FUSE mount: support multiple filers

fix https://github.com/chrislusf/seaweedfs/issues/2015
fix https://github.com/chrislusf/seaweedfs/issues/1531

weed/filesys/wfs_filer_client.go

@@ -1,6 +1,7 @@
 package filesys
 
 import (
+	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/util"
 	"google.golang.org/grpc"
 
@@ -10,20 +11,36 @@ import (
 
 var _ = filer_pb.FilerClient(&WFS{})
 
-func (wfs *WFS) WithFilerClient(fn func(filer_pb.SeaweedFilerClient) error) error {
+func (wfs *WFS) WithFilerClient(fn func(filer_pb.SeaweedFilerClient) error) (err error) {
 
-	err := util.Retry("filer grpc "+wfs.option.FilerGrpcAddress, func() error {
-		return pb.WithCachedGrpcClient(func(grpcConnection *grpc.ClientConn) error {
-			client := filer_pb.NewSeaweedFilerClient(grpcConnection)
-			return fn(client)
-		}, wfs.option.FilerGrpcAddress, wfs.option.GrpcDialOption)
+	return util.Retry("filer grpc", func() error {
+
+		i := wfs.option.filerIndex
+		n := len(wfs.option.FilerGrpcAddresses)
+		for x := 0; x < n; x++ {
+
+			filerGrpcAddress := wfs.option.FilerGrpcAddresses[i]
+			err = pb.WithCachedGrpcClient(func(grpcConnection *grpc.ClientConn) error {
+				client := filer_pb.NewSeaweedFilerClient(grpcConnection)
+				return fn(client)
+			}, filerGrpcAddress, wfs.option.GrpcDialOption)
+
+			if err != nil {
+				glog.V(0).Infof("WithFilerClient %d %v: %v", x, filerGrpcAddress, err)
+			} else {
+				wfs.option.filerIndex = i
+				return nil
+			}
+
+			i++
+			if i >= n {
+				i = 0
+			}
+
+		}
+		return err
 	})
 
-	if err == nil {
-		return nil
-	}
-	return err
-
 }
 
 func (wfs *WFS) AdjustedUrl(location *filer_pb.Location) string {