Merge branch 'main' into dev

Signed-off-by: Derek Collison <derek@nats.io>

server/events.go

@@ -56,6 +56,8 @@ 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         = "$SYS.SERVER.%s.SHUTDOWN"
 	shutdownEventSubj         = "$SYS.SERVER.%s.SHUTDOWN"
 	clientKickReqSubj         = "$SYS.REQ.SERVER.%s.KICK"
 	clientLDMReqSubj          = "$SYS.REQ.SERVER.%s.LDM"
@@ -589,6 +591,19 @@ RESET:
 	}
 }
 
+// Will send a shutdown message for lame-duck. Unlike sendShutdownEvent, this will
+// not close off the send queue or reply handler, as we may still have a workload
+// that needs migrating off.
+// Lock should be held.
+func (s *Server) sendLDMShutdownEventLocked() {
+	if s.sys == nil || s.sys.sendq == nil {
+		return
+	}
+	subj := fmt.Sprintf(lameDuckEventSubj, s.info.ID)
+	si := &ServerInfo{}
+	s.sys.sendq.push(newPubMsg(nil, subj, _EMPTY_, si, nil, si, noCompression, false, true))
+}
+
 // Will send a shutdown message.
 func (s *Server) sendShutdownEvent() {
 	s.mu.Lock()
@@ -1021,6 +1036,13 @@ 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 {