zookeeper学习总结

一、集群部署：

zookeeper集群部署建议为奇数台机器（比如3台，5台），这样做是为了方便Parxos算法选举出leader节点和follower节点；

现在假设有三台centerOS7的机器，IP分别为：10.103.16.207, 10.103.16.208, 10.103.16.209，现在分别在这三台机器上部署上zookeeper环境，步骤如下：

1、配置JDK环境：这个就不用多说了；

2、下载zookeeper包：

到https://archive.apache.org/dist/zookeeper/ 下载zookeeper的包文件，我这里下载的是3.4.10版本；

3、解压文件：

tar -zxvf zookeeper-3.4.10.tar.gz -C /usr/local/zookeeper

4、修改配置；

cd /usr/local/zookeeper/conf

cp zoo_sample.cfg zoo.cfg

vim zoo.cfg

在其中增加下面内容（如果项目已经存在则替换就行）：

dataDir=/usr/local/zookeeper/data

dataLogDir=/usr/local/zookeeper/logs

server.1=10.103.16.207:2888:3888

server.2=10.103.16.208:2888:3888

server.3=10.103.16.209:2888:3888

在zookeeper下建立目录：

mkdir data

mkdir logs

切换到data目录下，生成myid文件：

echo “1” >> /usr/local/zookeeper/data/myid

三台机器分别指定对应的ID，如果10.103.16.207上的ID为1，10.103.16.208上的ID为2，10.103.16.209上的ID为3；

5、启动zookeeper；

cd /usr/local/zookeeper/bin

./zkServer.sh start

启动后通过命令 ./zkServer.sh status能查看启动是否成功，该节点是leader还是follower；

通过jps命令，如果能看到一个QuorumPeerMain的进程，说明zookeeper进程启动起来了；

6、使用工具操作zookeeper；

cd /usr/local/zookeeper/bin

连接zookeeper：./zkCli.sh 或者 ./zkCli.sh 10.103.16.208:2181；连接成功后就可以进行下面的操作；

查看节点信息：ls / 或者 ls /zookeeper（/zookeeper必须为已经存在的节点）；

创建节点：create /zookeeper/subnode “this is sub node data”

查看节点内容：get /zookeeper/subnode

设置节点内容：set /zookeeper/subnode “change node data”

删除节点：delete /zookeeper/subnode

查看命令行帮助：help

退出cli工具：quit

二、Zookeeper API 使用：

1、导入jar包；

<dependency><groupId>org.apache.zookeeper</groupId><artifactId>zookeeper</artifactId><version>3.4.5</version>
</dependency>

2、编写服务端：

 1 public class Server {
 2     private static final String connectString = "10.103.16.207:2181";
 3     private static final int sessionTimeout = 2000;
 4     private static final String parentNode = "/zookeeper";
 5     private ZooKeeper zk = null;
 6     private static final String hostname = "10.103.16.214";
 7
 8     /**
 9      * 创建到zk的客户端连接
10      */
11     public void getConnect() throws Exception {
12         zk = new ZooKeeper(connectString, sessionTimeout, null);
13     }
14
15     /**
16      * 向zk集群注册服务器信息
17      */
18     public void registerServer(String hostname) throws Exception {
19         String create = zk.create(parentNode + "/server", hostname.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
20         System.out.println(hostname + "  is online.." + create);
21     }
22
23     /**
24      * 业务功能
25      *
26      * @throws InterruptedException
27      */
28     public void handleBussiness(String hostname) throws InterruptedException {
29         System.out.println(hostname + "  start working.....");
30         Thread.sleep(Long.MAX_VALUE);
31     }
32
33     public static void main(String[] args) throws Exception {
34         // 获取zk连接
35         Server server = new Server();
36         server.getConnect();
37         // 利用zk连接注册服务器信息
38         server.registerServer(hostname);
39         // 启动业务功能
40         server.handleBussiness(hostname);
41     }
42 }

3、编写客户端：

 1 public class Client implements Watcher {
 2     private static final String connectString = "10.103.16.207:2181";
 3     private static final int sessionTimeout = 2000;
 4     private static final String parentNode = "/zookeeper";
 5     private volatile List<String> serverList;
 6     private ZooKeeper zk = null;
 7
 8     @Override
 9     public void process(WatchedEvent event) {
10         System.out.println(event.getType() + "-------->"  + event.getPath());
11
12         try {
13             getServerList();
14         } catch (Exception e) {
15             e.printStackTrace();
16         }
17     }
18
19     /**
20      * 创建到zk的客户端连接
21      */
22     public void getConnect() throws Exception {
23         zk = new ZooKeeper(connectString, sessionTimeout, this);
24     }
25
26     /**
27      * 获取服务器信息列表
28      */
29     public void getServerList() throws Exception {
30         // 获取服务器子节点信息，并且对父节点进行监听
31         List<String> children = zk.getChildren(parentNode, true);
32         System.out.println(children);
33     }
34
35     /**
36      * 业务功能
37      */
38     public void handleBussiness() throws InterruptedException {
39         System.out.println("client start working.....");
40         Thread.sleep(Long.MAX_VALUE);
41     }
42
43     public static void main(String[] args) throws Exception {
44         // 获取zk连接
45         Client client = new Client();
46         client.getConnect();
47         // 业务线程启动
48         client.handleBussiness();
49     }
50 }

