一、入门

1. 概述

2. 特点

3. 数据结构

4. 应用场景

统一命名服务：nginx也可以实现
统一配置管理：
统一集群管理：
服务器动态上下线：
软负载均衡：

二、本地

1.安装

2. 参数解读

三、集群操作

3.1.1 集群安装

遇到问题：1防火墙未关闭，2配置错误
sudo systemctl stop firewalld
加到zok.conf中：

############cluster#################
server.2=192.168.88.130:2888:3888
server.3=192.168.88.131:2888:3888
server.4=192.168.88.132:2888:3888

3.2 选举机制

1. 第一次启动

2. 非第一次启动

3.3 ZK集群启动停止脚本

#!/bin/bash
case $1 in
"start"){for i in 192.168.88.130 192.168.88.131 192.168.88.132doecho -------- zookeeper $i 启动 ------------ssh $i "/opt/module/zookeeper-3.5.7/bin/zkServer.sh start"done
}
;;
"stop"){for i in 192.168.88.130 192.168.88.131 192.168.88.132doecho -------- zookeeper $i 停止 ------------ssh $i "/opt/module/zookeeper-3.5.7/bin/zkServer.sh stop"done
}
;;
"status"){for i in 192.168.88.130 192.168.88.131 192.168.88.132doecho -------- zookeeper $i 状态 ------------ssh $i "/opt/module/zookeeper-3.5.7/bin/zkServer.sh status"done
}
;;
esac

3.4 客户端命令行操作

3.2.1 命令行语法

3.2.2 节点类型（持久/短暂/有序号/无序号）

临时节点：退出客户端以后删除
有序节点：可重复，key后自带序号

create /sanguo/shuguo/zhangfei #创建永久无序节点
create -s /sanguo/shuguo/guanyu #创建永久有序节点
create -s -e /sanguo/wuguo/zhouyu1 #创建临时有序节点
create -e /sanguo/wuguo/zhouyu2 #创建临时无序节点

3.2.4 监听器原理

3.3 删除节点

3.5 客户端API操作

3.6 监听节点变化

3.7 判断Znode是否存在

3.8 写数据原理

分为两种情况：
1、请求发送给Leader节点；

1. Client发送write请求给Leader，Leader收到消息先写
2. Leader将write请求转发给下一个Follower节点，Follow收到写入 完成后回一个ack给上一个节点（Leader）
3. 大于半数的Leader节点完成写入（共3，完成2），Leader返回给Clinet一个ack表示完成
4. Leader继续给其他Follower发送write请求，Follower接收到请求写入，完成后返回ack
   

2、请求发送给Follower节点；

1. Client发送write请求给Follower，Follower收到消息先转发给Leader
2. Leader接收到write请求，先执行，然后转发给Follower
3. Follower接收到write请求。执行，然后回复一个ack
4. 大于半数节点已write，Leader返回一个ack给最先接触到Client的节点（Follower），Follower再返回一个ack给Client
5. Leader给剩下的Follower发送write请求，Follower写完回复ack给Leader
   

四、服务器动态上下线监听案例

package com.atguigu.case1;import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;import java.io.IOException;
import java.sql.Array;
import java.util.ArrayList;
import java.util.List;/*** 2023年11月24日* <p>* case1 服务器动态上下限* <p>* 1、获取zk连接* 2、监听节点* 3、业务代码（睡觉*/
public class DistributeClient {ZooKeeper zooKeeper;public static void main(String[] args) throws IOException, InterruptedException, KeeperException {DistributeClient zk = new DistributeClient();zk.connect();zk.watcherList();zk.business();}private void business() throws InterruptedException {Thread.sleep(Long.MAX_VALUE);}private void watcherList() throws InterruptedException, KeeperException {List<String> children = zooKeeper.getChildren("/servers", true, null);ArrayList<String> strings = new ArrayList<String>();for (String child : children) {byte[] data = zooKeeper.getData("/servers/" + child, false, null);strings.add(new String(data));}System.out.println(strings);}private void connect() throws IOException {String connectString = "192.168.88.130:2181,192.168.88.131:2181,192.168.88.132:2181";int sessionTimeout = 300000;zooKeeper = new ZooKeeper(connectString, sessionTimeout, new Watcher() {public void process(WatchedEvent watchedEvent) {try {watcherList();} catch (InterruptedException e) {throw new RuntimeException(e);} catch (KeeperException e) {throw new RuntimeException(e);}}});}
}

