View file File name : failover.py Content :#!/usr/bin/python # This program is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; either version 2 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU Library General Public License for more details. # # You should have received a copy of the GNU General Public License # along with this program; if not, write to the Free Software # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. # Copyright 2003 Jack Neely, NC State University # Here we define a base class for failover methods. The idea here is that each # failover method uses a class derived from the base class so yum only has to # worry about calling get_serverurl() and server_failed() and these classes will # figure out which URL to cough up based on the failover method. """Classes for handling failovers for server URLs.""" import random class baseFailOverMethod: """A base class to provide a failover to switch to a new server if the current one fails. """ def __init__(self, repo): self.repo = repo self.failures = 0 def get_serverurl(self, i=None): """Return a server URL based on this failover method, or None if there is a complete failure. This method should always be used to translate an index into a URL, as this object may change how indexes map. :param i: if given, this is the index of the server URL to return, instead of using the failures counter :return: the next server URL """ return None def server_failed(self): """Notify the failover method that the current server has failed. """ self.failures = self.failures + 1 def reset(self, i=0): """Reset the failures counter to the given index. :param i: the index to reset the failures counter to """ self.failures = i def get_index(self): """Return the current number of failures, which is also the current index into the list of URLs that this object represents. :fun:`get_serverurl` should always be used to translate an index into a URL, as this object may change how indexes map. :return: the current number of failures, which is also the current index """ return self.failures def len(self): """Return the total number of URLs available to cycle through in this object. :return: the total number of URLs available """ return len(self.repo.urls) class priority(baseFailOverMethod): """A class to provide a failover to switch to a new server if the current one fails. This classes chooses the next server based on the first success in the list of servers. """ def get_serverurl(self, i=None): """Return the next successful server URL in the list, or None if there is a complete failure. This method should always be used to translate an index into a URL, as this object may change how indexes map. :param i: if given, this is the index of the server URL to return, instead of using the failures counter :return: the next server URL """ if i == None: index = self.failures else: index = i if index >= len(self.repo.urls): return None return self.repo.urls[index] class roundRobin(baseFailOverMethod): """A class to provide a failover to switch to a new server if the current one fails. When an object of this class is created, it selects a random place in the list of URLs to begin with, then each time :func:`get_serveurl` is called, the next URL in the list is returned, cycling back to the beginning of the list after the end is reached. """ def __init__(self, repo): baseFailOverMethod.__init__(self, repo) random.seed() self.offset = random.randint(0, 37) def get_serverurl(self, i=None): """Return the next successful server URL in the list, using the round robin scheme, or None if there is a complete failure. This method should always be used to translate an index into a URL, as this object may change how indexes map. :param i: if given, this is the index of the server URL to return, instead of using the failures counter :return: the next server URL """ if i == None: index = self.failures else: index = i if index >= len(self.repo.urls): return None rr = (index + self.offset) % len(self.repo.urls) return self.repo.urls[rr] # SDG