Use own subject for LDM event

Signed-off-by: Neil Twigg <neil@nats.io>

server/events.go

@@ -56,6 +56,7 @@ const (
 	connsRespSubj            = "$SYS._INBOX_.%s"
 	accConnsEventSubjNew     = "$SYS.ACCOUNT.%s.SERVER.CONNS"
 	accConnsEventSubjOld     = "$SYS.SERVER.ACCOUNT.%s.CONNS" // kept for backward compatibility
+	lameDuckEventSubj        = "$SYS.SERVER.%s.LAMEDUCK"
 	shutdownEventSubj        = "$SYS.SERVER.%s.SHUTDOWN"
 	authErrorEventSubj       = "$SYS.SERVER.%s.CLIENT.AUTH.ERR"
 	serverStatsSubj          = "$SYS.SERVER.%s.STATSZ"
@@ -541,7 +542,7 @@ func (s *Server) sendLDMShutdownEventLocked() {
 	if s.sys == nil || s.sys.sendq == nil {
 		return
 	}
-	subj := fmt.Sprintf(shutdownEventSubj, s.info.ID)
+	subj := fmt.Sprintf(lameDuckEventSubj, s.info.ID)
 	si := &ServerInfo{}
 	s.sys.sendq.push(newPubMsg(nil, subj, _EMPTY_, si, nil, si, noCompression, false, true))
 }
@@ -957,6 +958,13 @@ func (s *Server) initEventTracking() {
 	if _, err := s.sysSubscribe(subject, s.noInlineCallback(s.remoteServerShutdown)); err != nil {
 		s.Errorf("Error setting up internal tracking: %v", err)
 	}
+	// Listen for servers entering lame-duck mode.
+	// NOTE: This currently is handled in the same way as a server shutdown, but has
+	// a different subject in case we need to handle differently in future.
+	subject = fmt.Sprintf(lameDuckEventSubj, "*")
+	if _, err := s.sysSubscribe(subject, s.noInlineCallback(s.remoteServerShutdown)); err != nil {
+		s.Errorf("Error setting up internal tracking: %v", err)
+	}
 	// Listen for account claims updates.
 	subscribeToUpdate := true
 	if s.accResolver != nil {

server/events_test.go

@@ -1666,7 +1666,7 @@ func TestSystemAccountWithGateways(t *testing.T) {
 
 	// If this tests fails with wrong number after 10 seconds we may have
 	// added a new inititial subscription for the eventing system.
-	checkExpectedSubs(t, 45, sa)
+	checkExpectedSubs(t, 46, sa)
 
 	// Create a client on B and see if we receive the event
 	urlb := fmt.Sprintf("nats://%s:%d", ob.Host, ob.Port)