make tunnel logic idempotent

Loadbalancers only sync once, so the tunnel logic didn't require to be
called multiple times, however, with Gateway we can sync and change
listeners and ports, so we need to make the tunnel logic idempotent and
reconcile the host data plane with the configured portmaps.

Author: aojea

pkg/tunnels/tunnel.go

@@ -41,31 +41,49 @@ func (t *TunnelManager) SetupTunnels(containerName string) error {
 	}
 
 	klog.V(0).Infof("setting IPv4 address %s associated to container %s", ipv4, containerName)
-	output, err := AddIPToLocalInterface(ipv4)
-	if err != nil {
-		return fmt.Errorf("error adding IP to local interface: %w - %s", err, output)
+	// check if the IP is already assigned to the local interface
+	if !ipOnHost(ipv4) {
+		output, err := AddIPToLocalInterface(ipv4)
+		if err != nil {
+			return fmt.Errorf("error adding IP to local interface: %w - %s", err, output)
+		}
 	}
 
 	// create tunnel from the ip:svcport to the localhost:portmap
 	t.mu.Lock()
 	defer t.mu.Unlock()
+	_, ok := t.tunnels[containerName]
+	if !ok {
+		t.tunnels[containerName] = map[string]*tunnel{}
+	}
+
+	// Reconcile: Remove tunnels that are not in portmaps
+	for containerPort, tun := range t.tunnels[containerName] {
+		if _, ok := portmaps[containerPort]; !ok {
+			klog.V(0).Infof("removing tunnel for %s %s as it is no longer in portmaps", containerName, containerPort)
+			tun.Stop() // nolint: errcheck
+			delete(t.tunnels[containerName], containerPort)
+		}
+	}
+
 	// There is one IP per Service and a tunnel per Service Port
 	for containerPort, hostPort := range portmaps {
 		parts := strings.Split(containerPort, "/")
 		if len(parts) != 2 {
 			return fmt.Errorf("expected format port/protocol for container port, got %s", containerPort)
 		}
 
+		if _, ok := t.tunnels[containerName][containerPort]; ok {
+			klog.V(2).Infof("tunnel for %s %s already exists", containerName, containerPort)
+			continue
+		}
+
 		tun := NewTunnel(ipv4, parts[0], parts[1], "localhost", hostPort)
 		// TODO check if we can leak tunnels
 		err = tun.Start()
 		if err != nil {
 			return err
 		}
-		_, ok := t.tunnels[containerName]
-		if !ok {
-			t.tunnels[containerName] = map[string]*tunnel{}
-		}
 		t.tunnels[containerName][containerPort] = tun
 	}
 	return nil
@@ -88,6 +106,7 @@ func (t *TunnelManager) RemoveTunnels(containerName string) error {
 		}
 		tunnel.Stop() // nolint: errcheck
 	}
+	delete(t.tunnels, containerName)
 
 	klog.V(0).Infof("Removing IPv4 address %s associated to local interface", tunnelIP)
 	output, err := RemoveIPFromLocalInterface(tunnelIP)
@@ -275,3 +294,29 @@ func (t *tunnel) handleUDPConnection(conn *net.UDPConn) error {
 
 	return err
 }
+
+func ipOnHost(ip string) bool {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return false
+	}
+	for _, i := range ifaces {
+		addrs, err := i.Addrs()
+		if err != nil {
+			continue
+		}
+		for _, addr := range addrs {
+			var ipAddr net.IP
+			switch v := addr.(type) {
+			case *net.IPNet:
+				ipAddr = v.IP
+			case *net.IPAddr:
+				ipAddr = v.IP
+			}
+			if ipAddr != nil && ipAddr.String() == ip {
+				return true
+			}
+		}
+	}
+	return false
+}