portmap plugin should flush previous udp connections

conntrack does not have any way to track UDP connections, so
it relies on timers to delete a connection.
The problem is that UDP is connectionless, so a client will keep
sending traffic despite the server has gone, thus renewing the
conntrack entries.
Pods that use portmaps to expose UDP services need to flush the existing
conntrack entries on the port exposed when they are created,
otherwise conntrack will keep sending the traffic to the previous IP
until the connection age (the client stops sending traffic)

Signed-off-by: Antonio Ojea <aojea@redhat.com>

pkg/testutils/echo/client/client.go

@@ -10,19 +10,32 @@ import (
 func main() {
 	target := flag.String("target", "", "the server address")
 	payload := flag.String("message", "", "the message to send to the server")
+	protocol := flag.String("protocol", "tcp", "the protocol to use with the server [udp,tcp], default tcp")
 	flag.Parse()
 
 	if *target == "" || *payload == "" {
 		flag.Usage()
 		panic("invalid arguments")
 	}
-	conn, err := net.Dial("tcp", *target)
+
+	switch *protocol {
+	case "tcp":
+		connectTCP(*target, *payload)
+	case "udp":
+		connectUDP(*target, *payload)
+	default:
+		panic("invalid protocol")
+	}
+}
+
+func connectTCP(target, payload string) {
+	conn, err := net.Dial("tcp", target)
 	if err != nil {
-		panic(fmt.Sprintf("Failed to open connection to [%s] %v", *target, err))
+		panic(fmt.Sprintf("Failed to open connection to [%s] %v", target, err))
 	}
 	defer conn.Close()
 
-	_, err = conn.Write([]byte(*payload))
+	_, err = conn.Write([]byte(payload))
 	if err != nil {
 		panic("Failed to send payload")
 	}
@@ -30,8 +43,7 @@ func main() {
 	if err != nil {
 		panic("Failed to send payload")
 	}
-
-	buf := make([]byte, 4)
+	buf := make([]byte, 1024)
 	for {
 		n, err := conn.Read(buf)
 		fmt.Print(string(buf[:n]))
@@ -43,3 +55,36 @@ func main() {
 		}
 	}
 }
+
+// UDP uses a constant source port to trigger conntrack problems
+func connectUDP(target, payload string) {
+	LocalAddr, err := net.ResolveUDPAddr("udp", ":54321")
+	if err != nil {
+		panic(fmt.Sprintf("Failed to resolve UDP local address on port 54321 %v", err))
+	}
+	RemoteAddr, err := net.ResolveUDPAddr("udp", target)
+	if err != nil {
+		panic(fmt.Sprintf("Failed to resolve UDP remote address [%s] %v", target, err))
+	}
+	conn, err := net.DialUDP("udp", LocalAddr, RemoteAddr)
+	if err != nil {
+		panic(fmt.Sprintf("Failed to open connection to [%s] %v", target, err))
+	}
+	defer conn.Close()
+
+	_, err = conn.Write([]byte(payload))
+	if err != nil {
+		panic("Failed to send payload")
+	}
+	_, err = conn.Write([]byte("\n"))
+	if err != nil {
+		panic("Failed to send payload")
+	}
+
+	buf := make([]byte, 1024)
+	n, err := conn.Read(buf)
+	if err != nil {
+		panic("Failed to read from socket")
+	}
+	fmt.Print(string(buf[:n]))
+}