http://www.zlovezl.cn/articles/40/
简介：
Zookeeper 分布式服务框架是 Apache Hadoop 的一个子项目，它主要是用来解决分布式应用中经常遇到的一些数据管理问题，如：统一命名服务、状态同步服务、集群管理、分布式应用配置项的管理等。
具体简介可以参照这篇文章。
zkpython的安装：
python中有一个zkpython的包，是基于zookeeper的c-client开发的，所以安装的时候需要先安装zookeeper的c客户端。安装步骤如下：
# 首先下载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 # 然后下载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
这样就完成了zkpython的安装。
一个简单的demo：
之后让我们来写一个简单的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, 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 = "/app"
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
"""
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
"""
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()
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 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)
这个简单的demo所做的事情，就是通过在zookeeper的/app/workers节点下建立临时的子节点( flags=zookeeper.EPHEMERAL | zookeeper.SEQUENCE )，每次create完成之后检查自己是不是在最小的MASTERS_NUM(例子中为1，即单master)里。如果是的话，作为master运行，否则的话，作为slave运行。
这样的话，当我们的master挂掉以后，与zookeeper之间的连接也会中断，过了指定的TIMEOUT以后，master之前在worker下的子节点就会被删除，于是slave节点之前设置的watcher会被触发，再次检查自己是否为master，如果是的话则完成切换。
demo运行结果：
# 第一个实例
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!
# 这时再起第二个实例
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
# 杀掉master，第二个实例发生的变化
[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!