type Syncer interface {
	// SyncBase syncs the base state of the key-value state.
	// The key-value state are sent through the returned chan.
	SyncBase(ctx context.Context) (<-chan clientv3.GetResponse, chan error)
	// SyncUpdates syncs the updates of the key-value state.
	// The update events are sent through the returned chan.
	SyncUpdates(ctx context.Context) clientv3.WatchChan
}