需要注意的是zookeeper API这里有个Bug，每次watcher执行后就自动失效了，需要重新绑定watcher一次，而在这个demo中，通过调用zk.getChildren时watch参数传入true来再次绑定（或者调用其他需要传入boolean watch参数的方法来绑定watcher）；

三、zkClient使用：

导入jar包；

1 <dependency>
2   <groupId>com.github.sgroschupf</groupId>
3   <artifactId>zkclient</artifactId>
4   <version>0.1</version>
5 </dependency>

编写服务端：

 1 public class Server {
 2     private static final String connectString = "10.103.16.207:2181,10.103.16.208:2181,10.103.16.209:2181";
 3     private static final int sessionTimeout = 2000;
 4     private static final String parentNode = "/zookeeper";
 5     private ZkClient zkClient = null;
 6
 7     private static final String hostname = "10.103.16.214";
 8
 9     public void getConnect() {
10         zkClient = new ZkClient(connectString);
11     }
12
13     public void registerServer(String hostname) {
14         String create = zkClient.create(parentNode + "/child", "hello, child node", CreateMode.EPHEMERAL_SEQUENTIAL);
15         System.out.println(hostname + "  is online.." + create);
16     }
17
18     public void handleBusiness(String hostname) throws InterruptedException {
19         System.out.println(hostname + "  start working.....");
20         Thread.sleep(Long.MAX_VALUE);
21     }
22
23     public static void main(String[] args) throws InterruptedException {
24         // 获取zk连接
25         Server server = new Server();
26         server.getConnect();
27         // 利用zk连接注册服务器信息
28         server.registerServer(hostname);
29         // 启动业务功能
30         server.handleBusiness(hostname);
31     }
32 }

编写客户端：

 1 public class Client implements IZkChildListener, IZkDataListener, IZkStateListener {
 2     private static final String connectString = "10.103.16.207:2181,10.103.16.208:2181,10.103.16.209:2181";
 3     private static final int sessionTimeout = 2000;
 4     private static final String parentNode = "/zookeeper";
 5     private volatile List<String> serverList;
 6
 7     private static ZkClient zkClient = null;
 8
 9     @Override
10     public void handleChildChange(String parentPath, List<String> currentChilds) throws Exception {
11         System.out.println("-----------child change: " + parentPath + "         " + currentChilds);
12     }
13
14     @Override
15     public void handleDataChange(String dataPath, Object data) throws Exception {
16         System.out.println("-----------data change: " + dataPath + "           " + data);
17     }
18
19     @Override
20     public void handleDataDeleted(String dataPath) throws Exception {
21         System.out.println("-----------data delete: " + dataPath);
22     }
23
24     @Override
25     public void handleStateChanged(Watcher.Event.KeeperState state) throws Exception {
26         System.out.println("-----------state change: " + state);
27     }
28
29     @Override
30     public void handleNewSession() throws Exception {
31         System.out.println("-----------new session***********");
32     }
33
34     public void getConnect() {
35         zkClient = new ZkClient(connectString);
36
37         zkClient.subscribeChildChanges(parentNode, this);
38         zkClient.subscribeDataChanges(parentNode, this);
39         zkClient.subscribeStateChanges(this);
40
41     }
42
43     public void handleBussiness() throws InterruptedException {
44         System.out.println("client start working.....");
45         Thread.sleep(Long.MAX_VALUE);
46     }
47
48     public static void main(String[] args) throws InterruptedException {
49         // 获取zk连接
50         Client client = new Client();
51         client.getConnect();
52         // 业务线程启动
53         client.handleBussiness();
54     }
55 }

四、Curator使用：

导入jar包；

1 <dependency>
2   <groupId>org.apache.curator</groupId>
3   <artifactId>curator-recipes</artifactId>
4   <version>2.7.0</version>
5 </dependency>

