AAAAA Curator入门实战(Linux安装)
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Apache Curator入门实战
Curator是Netflix公司开源的一个Zookeeper客户端，与Zookeeper提供的原生客户端相比，Curator的抽象层次更高，简化了Zookeeper客户端的开发量。
1.Zookeeper安装部署
Zookeeper的部署很简单，如果已经有Java运行环境的话，下载tarball解压后即可行。
[root@vm Temp]$ wget http://mirror.bit.edu.cn/apache/zookeeper/zookeeper-3.4.6/zookeeper-3.4.6.tar.gz[root@vm Temp]$ tar zxvf zookeeper-3.4.6.tar.gz[root@vm Temp]$ cd zookeeper-3.4.6[root@vm zookeeper-3.4.6]$ cp conf/zoo_sample.cfg conf/zoo.cfg[root@vm zookeeper-3.4.6]$ export ZOOKEEPER_HOME=/usr/local/src/zookeeper-3.4.5[root@vm zookeeper-3.4.6]$ export PATH=$ZOOKEEPER_HOME/bin:$PATH[root@vm zookeeper-3.4.6]$ bin/zkServer.sh start[root@vm zookeeper-3.4.6]$ bin/zkCli.sh -server 127.0.0.1:2181
2.客户端常用操作
用zkCli.sh连接上Zookeeper服务后，用help能列出所有命令：
[root@BC-VM-edce4ac67d304079868c0bb265337bd4 zookeeper-3.4.6]# bin/zkCli.sh -127.0.0.1:2181Connecting to localhost:21812015-06-11 10:55:14,387 [myid:] - INFO [main:Environment@100] - Client environment:zookeeper.version=3.4.6-1569965, built on 02/20/2014 09:09 GMT ...[zk: localhost:2181(CONNECTED) 5] helpZooKeeper -server host:port cmd args connect host:port get path [watch] ls path [watch] set path data [version] rmr path delquota [-n|-b] path quit printwatches on|off create [-s] [-e] path data acl stat path [watch] close ls2 path [watch] history listquota path setAcl path acl getAcl path sync path redo cmdno addauth scheme auth delete path [version] setquota -n|-b val path
面就试验一下常用的命令：
- create：创建路径结点。
- ls：查看路径下的所有结点。
- get：获得结点上的值。
- set：修改结点上的值。
- delete：删除结点。
[zk: localhost:2181(CONNECTED) 6] create /zktest mydataCreated /zktest[zk: localhost:2181(CONNECTED) 12] ls /[zktest, zookeeper][zk: localhost:2181(CONNECTED) 7] ls /zktest[][zk: localhost:2181(CONNECTED) 13] get /zktestmydatacZxid = 0x1cctime = Thu Jun 11 10:58:06 CST 2015mZxid = 0x1cmtime = Thu Jun 11 10:58:06 CST 2015pZxid = 0x1ccversion = 0dataVersion = 0aclVersion = 0ephemeralOwner = 0x0dataLength = 6numChildren = 0[zk: localhost:2181(CONNECTED) 14] set /zktest junkcZxid = 0x1cctime = Thu Jun 11 10:58:06 CST 2015mZxid = 0x1fmtime = Thu Jun 11 10:59:08 CST 2015pZxid = 0x1ccversion = 0dataVersion = 1aclVersion = 0ephemeralOwner = 0x0dataLength = 4numChildren = 0[zk: localhost:2181(CONNECTED) 15] delete /zktest[zk: localhost:2181(CONNECTED) 16] ls /[zookeeper]
3.用Curator管理Zookeeper
Curator的Maven依赖如下，一般直接使用curator-recipes就行了，如果需要自己封装一些底层些的功能的话，例如增加连接管理重试机制等，则可以引入curator-framework包。
<dependency> <groupId>org.apache.curator</groupId> <artifactId>curator-recipes</artifactId> <version>2.7.0</version> </dependency>
3.1 Client操作
利用Curator提供的客户端API，可以完全实现上面原生客户端的功能。值得注意的是，Curator采用流式风格API。
package com.cdai.codebase.bigdata.hadoop.zookeeper.curator;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.retry.RetryNTimes;/** * Curator framework's client test. * Output: * $ create /zktest hello * $ ls / * [zktest, zookeeper] * $ get /zktest * hello * $ set /zktest world * $ get /zktest * world * $ delete /zktest * $ ls / * [zookeeper] */public class CuratorClientTest { /** Zookeeper info */ private static final String ZK_ADDRESS = "192.168.1.100:2181"; private static final String ZK_PATH = "/zktest"; public static void main(String[] args) throws Exception { // 1.Connect to zk CuratorFramework client = CuratorFrameworkFactory.newClient( ZK_ADDRESS, new RetryNTimes(10, 5000) ); client.start(); System.out.println("zk client start successfully!"); // 2.Client API test // 2.1 Create node String data1 = "hello"; print("create", ZK_PATH, data1); client.create(). creatingParentsIfNeeded(). forPath(ZK_PATH, data1.getBytes()); // 2.2 Get node and data print("ls", "/"); print(client.getChildren().forPath("/")); print("get", ZK_PATH); print(client.getData().forPath(ZK_PATH)); // 