package com.atguigu.case1;import org.apache.zookeeper.*;import java.io.IOException;/*** case 1* 服务器动态上下线例子* <p>* 1. 创建zk连接* 2. 注册服务器到zk集群* 3. 业务代码（睡觉*/
public class DistributeServer {ZooKeeper zooKeeper;public static void main(String[] args) throws IOException, InterruptedException, KeeperException {DistributeServer zk = new DistributeServer();zk.connect();zk.register(args[0]);zk.business();}private void business() throws InterruptedException {Thread.sleep(Long.MAX_VALUE);}private void register(String hostName) throws InterruptedException, KeeperException {zooKeeper.create("/servers/"+hostName, hostName.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);System.out.println(hostName + "已注册上");}private void connect() throws IOException {String connectString = "192.168.88.130:2181,192.168.88.131:2181,192.168.88.132:2181";int sessionTimeout = 3000000;zooKeeper = new ZooKeeper(connectString, sessionTimeout, new Watcher() {public void process(WatchedEvent watchedEvent) {}});}}

五、ZooKeeper分布式锁案例

package com.atguigu.case2;import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;import java.io.IOException;
import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;/*** 分布式锁*/
public class DistributedLock {public ZooKeeper zooKeeper;public CountDownLatch connectLatch = new CountDownLatch(1);public CountDownLatch waitLatch = new CountDownLatch(1);private String waitPath;private String currentNode;DistributedLock() throws IOException, InterruptedException, KeeperException {//连接zkString connectString = "192.168.88.130:2181,192.168.88.131:2181,192.168.88.132:2181";int sessionTimeout = 3000;zooKeeper = new ZooKeeper(connectString, sessionTimeout, new Watcher() {public void process(WatchedEvent watchedEvent) {//连接完成后释放connectLatchif (watchedEvent.getState() == Event.KeeperState.SyncConnected) {connectLatch.countDown();}//当前锁节点为最小锁时，释放waitLatchif (watchedEvent.getType() == Event.EventType.NodeDeleted && watchedEvent.getPath().equals(waitPath)) {waitLatch.countDown();}}});//连接完成后继续执行connectLatch.await();}public void lock() throws InterruptedException, KeeperException {// 检测locks节点是否存在，不存在就建一个Stat exists = zooKeeper.exists("/locks", false);if (exists == null){zooKeeper.create("/locks",null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);}//创建锁节点currentNode = zooKeeper.create("/locks/res-",null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);// 判断是否是头一个，是的话给锁List<String> locks = zooKeeper.getChildren("/locks", false);Collections.sort(locks);//若数组内无值，说明就是第一位可以直接给锁if (locks.size() == 0){}else {//算出创建锁的位置，判断是否是最小的，是的话就给锁，否则对上一个锁进行监听int location = locks.indexOf(currentNode.substring("/locks/".length()));if (location == 0){//最小给锁}else if (location == -1){//错误System.out.println("错误");}else {waitPath = locks.get(location - 1);zooKeeper.getData(waitPath,true,null);//等待监听waitLatch.await();}}}public void unlock() throws InterruptedException, KeeperException {zooKeeper.delete(currentNode,-1);}
}

package com.atguigu.case2;import org.apache.zookeeper.KeeperException;import java.io.IOException;public class Client {public static void main(String[] args) throws IOException, InterruptedException, KeeperException {new Thread(new Runnable() {public void run() {try {DistributedLock distributedLock = new DistributedLock();distributedLock.lock();System.out.println("线程1启动，获取锁");Thread.sleep(5 * 1000);distributedLock.unlock();System.out.println("线程1释放锁");} catch (InterruptedException e) {throw new RuntimeException(e);} catch (KeeperException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}}).start();new Thread(new Runnable() {public void run() {try {DistributedLock distributedLock = new DistributedLock();distributedLock.lock();System.out.println("线程2启动，获取锁");Thread.sleep(5 * 1000);distributedLock.unlock();System.out.println("线程2释放锁");} catch (InterruptedException e) {throw new RuntimeException(e);} catch (KeeperException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}}).start();}
}

5.1、分布式锁-成熟框架curator

六、企业面试真题

EPOCH：leader任期