add manage-loopback option

Summary:
Similar to:

https://www.internalfb.com/code/fbsource/[f9568a8498fc11ad7909787d68dbbfe3b2318b98]/fbcode/dns/gounboundwrapper/cmds/unboundwrapper/main.go?lines=31

Reviewed By: t3lurid3

Differential Revision: D52297428

fbshipit-source-id: de8ed0216ab3521dbb7b3fd3c7f2ae7a626b2ce9

cmd/ntpresponder/main.go

@@ -56,6 +56,7 @@ func main() {
 	flag.BoolVar(&debugger, "pprof", false, "Enable pprof")
 	flag.BoolVar(&s.ListenConfig.ShouldAnnounce, "announce", false, "Advertize IPs")
 	flag.DurationVar(&s.ExtraOffset, "extraoffset", 0, "Extra offset to return to clients")
+	flag.BoolVar(&s.ManageLoopback, "manage-loopback", true, "Add/remove IPs. If false, these must be managed elsewhere")
 
 	flag.Parse()
 	s.ListenConfig.IPs.SetDefault()

ntp/responder/server/ip.go

@@ -31,6 +31,9 @@ const ipv6Mask = 64
 
 // AddIPOnInterface adds ip to interface
 func (s *Server) addIPToInterface(vip net.IP) error {
+	if !s.ManageLoopback {
+		return nil
+	}
 	log.Infof("Adding %s to %s", vip, s.ListenConfig.Iface)
 	// Add IPs to the interface
 	iface, err := net.InterfaceByName(s.ListenConfig.Iface)
@@ -43,6 +46,9 @@ func (s *Server) addIPToInterface(vip net.IP) error {
 
 // deleteIPFromInterface deletes ip from interface
 func (s *Server) deleteIPFromInterface(vip net.IP) error {
+	if !s.ManageLoopback {
+		return nil
+	}
 	log.Infof("Deleting %s to %s", vip, s.ListenConfig.Iface)
 	// Delete IPs to the interface
 	iface, err := net.InterfaceByName(s.ListenConfig.Iface)

ntp/responder/server/ip_test.go

@@ -27,14 +27,20 @@ const testIP = "1.2.3.4"
 
 func TestAddIPToInterfaceError(t *testing.T) {
 	lc := ListenConfig{Iface: "lol-does-not-exist"}
-	s := &Server{ListenConfig: lc}
+	s := &Server{
+		ListenConfig:   lc,
+		ManageLoopback: true,
+	}
 	err := s.addIPToInterface(net.ParseIP(testIP))
 	require.NotNil(t, err)
 }
 
 func TestDeleteIPFromInterfaceError(t *testing.T) {
 	lc := ListenConfig{Iface: "lol-does-not-exist"}
-	s := &Server{ListenConfig: lc}
+	s := &Server{
+		ListenConfig:   lc,
+		ManageLoopback: true,
+	}
 	err := s.deleteIPFromInterface(net.ParseIP(testIP))
 	require.NotNil(t, err)
 }

ntp/responder/server/server.go

@@ -44,15 +44,16 @@ type task struct {
 
 // Server is a type for UDP server which handles connections.
 type Server struct {
-	ListenConfig ListenConfig
-	Workers      int
-	Announce     Announce
-	Stats        Stats
-	Checker      Checker
-	tasks        chan task
-	ExtraOffset  time.Duration
-	RefID        string
-	Stratum      int
+	ListenConfig   ListenConfig
+	Workers        int
+	Announce       Announce
+	Stats          Stats
+	Checker        Checker
+	tasks          chan task
+	ExtraOffset    time.Duration
+	RefID          string
+	Stratum        int
+	ManageLoopback bool
 }
 
 // Start UDP server.