalf("flannel exited: %v", err)
 	}()
 

pkg/cli/cmds/agent.go

@@ -19,6 +19,7 @@ type Agent struct {
 	Docker                   bool
 	ContainerRuntimeEndpoint string
 	NoFlannel                bool
+	FlannelIface             string
 	Debug                    bool
 	Rootless                 bool
 	AgentShared
@@ -54,6 +55,11 @@ var (
 		Usage:       "(agent) Disable embedded flannel",
 		Destination: &AgentConfig.NoFlannel,
 	}
+	FlannelIfaceFlag = cli.StringFlag{
+		Name:        "flannel-iface",
+		Usage:       "(agent) Override default flannel interface",
+		Destination: &AgentConfig.FlannelIface,
+	}
 	CRIEndpointFlag = cli.StringFlag{
 		Name:        "container-runtime-endpoint",
 		Usage:       "(agent) Disable embedded containerd and use alternative CRI implementation",
@@ -121,6 +127,7 @@ func NewAgentCommand(action func(ctx *cli.Context) error) cli.Command {
 			},
 			DockerFlag,
 			FlannelFlag,
+			FlannelIfaceFlag,
 			NodeNameFlag,
 			NodeIPFlag,
 			CRIEndpointFlag,

pkg/cli/cmds/server.go

@@ -134,6 +134,7 @@ func NewServerCommand(action func(*cli.Context) error) cli.Command {
 			NodeNameFlag,
 			DockerFlag,
 			FlannelFlag,
+			FlannelIfaceFlag,
 			CRIEndpointFlag,
 			ResolvConfFlag,
 			ExtraKubeletArgs,

pkg/daemons/config/types.go

@@ -15,6 +15,7 @@ type Node struct {
 	ContainerRuntimeEndpoint string
 	NoFlannel                bool
 	FlannelConf              string
+	FlannelIface             *net.Interface
 	LocalAddress             string
 	Containerd               Containerd
 	Images                   string