有时爬虫会报如下超时错误：

Traceback (most recent call last):
  File "/opt/pyspider/pyspider/run.py", line 351, in <lambda>
    app.config['fetch'] = lambda x: umsgpack.unpackb(fetcher_rpc.fetch(x).data)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1233, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1587, in __request
    verbose=self.__verbose
  File "/usr/lib/python2.7/xmlrpclib.py", line 1273, in request
    return self.single_request(host, handler, request_body, verbose)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1321, in single_request
    response.msg,
ProtocolError: <ProtocolError for fetcher/: 504 Gateway Time-out>

请问有什么好的方法避免？