zookeeper适用场景：如何竞选Master及代码实现

#!/usr/bin/env python2.7
# -*- coding: UTF-8 -*-

import logging
from os.path import basename, join

from zkclient import ZKClient, zookeeper, watchmethod

logging.basicConfig(
    level = logging.DEBUG,
    format = "[%(asctime)s] %(levelname)-8s %(message)s"
)

log = logging

class GJZookeeper(object):

    ZK_HOST = "localhost:2181"
    ROOT = "/Roles"
    WORKERS_PATH = join(ROOT, "workers")
    MASTERS_NUM = 1
    TIMEOUT = 10000

    def __init__(self, verbose = True):
        self.VERBOSE = verbose
        self.masters = []
        self.is_master = False
        self.path = None

        self.zk = ZKClient(self.ZK_HOST, timeout = self.TIMEOUT)
        self.say("login ok!")
        # init
        self.__init_zk()
        # register
        self.register()

    def __init_zk(self):
        """
        create the zookeeper node if not exist
        |-Roles
             |-workers
        """
        nodes = (self.ROOT, self.WORKERS_PATH)
        for node in nodes: 
            if not self.zk.exists(node):
                try:
                    self.zk.create(node, "")
                except:
                    pass

    @property
    def is_slave(self):
        return not self.is_master

    def register(self):
        """
        register a node for this worker,znode type : EPHEMERAL | SEQUENCE
        |-Roles
             |-workers
                     |-worker000000000x         ==>>master
                     |-worker000000000x+1       ==>>worker
                     ....
        """
        self.path = self.zk.create(self.WORKERS_PATH + "/worker", "1", flags=zookeeper.EPHEMERAL | zookeeper.SEQUENCE)
        self.path = basename(self.path)
        self.say("register ok! I‘m %s" % self.path)
        # check who is the master
        self.get_master()

    def get_master(self):
        """
        get children, and check who is the smallest child
        """
        @watchmethod
        def watcher(event):
            self.say("child changed, try to get master again.")
            self.get_master()
        try :
            children = self.zk.get_children(self.WORKERS_PATH, watcher)
        except zookeeper.ConnectionLossException:
            print "losing connection with zookeeper..."
            return False
        except :
            return False
        children.sort()
        self.say("%s‘s children: %s" % (self.WORKERS_PATH, children)) 

        # check if I‘m master
        self.masters = children[:self.MASTERS_NUM]
        if self.path in self.masters:
            self.is_master = True
            self.say("I‘ve become master!")
        else:
            self.say("%s is masters, I‘m slave" % self.masters)


    def say(self, msg):
        """
        print messages to screen
        """
        if self.VERBOSE:
            if self.path:
                log.info("[ %s(%s) ] %s" % (self.path, "master" if self.is_master else "slave", msg))
            else:
                log.info(msg)

def main():
    gj_zookeeper = GJZookeeper()

if __name__ == "__main__":
    main()
    import time
    time.sleep(1000)