http://www.zlovezl.cn/articles/40/

簡介：

　　Zookeeper 分布式服務框架是 Apache Hadoop 的一個子項目，它主要是用來解決分布式應用中經常遇到的一些數據管理問題，如：統一命名服務、狀態同步服務、集群管理、分布式應用配置項的管理等。

具體簡介可以參照這篇文章。

zkpython的安裝：

python中有一個zkpython的包，是基于zookeeper的c-client開發的，所以安裝的時候需要先安裝zookeeper的c客戶端。安裝步驟如下：

# 首先下載zookeeper wget http://labs.renren.com/apache-mirror//zookeeper/zookeeper-3.3.3/zookeeper-3.3.3.tar.gz tar xzvf zookeeper-3.3.3.tar.gz cd zookeeper-3.3.3/src/c/ ./configure make make install# 然后下載zkpython wget http://pypi.python.org/packages/source/z/zkpython/zkpython-0.4.tar.gz#md5=3de220615aaddf57f1462b78d32477f9 tar xzvf zkpython-0.4.tar.gz cd zkpython-0.4 python setup.py install

這樣就完成了zkpython的安裝。

一個簡單的demo：

之后讓我們來寫一個簡單的demo吧。（demo中用到的zkclient.py:https://github.com/piglei/zkpython_example/blob/master/zkclient.py）

# coding: utf-8 import logging from os.path import basename, joinfrom zkclient import ZKClient, zookeeper, watchmethodlogging.basicConfig(level = logging.DEBUG,format = "[%(asctime)s] %(levelname)-8s %(message)s" )log = loggingclass GJZookeeper(object):ZK_HOST = "localhost:2181"ROOT = "/app"WORKERS_PATH = join(ROOT, "workers")MASTERS_NUM = 1TIMEOUT = 10000def __init__(self, verbose = True):self.VERBOSE = verboseself.masters = []self.is_master = Falseself.path = Noneself.zk = ZKClient(self.ZK_HOST, timeout = self.TIMEOUT)self.say("login ok!")# initself.__init_zk()# registerself.register()def __init_zk(self):"""create the zookeeper node if not exist"""nodes = (self.ROOT, self.WORKERS_PATH)for node in nodes: if not self.zk.exists(node):try:self.zk.create(node, "")except:pass@propertydef is_slave(self):return not self.is_masterdef register(self):"""register a node for this 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 masterself.get_master()def get_master(self):"""get children, and check who is the smallest child"""@watchmethoddef watcher(event):self.say("child changed, try to get master again.")self.get_master()children = self.zk.get_children(self.WORKERS_PATH, watcher)children.sort()self.say("%s's children: %s" % (self.WORKERS_PATH, children)) # check if I'm masterself.masters = children[:self.MASTERS_NUM]if self.path in self.masters:self.is_master = Trueself.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 timetime.sleep(1000)

　　這個簡單的demo所做的事情，就是通過在zookeeper的/app/workers節點下建立臨時的子節點( flags=zookeeper.EPHEMERAL | zookeeper.SEQUENCE )，每次create完成之后檢查自己是不是在最小的MASTERS_NUM(例子中為1，即單master)里。如果是的話，作為master運行，否則的話，作為slave運行。

　　這樣的話，當我們的master掛掉以后，與zookeeper之間的連接也會中斷，過了指定的TIMEOUT以后，master之前在worker下的子節點就會被刪除，于是slave節點之前設置的watcher會被觸發，再次檢查自己是否為master，如果是的話則完成切換。

demo運行結果：

# 第一個實例 Connected in 20 ms, handle is 0 [2011-09-09 12:40:43,702] INFO???? login ok! Node /app/workers/worker created in 4 ms [2011-09-09 12:40:43,708] INFO???? [ worker0000000022(slave) ] register ok! I'm worker0000000022 [2011-09-09 12:40:43,709] INFO???? [ worker0000000022(slave) ] /app/workers's children: ['worker0000000022'] [2011-09-09 12:40:43,709] INFO???? [ worker0000000022(master) ] I've become master!# 這時再起第二個實例 Connected in 64 ms, handle is 0 [2011-09-09 12:43:08,334] INFO???? login ok! Node /app/workers/worker created in 11 ms [2011-09-09 12:43:08,346] INFO???? [ worker0000000023(slave) ] register ok! I'm worker0000000023 [2011-09-09 12:43:08,347] INFO???? [ worker0000000023(slave) ] /app/workers's children: ['worker0000000022', 'worker0000000023'] [2011-09-09 12:43:08,347] INFO???? [ worker0000000023(slave) ] ['worker0000000022'] is masters, I'm slave# 殺掉master，第二個實例發生的變化 [2011-09-09 12:44:06,016] INFO???? [ worker0000000023(slave) ] child changed, try to get master again. [2011-09-09 12:44:06,017] INFO???? [ worker0000000023(slave) ] /app/workers's children: ['worker0000000023'] [2011-09-09 12:44:06,017] INFO???? [ worker0000000023(master) ] I've become master!

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轉載于:https://www.cnblogs.com/DjangoBlog/p/3808543.html

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