lib/metad.py

#
#

# Copyright (C) 2014 Google Inc.
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"""Module for the Metad protocol

"""

import logging
import random
import time

from ganeti import constants
from ganeti import errors
import ganeti.rpc.client as cl
from ganeti.rpc.transport import Transport
from ganeti.rpc import errors


# If the metadata daemon is disabled, there is no stub generated for it.
# So import the module and define the client class only if enabled, otherwise
# just generate an empty placeholder class.
if constants.ENABLE_METAD:
  import ganeti.rpc.stub.metad as stub

  class Client(cl.AbstractStubClient, stub.ClientRpcStub):
    """High-level Metad client implementation.

    This uses a backing Transport-like class on top of which it
    implements data serialization/deserialization.

    """
    def __init__(self, timeouts=None, transport=Transport):
      """Constructor for the Client class.

      Arguments are the same as for L{AbstractClient}.

      """
      cl.AbstractStubClient.__init__(self, timeouts, transport)
      stub.ClientRpcStub.__init__(self)

      retries = 12
      for try_no in range(0, retries):
        try:
          self._InitTransport()
          return
        except errors.TimeoutError:
          logging.debug("Timout trying to connect to MetaD")
          if try_no == retries - 1:
            raise
          logging.debug("Will retry")
          time.sleep(try_no * 10 + 10 * random.random())

    def _InitTransport(self):
      """(Re)initialize the transport if needed.

      """
      if self.transport is None:
        self.transport = self.transport_class(self._GetAddress(),
                                              timeouts=self.timeouts,
                                              allow_non_master=True)

else:
  class Client(object):
    """An empty client representation that just throws an exception.

    """
    def __init__(self, _timeouts=None, _transport=None):
      raise errors.ProgrammerError("The metadata deamon is disabled, yet"
                                   " the client has been called")