Kazoo tutorial

kazoo It's a Python library , It aims to make Python Be able to relax 、 Easy to use zookeeper.

kazoo Installation

Use pip install kazoo：

pip install kazoo

because kazoo Use pure python Realization zookeeper The agreement , So you don't have to install Python zookeeper C All kinds of dependence .

Basic usage

Connection processing

Use kazoo, First you need to instantiate a KazooClient Object and establish a connection , The code is as follows ：

from kazoo.client import KazooClient

zk = KazooClient(hosts="127.0.0.1:2181")
zk.start()

By default ,KazooClient Will connect to the local network zookeeper service , The port number is 2181.

When zookeeper When the service is abnormal （ Service exception or service not started ）,zk.start() Will keep trying to reconnect , Until the connection times out .

Once the connection is established , Whether it's intermittent connection loss （ Network flash off and so on ） or zookeeper Session expiration, ,KazooClient Will keep trying to reconnect .

We can go through stop Command to explicitly disconnect ：

zk.stop()

Conversation state

Kazoo Your client is working with zookeeper During the service session , It usually switches between the following three states ：CONNECTED、 SUSPENDED、LOST.

When KazooClient When the instance is first created , Its state is LOST, Once the connection is established , The state is then switched to CONNECTED.

Throughout the life cycle of the session , With the network flash off 、 Server side zookeeper Abnormal or other reasons , The client and server are disconnected ,KazooClient Switch to SUSPENDED, meanwhile ,KazooClient Will keep trying to reconnect to the server , Once the connection is successful , The state goes back to CONNECTED.

kazoo State monitoring

Add status listening Events , Monitor the session status of client and server in real time , Once the connection is interrupted 、 When the connection is restored or the session expires , We can deal with it in time . Its usage is as follows ：

def connection_listener(state):
    if state == "LOST":
        # Register somewhere that the session was lost
        pass
    elif state == "SUSPENDED":
        # Handle being disconnected from Zookeeper
        pass
    else:
        # Handle being connected/reconnected to Zookeeper
        pass
zk = KazooClient(hosts="127.0.0.1:2181")
zk.add_listener(connection_listener)

When using kazoo.recipe.lock.Lock Or when creating temporary nodes , It is highly recommended that you add status monitoring , So that our code can correctly handle connection interruption or Zookeeper Case of session loss .

zookeeper Addition, deletion and modification of

Create nodes

Method ：

• ensure_path()： Create node paths recursively , Only permissions can be set , Can't add data .
• create()： Create nodes , And you can add data and listen for events at the same time , The premise is that its parent node must exist , Cannot create recursively .

usage ：

zk.ensure_path("/china/henan")
zk.create("/china", b"this is china node.")

Reading data

Method ：

• exists()： Check whether the node exists
• get()： Get node data and node status details
• get_children()： Gets all child nodes of the specified node

Update data

Method ：

• set()： Update the information of the specified node .

Delete node

Method ：

• delete()： Delete the specified node .

Monitor

kazoo You can add listening on the node , So that it can be triggered when the node or the child nodes of the node change .

kazoo Support two types of ways to add listeners , One is zookeeper Native supported , Its usage is as follows ：

def test_watch_data(event):
    print("this is a watcher for node data.")
zk.get_children("/china", watch=test_watch_children)

Another way is through python The principle and implementation of modifier , There are ways to support this function ：

• ChildrenWatch： Triggered when the child node changes
• DataWatch： Trigger when the node data changes

Its usage is as follows ：

@zk.ChildrenWatch("/china")
def watch_china_children(children):
    print("this is watch_china_children %s" % children)
    
@zk.DataWatch("/china")
def watch_china_node(data, state):
    print("china node is %s" % data)

kazoo Business

since v3.4 in the future ,zookeeper Support sending multiple commands at a time , These commands are submitted as an atom , Or it all works , All or nothing .

How to use it is as follows ：

transaction = zk.transaction()
transaction.check('/china/hebei', version=3)
transaction.create('/china/shanxi', b"thi is shanxi.")
results = transaction.commit()