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《ZooKeeper终极指南》

news 2025/9/23 9:51:02

一、ZooKeeper是什么？为什么分布式系统离不开它？

ZooKeeper是一个分布式的、开放源码的分布式应用程序协调服务，是Google的Chubby一个开源的实现，是Hadoop和HBase的重要组件。

核心功能：

配置管理：集中管理集群配置信息
命名服务：分布式系统节点命名
分布式同步：节点间的数据同步
集群管理：节点状态监控和Leader选举

二、ZooKeeper核心概念解析

1. 数据模型：ZNode

ZooKeeper的数据模型采用层次化的树形结构，每个节点称为ZNode。

# 典型的ZNode路径
/app1/config/database/redis/nodes/node0001/node0002

ZNode类型：

持久节点：永久存在，除非显式删除
临时节点：客户端会话结束时自动删除
顺序节点：自动在节点名后加上顺序编号

2. 版本机制

每个ZNode都有以下版本信息：

version：数据版本号
cversion：子节点版本号
aversion：ACL版本号

3. Watcher机制

客户端可以在ZNode上设置监听器，当节点发生变化时，ZooKeeper会向客户端发送通知。

三、ZooKeeper集群架构

集群角色：

角色	职责	数量要求
Leader	处理所有写请求，发起投票	1个
Follower	处理读请求，参与投票	至少2个
Observer	处理读请求，不参与投票	可选

选举算法：Zab协议

ZooKeeper使用Zab（ZooKeeper Atomic Broadcast）协议保证分布式一致性。

// 简化的选举过程
public class Election {private long myId;private long currentLeader;public void startElection() {// 1. 每个节点投票给自己// 2. 交换投票信息// 3. 选择zxid最大的节点为Leader// 4. 如果zxid相同，选择serverId最大的}
}

四、ZooKeeper安装与配置

1. 单机模式安装

# 下载解压
wget https://archive.apache.org/dist/zookeeper/zookeeper-3.6.3/apache-zookeeper-3.6.3-bin.tar.gz
tar -zxvf apache-zookeeper-3.6.3-bin.tar.gz
cd apache-zookeeper-3.6.3-bin# 配置
cp conf/zoo_sample.cfg conf/zoo.cfg
./bin/zkServer.sh start

2. 集群模式配置

# conf/zoo.cfg
tickTime=2000
dataDir=/var/lib/zookeeper
clientPort=2181
initLimit=5
syncLimit=2
server.1=zk1:2888:3888
server.2=zk2:2888:3888
server.3=zk3:2888:3888

3. 客户端连接

# 命令行客户端
./bin/zkCli.sh -server localhost:2181# 常用命令
[zk: localhost:2181] ls /
[zk: localhost:2181] create /test "data"
[zk: localhost:2181] get /test
[zk: localhost:2181] set /test "new data"

五、Java客户端实战

1. 添加依赖

<dependency><groupId>org.apache.zookeeper</groupId><artifactId>zookeeper</artifactId><version>3.6.3</version>
</dependency>

2. 基本操作示例

public class ZooKeeperClient {private ZooKeeper zk;private CountDownLatch connectedSignal = new CountDownLatch(1);// 连接ZooKeeperpublic void connect(String hosts) throws IOException, InterruptedException {zk = new ZooKeeper(hosts, 5000, new Watcher() {public void process(WatchedEvent we) {if (we.getState() == Event.KeeperState.SyncConnected) {connectedSignal.countDown();}}});connectedSignal.await();}// 创建节点public void create(String path, byte[] data) throws KeeperException, InterruptedException {zk.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);}// 读取数据public String getData(String path) throws KeeperException, InterruptedException {byte[] data = zk.getData(path, false, null);return new String(data, "UTF-8");}// 设置监听器public void watchNode(String path) throws KeeperException, InterruptedException {zk.getData(path, new Watcher() {public void process(WatchedEvent we) {if (we.getType() == Event.EventType.NodeDataChanged) {System.out.println("节点数据发生变化: " + path);}}}, null);}
}

3. 分布式锁实现

public class DistributedLock {private ZooKeeper zk;private String lockPath;private String currentPath;public boolean tryLock() throws KeeperException, InterruptedException {// 创建临时顺序节点currentPath = zk.create(lockPath + "/lock-", null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);// 获取所有锁节点并排序List<String> children = zk.getChildren(lockPath, false);Collections.sort(children);// 判断当前节点是否是最小的String smallest = children.get(0);return currentPath.endsWith(smallest);}public void unlock() throws KeeperException, InterruptedException {zk.delete(currentPath, -1);}
}

六、典型应用场景

1. 配置管理

public class ConfigManager {private Map<String, String> config = new HashMap<>();public void init() throws Exception {// 监听配置节点zk.getData("/app/config", new Watcher() {public void process(WatchedEvent event) {if (event.getType() == Event.EventType.NodeDataChanged) {loadConfig(); // 重新加载配置}}}, null);loadConfig();}private void loadConfig() throws Exception {byte[] data = zk.getData("/app/config", false, null);// 解析配置并更新内存config = parseConfig(new String(data));}
}

2. 服务发现

public class ServiceDiscovery {private List<String> servers = new ArrayList<>();public void watchServices() throws Exception {// 监听服务节点zk.getChildren("/services", new Watcher() {public void process(WatchedEvent event) {if (event.getType() == Event.EventType.NodeChildrenChanged) {updateServers(); // 更新服务列表}}});updateServers();}private void updateServers() throws Exception {List<String> children = zk.getChildren("/services", false);servers = children.stream().map(path -> getServerData("/services/" + path)).collect(Collectors.toList());}
}

3. Leader选举

public class LeaderElection {private String currentPath;private boolean isLeader = false;public void participate() throws Exception {// 创建临时顺序节点currentPath = zk.create("/election/node-", null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);// 监听前一个节点watchPreviousNode();}private void watchPreviousNode() throws Exception {List<String> nodes = zk.getChildren("/election", false);Collections.sort(nodes);int currentIndex = nodes.indexOf(currentPath);if (currentIndex == 0) {becomeLeader(); // 成为Leader} else {String previousNode = nodes.get(currentIndex - 1);// 监听前一个节点zk.exists("/election/" + previousNode, new Watcher() {public void process(WatchedEvent event) {if (event.getType() == Event.EventType.NodeDeleted) {watchPreviousNode(); // 重新检查}}});}}private void becomeLeader() {isLeader = true;System.out.println("成为Leader节点");}
}

七、最佳实践与性能优化

1. 配置优化

# zoo.cfg 优化配置
tickTime=2000
initLimit=10
syncLimit=5
maxClientCnxns=60
minSessionTimeout=4000
maxSessionTimeout=40000
autopurge.snapRetainCount=3
autopurge.purgeInterval=1

2. 监控指标

指标	说明	正常范围
zk_avg_latency	平均响应时间	< 10ms
zk_outstanding_requests	堆积请求数	< 10
zk_znode_count	ZNode数量	< 10万
zk_watch_count	Watch数量	< 5万

3. 常见问题排查

# 查看服务器状态
echo stat | nc localhost 2181# 查看连接详情
echo cons | nc localhost 2181# 查看Watch统计
echo wchs | nc localhost 2181# 查看节点详情
echo dump | nc localhost 2181

八、ZooKeeper vs 其他协调服务

特性	ZooKeeper	etcd	Consul
一致性算法	Zab	Raft	Raft
读写性能	写慢读快	读写均衡	读写均衡
Watch机制	一次性监听	长连接监听	长连接监听
健康检查	会话机制	心跳检查	多种检查方式
适用场景	Hadoop生态	Kubernetes	服务发现