master: redirect clients to the new leader

weed/server/master_grpc_server.go

@@ -176,7 +176,7 @@ func (ms *MasterServer) KeepConnected(stream master_pb.Seaweed_KeepConnectedServ
 	}
 
 	if !ms.Topo.IsLeader() {
-		return raft.NotLeaderError
+		return ms.informNewLeader(stream)
 	}
 
 	// remember client address
@@ -236,7 +236,7 @@ func (ms *MasterServer) KeepConnected(stream master_pb.Seaweed_KeepConnectedServ
 			}
 		case <-ticker.C:
 			if !ms.Topo.IsLeader() {
-				return raft.NotLeaderError
+				return ms.informNewLeader(stream)
 			}
 		case <-stopChan:
 			return nil
@@ -245,3 +245,17 @@ func (ms *MasterServer) KeepConnected(stream master_pb.Seaweed_KeepConnectedServ
 
 	return nil
 }
+
+func (ms *MasterServer) informNewLeader(stream master_pb.Seaweed_KeepConnectedServer) error {
+	leader, err := ms.Topo.Leader()
+	if err != nil {
+		glog.Error("topo leader: %v", err)
+		return raft.NotLeaderError
+	}
+	if err := stream.Send(&master_pb.VolumeLocation{
+		Leader: leader,
+	}); err != nil {
+		return err
+	}
+	return nil
+}