2.3 Modify data String data2 = "world"; print("set", ZK_PATH, data2); client.setData().forPath(ZK_PATH, data2.getBytes()); print("get", ZK_PATH); print(client.getData().forPath(ZK_PATH)); // 2.4 Remove node print("delete", ZK_PATH); client.delete().forPath(ZK_PATH); print("ls", "/"); print(client.getChildren().forPath("/")); } private static void print(String... cmds) { StringBuilder text = new StringBuilder("$ "); for (String cmd : cmds) { text.append(cmd).append(" "); } System.out.println(text.toString()); } private static void print(Object result) { System.out.println( result instanceof byte[] ? new String((byte[]) result) : result); }}3.2 监听器
Curator提供了三种Watcher(Cache)来监听结点的变化：
- Path Cache：监视一个路径下1）孩子结点的创建、2）删除，3）以及结点数据的更新。产生的事件会传递给注册的PathChildrenCacheListener。
- Node Cache：监视一个结点的创建、更新、删除，并将结点的数据缓存在本地。
- Tree Cache：Path Cache和Node Cache的“合体”，监视路径下的创建、更新、删除事件，并缓存路径下所有孩子结点的数据。
下面就测试一下最简单的Path Watcher：
package com.cdai.codebase.bigdata.hadoop.zookeeper.curator;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.cache.ChildData;import org.apache.curator.framework.recipes.cache.PathChildrenCache;import org.apache.curator.framework.recipes.cache.PathChildrenCache.StartMode;import org.apache.curator.retry.RetryNTimes;/** * Curator framework watch test. */public class CuratorWatcherTest { /** Zookeeper info */ private static final String ZK_ADDRESS = "192.168.1.100:2181"; private static final String ZK_PATH = "/zktest"; public static void main(String[] args) throws Exception { // 1.Connect to zk CuratorFramework client = CuratorFrameworkFactory.newClient( ZK_ADDRESS, new RetryNTimes(10, 5000) ); client.start(); System.out.println("zk client start successfully!"); // 2.Register watcher PathChildrenCache watcher = new PathChildrenCache( client, ZK_PATH, true // if cache data ); watcher.getListenable().addListener((client1, event) -> { ChildData data = event.getData(); if (data == null) { System.out.println("No data in event[" + event + "]"); } else { System.out.println("Receive event: " + "type=[" + event.getType() + "]" + ", path=[" + data.getPath() + "]" + ", data=[" + new String(data.getData()) + "]" + ", stat=[" + data.getStat() + "]"); } }); watcher.start(StartMode.BUILD_INITIAL_CACHE); System.out.println("Register zk watcher successfully!"); Thread.sleep(Integer.MAX_VALUE); }}下面是在zkCli.sh中操作时Java程序的输出：
Java: zk client start successfully!Java: Register zk watcher successfully!zkCli: [zk: localhost:2181(CONNECTED) 11] create /zktest/hello mydataJava: Receive event: type=[CHILD_ADDED], path=[/zktest/hello], data=[mydata], stat=[121,121,1434001221097,1434001221097,0,0,0,0,6,0,121]zkCli: [zk: localhost:2181(CONNECTED) 12] set /zktest/hello otherdataJava: Receive event: type=[CHILD_UPDATED], path=[/zktest/hello], data=[otherdata], stat=[121,122,1434001221097,1434001228467,1,0,0,0,9,0,121]zkCli: [zk: localhost:2181(CONNECTED) 13] delete /zktest/helloJava: Receive event: type=[CHILD_REMOVED], path=[/zktest/hello], data=[otherdata], stat=[121,122,1434001221097,1434001228467
4.Curator“菜谱”
既然Maven包叫做curator-recipes，那说明Curator有它独特的“菜谱”- 锁：包括共享锁、共享可重入锁、读写锁等。
- 选举：Leader选举算法。
- Barrier：阻止分布式计算直至某个条件被满足的“栅栏”，可以看做JDK Concurrent包中Barrier的分布式实现。
- 缓存：前面提到过的三种Cache及监听机制。
- 持久化结点：连接或Session终止后仍然在Zookeeper中存在的结点。
- 队列：分布式队列、分布式优先级队列等。
4.1 分布式锁
分布式编程时，比如最容易碰到的情况就是应用程序在线上多机部署，于是当多个应用同时访问某一资源时，就需要某种机制去协调它们。例如，现在一台应用正在rebuild缓存内容，要临时锁住某个区域暂时不让访问；又比如调度程序每次只想一个任务被一台应用执行等等。
下面的程序会启动两个线程t1和t2去争夺锁，拿到锁的线程会占用5秒。运行多次可以观察到，有时是t1先拿到锁而t2等待，有时又会反过来。Curator会用我们提供的lock路径的结点作为全局锁，这个结点的数据类似这种格式：[_c_64e0811f-9475-44ca-aa36-c1db65ae5350-lock-0000000005]，每次获得锁时会生成这种串，释放锁时清空数据。
