Zookeeper实战之选举

最近整理资料的时候发现了两年前自己写的一些Zookeeper的例子，今天整理了一下，放到这里，也许以后用的着。

首先准备一个Zookeeper集群环境，这里使用单机模拟集群环境，并使用代码方式启动服务。

Zookeeper服务

这里假定启动三个Zookeeper服务做集群

package my.zookeeperstudy;import org.apache.commons.io.FileUtils;import org.apache.zookeeper.server.quorum.QuorumPeerConfig;import org.apache.zookeeper.server.quorum.QuorumPeerMain;import java.io.File;import java.net.InetAddress;import java.util.Properties;public class ZKServer {    protected String id = null;    protected String dataDir = null;    protected String clientPort = null;    public ZKServer(String id, String dataDir, String clientPort) {        this.id = id;        this.dataDir = dataDir;        this.clientPort = clientPort;    }    public void startServer() {        new Thread(new Runnable() {            @Override            public void run() {                try {                    Properties props = new Properties();                    props.setProperty("tickTime", "2000");                    props.setProperty("dataDir", dataDir);                    FileUtils.write(new File(props.getProperty("dataDir"), "myid"), id);                    props.setProperty("clientPort", clientPort);                    props.setProperty("initLimit", "10");                    props.setProperty("syncLimit", "5");                    String hostname = InetAddress.getLocalHost().getHostName();                    props.setProperty("server.1", hostname + ":2881:3881");                    props.setProperty("server.2", hostname + ":2882:3882");                    props.setProperty("server.3", hostname + ":2883:3883");                    QuorumPeerConfig quorumConfig = new QuorumPeerConfig();                    quorumConfig.parseProperties(props);                    QuorumPeerMain quorumPeerMain = new QuorumPeerMain();                    quorumPeerMain.runFromConfig(quorumConfig);                } catch (Exception e) {                    e.printStackTrace();                }            }        }).start();    }}

package my.zookeeperstudy;public class ZKServer1 {    public static void main(String[] args) throws Exception {        ZKServer zkServer = new ZKServer("1", "/tmp/zookeeper1/data", "2181");        zkServer.startServer();    }}

package my.zookeeperstudy;public class ZKServer2 {    public static void main(String[] args) throws Exception {        ZKServer zkServer = new ZKServer("2", "/tmp/zookeeper2/data", "2182");        zkServer.startServer();    }}

package my.zookeeperstudy;public class ZKServer3 {    public static void main(String[] args) throws Exception {        ZKServer zkServer = new ZKServer("3", "/tmp/zookeeper3/data", "2183");        zkServer.startServer();    }}

测试客户端类

这里有三个客户端来模拟选举。

package my.zookeeperstudy.election;import org.apache.zookeeper.*;public class ZKClient {    protected String id = null;    protected String clientPort = null;    protected String path = "/myapp_leader";    public ZKClient(String id, String clientPort) {        this.id = id;        this.clientPort = clientPort;    }    protected void startClient() throws Exception {        ZooKeeper zk = new ZooKeeper("localhost:" + clientPort, 10000,                new Watcher() {                    public void process(WatchedEvent event) {                        System.out.println("event: " + event.getType());                    }                });        while (true) {            byte[] leader = null;            try {                leader = zk.getData(path, true, null);            } catch(Exception e) {                System.out.println("The leader is null.");            }            if (leader == null) {                try {                    zk.create(path, this.id.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);                } catch(Exception e) {                    // ignore me                }            } else {                System.out.println("The leader is: " + new String(leader));            }            Thread.sleep(1 * 1000);        }    }}

package my.zookeeperstudy.election;public class ZKClient1 {    public static void main(String[] args) throws Exception {        ZKClient zkClient = new ZKClient("1", "2181");        zkClient.startClient();    }}

package my.zookeeperstudy.election;public class ZKClient2 {    public static void main(String[] args) throws Exception {        ZKClient zkClient = new ZKClient("2", "2182");        zkClient.startClient();    }}

package my.zookeeperstudy.election;public class ZKClient3 {    public static void main(String[] args) throws Exception {        ZKClient zkClient = new ZKClient("3", "2183");        zkClient.startClient();    }}

测试

• 首先依次启动ZKServer1，ZKServer2和ZKServer3，启动过程会有错误，可以忽略，那是因为检测别的节点的时候连接失败导致，生产环境可以针对具体情况忽略此类错误。

• 然后依次启动ZKClient1，ZKClient2和ZKClient3。

• 分别观察三个Client日志输出。

• 停止当前选举到的leader，比如ZKClient1，然后观察日志输出，一段时间后会重新选举出一个leader。

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