[Windows] Restore lost host routes during agent initialization (antre…

…a-io#959)

When initialize the agent network on Windows node, the IP
configuration of uplink interface will be moved to OVS bridge
local interface. Which will cause the routes configured on
the uplink interface are lost.

This patch saves the routes configured on the uplink interface
before the IP configuration change and adds the saved routes on
OVS bridge local interface after that.

Signed-off-by: Rui Cao <rcao@vmware.com>

pkg/agent/agent_windows.go

@@ -21,6 +21,7 @@ import (
 	"strings"
 
 	"github.com/Microsoft/hcsshim"
+	"github.com/rakelkar/gonetsh/netroute"
 	"k8s.io/klog"
 
 	"github.com/vmware-tanzu/antrea/pkg/agent/config"
@@ -73,6 +74,12 @@ func (i *Initializer) prepareHostNetwork() error {
 		return err
 	}
 	i.nodeConfig.UplinkNetConfig.DNSServers = dnsServers
+	// Save routes which are configured on the uplink interface.
+	// The routes on the host will be lost when moving the network configuration of the uplink interface
+	// to the OVS bridge local interface. The saved routes will be restored on host after that.
+	if err = i.saveHostRoutes(); err != nil {
+		return err
+	}
 	// Create HNS network.
 	return util.PrepareHNSNetwork(i.nodeConfig.PodCIDR, i.nodeConfig.NodeIPAddr, adapter)
 }
@@ -160,6 +167,11 @@ func (i *Initializer) prepareOVSBridge() error {
 	if err = util.ConfigureInterfaceAddressWithDefaultGateway(brName, uplinkNetConfig.IP, uplinkNetConfig.Gateway); err != nil {
 		return err
 	}
+	// Restore the host routes which are lost when moving the network configuration of the uplink interface to OVS bridge interface.
+	if err = i.restoreHostRoutes(); err != nil {
+		return err
+	}
+
 	if uplinkNetConfig.DNSServers != "" {
 		if err = util.SetAdapterDNSServers(brName, uplinkNetConfig.DNSServers); err != nil {
 			return err
@@ -187,3 +199,56 @@ func (i *Initializer) initHostNetworkFlows() error {
 func (i *Initializer) getTunnelPortLocalIP() net.IP {
 	return i.nodeConfig.NodeIPAddr.IP
 }
+
+// saveHostRoutes saves routes which are configured on uplink interface before
+// the interface the configured as the uplink of antrea HNS network.
+// The routes will be restored on OVS bridge interface after the IP configuration
+// is moved to the OVS bridge.
+func (i *Initializer) saveHostRoutes() error {
+	nr := netroute.New()
+	defer nr.Exit()
+	routes, err := nr.GetNetRoutesAll()
+	if err != nil {
+		return err
+	}
+	for _, route := range routes {
+		if route.LinkIndex != i.nodeConfig.UplinkNetConfig.Index {
+			continue
+		}
+		if route.GatewayAddress.String() != i.nodeConfig.UplinkNetConfig.Gateway {
+			continue
+		}
+		// Skip IPv6 routes before we support IPv6 stack.
+		if route.DestinationSubnet.IP.To4() == nil {
+			continue
+		}
+		// Skip default route. The default route will be added automatically when
+		// configuring IP address on OVS bridge interface.
+		if route.DestinationSubnet.IP.IsUnspecified() {
+			continue
+		}
+		klog.V(4).Infof("Got host route: %v", route)
+		i.nodeConfig.UplinkNetConfig.Routes = append(i.nodeConfig.UplinkNetConfig.Routes, route)
+	}
+	return nil
+}
+
+// restoreHostRoutes restores the host routes which are lost when moving the IP
+// configuration of uplink interface to the OVS bridge interface during
+// the antrea network initialize stage.
+// The backup routes are restored after the IP configuration change.
+func (i *Initializer) restoreHostRoutes() error {
+	nr := netroute.New()
+	defer nr.Exit()
+	brInterface, err := net.InterfaceByName(i.ovsBridge)
+	if err != nil {
+		return nil
+	}
+	for _, route := range i.nodeConfig.UplinkNetConfig.Routes {
+		rt := route.(netroute.Route)
+		if err := nr.NewNetRoute(brInterface.Index, rt.DestinationSubnet, rt.GatewayAddress); err != nil {
+			return err
+		}
+	}
+	return nil
+}

pkg/agent/config/node_config.go

@@ -62,6 +62,7 @@ type AdapterNetConfig struct {
 	IP         *net.IPNet
 	Gateway    string
 	DNSServers string
+	Routes     []interface{}
 }
 
 // Local Node configurations retrieved from K8s API or host networking state.