package com.cdai.codebase.bigdata.hadoop.zookeeper.curator;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.RetryNTimes;import java.util.concurrent.TimeUnit;/** * Curator framework's distributed lock test. */public class CuratorDistrLockTest { /** Zookeeper info */ private static final String ZK_ADDRESS = "192.168.1.100:2181"; private static final String ZK_LOCK_PATH = "/zktest"; public static void main(String[] args) throws InterruptedException { // 1.Connect to zk CuratorFramework client = CuratorFrameworkFactory.newClient( ZK_ADDRESS, new RetryNTimes(10, 5000) ); client.start(); System.out.println("zk client start successfully!"); Thread t1 = new Thread(() -> { doWithLock(client); }, "t1"); Thread t2 = new Thread(() -> { doWithLock(client); }, "t2"); t1.start(); t2.start(); } private static void doWithLock(CuratorFramework client) { InterProcessMutex lock = new InterProcessMutex(client, ZK_LOCK_PATH); try { if (lock.acquire(10 * 1000, TimeUnit.SECONDS)) { System.out.println(Thread.currentThread().getName() + " hold lock"); Thread.sleep(5000L); System.out.println(Thread.currentThread().getName() + " release lock"); } } catch (Exception e) { e.printStackTrace(); } finally { try { lock.release(); } catch (Exception e) { e.printStackTrace(); } } }}4.2 Leader选举
当集群里的某个服务down机时，我们可能要从slave结点里选出一个作为新的master，这时就需要一套能在分布式环境中自动协调的Leader选举方法。Curator提供了LeaderSelector监听器实现Leader选举功能。同一时刻，只有一个Listener会进入takeLeadership()方法，说明它是当前的Leader。注意：当Listener从takeLeadership()退出时就说明它放弃了“Leader身份”，这时Curator会利用Zookeeper再从剩余的Listener中选出一个新的Leader。autoRequeue()方法使放弃Leadership的Listener有机会重新获得Leadership，如果不设置的话放弃了的Listener是不会再变成Leader
package com.cdai.codebase.bigdata.hadoop.zookeeper.curator;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.leader.LeaderSelector;import org.apache.curator.framework.recipes.leader.LeaderSelectorListener;import org.apache.curator.framework.state.ConnectionState;import org.apache.curator.retry.RetryNTimes;import org.apache.curator.utils.EnsurePath;/** * Curator framework's leader election test. * Output: * LeaderSelector-2 take leadership! * LeaderSelector-2 relinquish leadership! * LeaderSelector-1 take leadership! * LeaderSelector-1 relinquish leadership! * LeaderSelector-0 take leadership! * LeaderSelector-0 relinquish leadership! * ... */public class CuratorLeaderTest { /** Zookeeper info */ private static final String ZK_ADDRESS = "192.168.1.100:2181"; private static final String ZK_PATH = "/zktest"; public static void main(String[] args) throws InterruptedException { LeaderSelectorListener listener = new LeaderSelectorListener() { @Override public void takeLeadership(CuratorFramework client) throws Exception { System.out.println(Thread.currentThread().getName() + " take leadership!"); // takeLeadership() method should only return when leadership is being relinquished. Thread.sleep(5000L); System.out.println(Thread.currentThread().getName() + " relinquish leadership!"); } @Override public void stateChanged(CuratorFramework client, ConnectionState state) { } }; new Thread(() -> { registerListener(listener); }).start(); new Thread(() -> { registerListener(listener); }).start(); new Thread(() -> { registerListener(listener); }).start(); Thread.sleep(Integer.MAX_VALUE); } private static void registerListener(LeaderSelectorListener listener) { // 1.Connect to zk CuratorFramework client = CuratorFrameworkFactory.newClient( ZK_ADDRESS, new RetryNTimes(10, 5000) ); client.start(); // 2.Ensure path try { new EnsurePath(ZK_PATH).ensure(client.getZookeeperClient()); } catch (Exception e) { e.printStackTrace(); } // 3.Register listener LeaderSelector selector = new LeaderSelector(client, ZK_PATH, listener); selector.autoRequeue(); selector.start(); }} 0 0
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