I. deploy zookeeper

1. Resource planning

2. Cluster deployment

(1) install zk

[root@bigdata121 modules]# cd /opt/modules/zookeeper-3.4.10
[root@bigdata121 zookeeper-3.4.10]# mkdir zkData
[root@bigdata121 zookeeper-3.4.10]# mv conf/zoo_sample.cfg conf/zoo.cfg

(2) modify zoo.cfg configuration

# The number of milliseconds of each tick
tickTime=2000
# The number of ticks that the initial 
# synchronization phase can take
initLimit=10
# The number of ticks that can pass between 
# sending a request and getting an acknowledgement
syncLimit=5
# the directory where the snapshot is stored.
# do not use /tmp for storage, /tmp here is just 
# example sakes.
#dataDir=/tmp/zookeeper

# Specify the directory where zk stores data
dataDir=/opt/modules/zookeeper-3.4.10/zkData
# the port at which the clients will connect
clientPort=2181
# the maximum number of client connections.
# increase this if you need to handle more clients
#maxClientCnxns=60
#
# Be sure to read the maintenance section of the 
# administrator guide before turning on autopurge.
#
# http://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_maintenance
#
# The number of snapshots to retain in dataDir
#autopurge.snapRetainCount=3
# Purge task interval in hours
# Set to "0" to disable auto purge feature
#autopurge.purgeInterval=1

# Here is the key configuration
#############cluster#############################
server.1=bigdata121:2888:3888
server.2=bigdata122:2888:3888
server.3=bigdata123:2888:3888

Interpretation of cluster configuration parameters:
Server.A=B:C:D.
A is a number indicating the server number, that is, sid;
B is the ip address of the server;
C is the port where this server exchanges information with the Leader server in the cluster; it is not the external service port (the default is 2181)
D is in case the Leader server in the cluster hangs up, a port is needed to re elect and select a new Leader, and this port is used to communicate with each other when the election is executed.

Copy the entire configured program directory to other machines, use scp or rsync, and do it by yourself

(3) specify the server id
Create a "myid" file in the directory specified by the dataDir configured previously, and the contents will be written to the id of the current server, which is the only id in the zk cluster. And this id needs to be the same as that specified in the cluster in the previous configuration file, otherwise an error will be reported.

(4) configure environment variables

vim /etc/profile.d/zookeeper.sh

#!/bin/bash
export ZOOKEEPER_HOME=/opt/modules/zookeeper-3.4.10
export PATH=${ZOOKEEPER_HOME}/bin:$PATH

//Then? 
source /etc/profile.d/zookeeper.sh

(5) start
On three machines

Start up: zkServer.sh start
//View the status of zk on the current host: zkServer.sh status
[root@bigdata121 conf]# zkServer.sh status
ZooKeeper JMX enabled by default
Using config: /opt/modules/zookeeper-3.4.10/bin/../conf/zoo.cfg
Mode: follower

II. Common commands

Use zkCli.sh to enter the local zk service.
You can use the following command:

III. use of zk api (java)

1. maven dependence

<dependencies>
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.10</version>
        </dependency>
</dependencies>

2. Create zk client

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.util.List;

public class ZkTest {
    public static String connectString = "bigdata121:2181,bigdata122:2181,bigdata123:2181";
    public static int sessionTimeout = 2000;
    public ZooKeeper zkClient = null;

    @Before
    public void init() throws IOException {
        //Create zk client
        zkClient = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            //Returns the processing function of the listening event. The listening event is one-time
            public void process(WatchedEvent watchedEvent) {
                System.out.println(watchedEvent.getState() + "," + watchedEvent.getType() + "," + watchedEvent.getPath());

                try {
                    zkClient.getChildren("/", true);
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

3. Create node

public void create() {
        //Create node with parameter: node name node value permission node type
        //Open permission persistence node
        try {
            String s = zkClient.create("/wangjin", "tao".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        } catch (KeeperException e) {
            System.out.println("node exists!!!");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

4. Get child nodes

zkclient.getChildren(Path, listen or not)
//Returns a list of child nodes

//Example:
public void getChildNode() {
        try {
            List<String> children = zkClient.getChildren("/", false);
            for (String node : children) {
                System.out.println(node);
            }
        } catch (KeeperException e) {
            System.out.println("node not exists!!!");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

5. Judge whether the node exists

 zkclient.exists(path, Whether to monitor)
 //The status information of the node is returned. If it is null, the node does not exist

 //Example:
 public void nodeExist() {
        //The status information of the node is returned. If it is null, the node does not exist
        try {
            Stat stat = zkClient.exists("/king", false);
            System.out.println(stat == null ? "No," : "Yes");
        } catch (KeeperException e) {
            System.out.println("node not exists");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

IV. using zk as a distributed lock instance

1. maven dependence

<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-framework</artifactId>
    <version>4.0.0</version>
</dependency>
<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-recipes</artifactId>
    <version>4.0.0</version>
</dependency>
<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-client</artifactId>
    <version>4.0.0</version>
</dependency>
<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>16.0.1</version>
</dependency>

2, demand
In order to simulate the scene of flash buying, it is necessary to lock the quantity of goods.

3, code

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.locks.InterProcessMutex;
import org.apache.curator.retry.ExponentialBackoffRetry;

public class TestDistributedLock {

    //Define shared resources
    private static int count = 10;

    //Used to subtract goods
    private static void printCountNumber() {
        System.out.println("***********" + Thread.currentThread().getName() + "**********");
        System.out.println("Current value:" + count);
        count--;

        //Sleep for 2 seconds.
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("***********" + Thread.currentThread().getName() + "**********");
    }

    public static void main(String[] args) {
        //Define policy for client retries
        RetryPolicy policy = new ExponentialBackoffRetry(1000,  //Time to wait each time
                10); //Maximum retries

        //Define a client of ZK
        CuratorFramework client = CuratorFrameworkFactory.builder()
                .connectString("bigdata121:2181")
                .retryPolicy(policy)
                .build();

        //Client object connection zk
        client.start();
        //To create a mutex is to create a node on zk
        final InterProcessMutex lock = new InterProcessMutex(client, "/mylock");

        // Start 10 threads to access shared resources
        for (int i = 0; i < 10; i++) {
            new Thread(new Runnable() {

                public void run() {
                    try {
                        //Request to get lock
                        lock.acquire();
                        //access to shared resources
                        printCountNumber();
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    } finally {
                        //Release lock
                        try {
                            lock.release();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                }
            }).start();
        }
    }
}