编写服务端：

 1 public class Server1 {
 2     private static final String connectString = "10.103.16.207:2181,10.103.16.208:2181,10.103.16.209:2181";
 3     private static final int sessionTimeout = 2000;
 4     private static final String parentNode = "/zookeeper";
 5     private CuratorFramework client = null;
 6
 7     private static final String hostname = "10.103.16.214";
 8
 9     public void getConnect() {
10         client = CuratorFrameworkFactory.newClient(
11                 connectString,
12                 new RetryNTimes(10, 5000)
13         );
14         client.start();
15     }
16
17     public void registerServer(String hostname) throws Exception {
18         PersistentEphemeralNode node = new PersistentEphemeralNode(client, PersistentEphemeralNode.Mode.EPHEMERAL,
19                 parentNode + "/" + hostname, "临时节点".getBytes());
20         node.start();
21     }
22
23     public void handleBusiness(String hostname) throws InterruptedException {
24         System.out.println(hostname + "  start working.....");
25         Thread.sleep(Long.MAX_VALUE);
26     }
27
28     public static void main(String[] args) throws Exception {
29         // 获取zk连接
30         Server1 server = new Server1();
31         server.getConnect();
32         // 利用zk连接注册服务器信息
33         server.registerServer(hostname);
34         // 启动业务功能
35         server.handleBusiness(hostname);
36     }
37 }

编写客户端：

 1 public class Client1 {
 2     private static final String connectString = "10.103.16.207:2181,10.103.16.208:2181,10.103.16.209:2181";
 3     private static final int sessionTimeout = 2000;
 4     private static final String parentNode = "/zookeeper";
 5     private CuratorFramework client = null;
 6
 7     private static final String hostname = "10.103.16.214";
 8
 9     public void getConnect() {
10         client = CuratorFrameworkFactory.newClient(
11                 connectString,
12                 new RetryNTimes(10, 5000)
13         );
14         client.start();
15     }
16
17     public void registerServer(String hostname) throws Exception {
18         TreeCache watcher = new TreeCache(client,  parentNode + "/" + hostname);
19         watcher.getListenable().addListener((client1, event) -> {
20             ChildData data = event.getData();
21             if (data == null) {
22                 System.out.println("No data in event[" + event + "]");
23             } else {
24                 System.out.println("Receive event: "
25                         + "type=[" + event.getType() + "]"
26                         + ", path=[" + data.getPath() + "]"
27                         + ", data=[" + new String(data.getData()) + "]"
28                         + ", stat=[" + data.getStat() + "]");
29             }
30         });
31         watcher.start();
32     }
33
34     public void handleBusiness(String hostname) throws InterruptedException {
35         System.out.println(hostname + "  start working.....");
36         Thread.sleep(Long.MAX_VALUE);
37     }
38
39     public static void main(String[] args) throws Exception {
40         // 获取zk连接
41         Client1 client = new Client1();
42         client.getConnect();
43         // 利用zk连接注册服务器信息
44         client.registerServer(hostname);
45         // 启动业务功能
46         client.handleBusiness(hostname);
47     }
48 }

五、常见问题：

1、集群部署时，配置好各节点参数后，启动zookeeper总是失败：

在BIN目录下有一个zookeeper.out文件记录了zookeeper启动中的日志，通过查看这个日志可以看到在连接其他节点时失败导致的报错，在确定网络没有问题的情况下，就应该是防火墙的原因导致的，只需要关闭掉防火墙就可以了；

在centerOS7下关闭防火墙：

systemctl stop firewalld.service；

在centerOS7下禁止掉防火墙（下次重启系统时也不再启动防火墙）：

systemctl disable firewalld.service；

2、连接zookeeper太久的问题：启动ZK后查看启动状态需要好久才能看到是leader还是follwer，java中使用API连接时卡住比较长时间或者有时经常连接失败的问题：

这个应该是系统的host解析问题导致的，在centerOS7系统中，编辑hosts文件（vim /etc/hosts），删掉127.0.0.1的那一行，重启网卡（/etc/rc.d/init.d/network restart），再次启动zookeeper即可发现连接快了很多；

六、参考资料：

书籍：《从PAXOS到ZOOKEEPER分布式一致性原理与实践》；
https://blog.csdn.net/shuxing520/article/details/79988167

　　　　https://blog.csdn.net/u012152619/article/category/6470028

　　　　https://blog.csdn.net/u012152619/article/details/53053634

　　　　https://www.cnblogs.com/leesf456/p/6036548.html

　　　　https://www.jianshu.com/p/24dbc4e7cc0d

　　　　https://blog.csdn.net/Regan_Hoo/article/details/78773817

　　　　https://blog.csdn.net/gs80140/article/details/51496925

Curator资料：

　　　　https://www.cnblogs.com/seaspring/p/5536338.html
　　　　https://blog.csdn.net/qq_15370821/article/details/73692288
　　　　https://www.cnblogs.com/sigm/p/6749228.html

转载于:https://www.cnblogs.com/laoxia/p/9585886.html