clientv3/snapshot/v3_snapshot.go
func (s *v3Manager) Save(ctx context.Context, cfg clientv3.Config, dbPath string) error {
	if len(cfg.Endpoints) != 1 {
		return fmt.Errorf("snapshot must be requested to one selected node, not multiple %v", cfg.Endpoints)
	}
	cli, err := clientv3.New(cfg)
	if err != nil {
		return err
	}
	defer cli.Close()

	partpath := dbPath + ".part"
	defer os.RemoveAll(partpath)

	var f *os.File
	f, err = os.OpenFile(partpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, fileutil.PrivateFileMode)
	if err != nil {
		return fmt.Errorf("could not open %s (%v)", partpath, err)
	}
	s.lg.Info(
		"created temporary db file",
		zap.String("path", partpath),
	)

	now := time.Now()
	var rd io.ReadCloser
	rd, err = cli.Snapshot(ctx)
	if err != nil {
		return err
	}
	s.lg.Info(
		"fetching snapshot",
		zap.String("endpoint", cfg.Endpoints[0]),
	)
	if _, err = io.Copy(f, rd); err != nil {
		return err
	}
	if err = fileutil.Fsync(f); err != nil {
		return err
	}
	if err = f.Close(); err != nil {
		return err
	}
	s.lg.Info(
		"fetched snapshot",
		zap.String("endpoint", cfg.Endpoints[0]),
		zap.Duration("took", time.Since(now)),
	)

	if err = os.Rename(partpath, dbPath); err != nil {
		return fmt.Errorf("could not rename %s to %s (%v)", partpath, dbPath, err)
	}
	s.lg.Info("saved", zap.String("path", dbPath))
	return nil
}
func (s *v3Manager) Save(ctx context.Context, cfg clientv3.Config, dbPath string) error {
	if len(cfg.Endpoints) != 1 {
		return fmt.Errorf("snapshot must be requested to one selected node, not multiple %v", cfg.Endpoints)
	}
	cli, err := clientv3.New(cfg)
	if err != nil {
		return err
	}
	defer cli.Close()

	partpath := dbPath + ".part"
	defer os.RemoveAll(partpath)

	var f *os.File
	f, err = os.OpenFile(partpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, fileutil.PrivateFileMode)
	if err != nil {
		return fmt.Errorf("could not open %s (%v)", partpath, err)
	}
	s.lg.Info(
		"created temporary db file",
		zap.String("path", partpath),
	)

	now := time.Now()
	var rd io.ReadCloser
	rd, err = cli.Snapshot(ctx)
	if err != nil {
		return err
	}
	s.lg.Info(
		"fetching snapshot",
		zap.String("endpoint", cfg.Endpoints[0]),
	)
	if _, err = io.Copy(f, rd); err != nil {
		return err
	}
	if err = fileutil.Fsync(f); err != nil {
		return err
	}
	if err = f.Close(); err != nil {
		return err
	}
	s.lg.Info(
		"fetched snapshot",
		zap.String("endpoint", cfg.Endpoints[0]),
		zap.Duration("took", time.Since(now)),
	)

	if err = os.Rename(partpath, dbPath); err != nil {
		return fmt.Errorf("could not rename %s to %s (%v)", partpath, dbPath, err)
	}
	s.lg.Info("saved", zap.String("path", dbPath))
	return nil
}
// Save fetches snapshot from remote etcd server and saves data to target path.