Synnefo » snf-ganeti

def CheckAgreement():

  """Check the agreement on who is the master.

  The function uses a very simple algorithm: we must get more positive

  than negative answers. Since in most of the cases we are the master,

  we'll use our own config file for getting the node list. In the

  future we could collect the current node list from our (possibly

  obsolete) known nodes.

  """

  myself = utils.HostInfo().name

  #temp instantiation of a config writer, used only to get the node list

  cfg = config.ConfigWriter()

  node_list = cfg.GetNodeList()

  del cfg

  try:

    node_list.remove(myself)

  except KeyError:

    pass

  if not node_list:

    # either single node cluster, or a misconfiguration, but I won't

    # break any other node, so I can proceed

    return True

  results = rpc.call_master_info(node_list)

  if not isinstance(results, dict):

    # this should not happen (unless internal error in rpc)

    logging.critical("Can't complete rpc call, aborting master startup")

    return False

  positive = negative = 0

  other_masters = {}

  for node in results:

    if not isinstance(results[node], (tuple, list)) or len(results[node]) < 3:

      logging.warning("Can't contact node %s", node)

      continue

    master_node = results[node][2]

    if master_node == myself:

      positive += 1

    else:

      negative += 1

      if not master_node in other_masters:

        other_masters[master_node] = 0

      other_masters[master_node] += 1

  if positive <= negative:

    # bad!

    logging.critical("It seems we are not the master (%d votes for,"

                     " %d votes against)", positive, negative)

    if len(other_masters) > 1:

      logging.critical("The other nodes do not agree on a single master")

    elif other_masters:

      # TODO: resync my files from the master

      logging.critical("It seems the real master is %s",

                       other_masters.keys()[0])

    else:

      logging.critical("Can't contact any node for data, aborting startup")

    return False

  return True

  # we believe we are the master, let's ask the other nodes...

  if not CheckAgreement():

    return