Zookeeper如何实现分布式服务配置中心详解
什么是Zookeeper
Zookeeper是一个典型的分布式数据一致性解决方案,是Google Chubby在开源领域的实现,提供了分布式应用系统的协调服务,如配置维护、命名服务、同步服务、组服务等。
Zookeeper作为服务配置中心的应用
服务配置中心是比较常用的分布式架构中的一部分,它的目的是帮助我们实现应用程序的配置管理。Zookeeper正是通过其节点、事件机制等特性来支持分布式服务的协调和应用配置的管理。
Zookeeper实现分布式服务配置中心
配置项的注册和发现
通过节点机制,Zookeeper实现了配置项的注册和发现。我们可以将配置项写入到Zookeeper的特定节点下,通过监控该节点路径实现节点值变化的监听,使配置变化得到及时的通知。应用程序在启动时可以对Zookeeper的节点路径进行监听,当Zookeeper节点的值变化时,可以及时获取变化的值。
下面通过Java程序示例说明:
- 注册配置项
public class ConfigCenter {
private ZooKeeper zooKeeper;
private static String CONFIG_ROOT_NODE_PATH = "/config-center";
private String configNodePath;
public ConfigCenter(String connectString, int sessionTimeout) throws IOException, KeeperException, InterruptedException {
this.zooKeeper = new ZooKeeper(connectString, sessionTimeout, null);
if (zooKeeper.exists(CONFIG_ROOT_NODE_PATH, false) == null) {
zooKeeper.create(CONFIG_ROOT_NODE_PATH, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
}
}
/**
* 注册配置项
* @param configName 配置项名称
* @param configValue 配置项值
* @return 配置项在Zookeeper中的节点路径
* @throws KeeperException
* @throws InterruptedException
*/
public String registerConfig(String configName, String configValue) throws KeeperException, InterruptedException {
configNodePath = zooKeeper.create(CONFIG_ROOT_NODE_PATH + "/" + configName, configValue.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
return configNodePath;
}
}
- 监听配置项变化
public class ConfigCenterWatcher implements Watcher {
private ZooKeeper zooKeeper;
private String configNodePath;
public ConfigCenterWatcher(ZooKeeper zooKeeper, String configNodePath) {
this.zooKeeper = zooKeeper;
this.configNodePath = configNodePath;
}
@Override
public void process(WatchedEvent event) {
switch (event.getType()) {
case NodeDataChanged:
try {
byte[] data = zooKeeper.getData(configNodePath, this, null);
System.out.println("配置项已经更新,新值为:" + new String(data));
} catch (KeeperException | InterruptedException e) {
e.printStackTrace();
}
break;
default:
break;
}
}
}
- 使用示例
public class ConfigCenterTest {
private static String CONNECT_STRING = "localhost:2181";
private static int SESSION_TIMEOUT = 10000;
private static String CONFIG_NAME = "testConfig";
private static String CONFIG_VALUE = "testConfigValue";
@Test
public void testConfigCenter() throws IOException, KeeperException, InterruptedException, InterruptedException {
ConfigCenter configCenter = new ConfigCenter(CONNECT_STRING, SESSION_TIMEOUT);
String configNodePath = configCenter.registerConfig(CONFIG_NAME, CONFIG_VALUE);
ZooKeeper zooKeeper = new ZooKeeper(CONNECT_STRING, SESSION_TIMEOUT, new ConfigCenterWatcher(zooKeeper, configNodePath));
byte[] data = zooKeeper.getData(configNodePath, true, null);
System.out.println("配置项初始值为:" + new String(data));
Thread.sleep(Long.MAX_VALUE);
}
}
该示例通过Zookeeper实现了配置项注册和变化时的通知。
分布式应用系统中的服务发现
Zookeeper可以帮助我们实现分布式应用系统中的服务发现。在分布式系统中,服务可用性监控和负载均衡都是必须的特性。Zookeeper作为注册中心能够协调分布式应用系统中的服务注册和发现,也就是说,实现了单台服务器到集群间的扩展,让分布式服务可以向Zookeeper注册自己的服务地址和相关信息,也可以从Zookeeper查询服务注册信息。
下面通过Java程序示例说明:
- 服务注册
public class ServerRegistry {
private ZooKeeper zooKeeper;
private static String SERVER_NODE_PATH = "/server";
public ServerRegistry(String connectString, int sessionTimeout) throws IOException, KeeperException, InterruptedException {
this.zooKeeper = new ZooKeeper(connectString, sessionTimeout, null);
if (zooKeeper.exists(SERVER_NODE_PATH, false) == null) {
zooKeeper.create(SERVER_NODE_PATH, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
}
}
/**
* 服务注册
* @param serverName 服务名
* @param serverAddress 服务地址
* @throws KeeperException
* @throws InterruptedException
*/
public void registerServer(String serverName, String serverAddress) throws KeeperException, InterruptedException {
String serverNodePath = SERVER_NODE_PATH + "/" + serverName;
if (zooKeeper.exists(serverNodePath, false) == null) {
zooKeeper.create(serverNodePath, serverAddress.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println(serverName + "已注册,地址为:" + serverAddress);
}
}
}
- 服务发现
public class LoadBalance {
private ZooKeeper zooKeeper;
private static String SERVER_NODE_PATH = "/server";
private String serviceName;
public LoadBalance(String connectString, int sessionTimeout, String serviceName) throws IOException, KeeperException, InterruptedException {
this.zooKeeper = new ZooKeeper(connectString, sessionTimeout, null);
if (zooKeeper.exists(SERVER_NODE_PATH, false) == null) {
throw new RuntimeException("no server to use");
}
this.serviceName = serviceName;
}
/**
* 选择服务器
* @return 服务器地址
* @throws KeeperException
* @throws InterruptedException
*/
public String selectServer() throws KeeperException, InterruptedException {
String serverNodePath = SERVER_NODE_PATH + "/" + serviceName;
List<String> servers = zooKeeper.getChildren(serverNodePath, true);
String serverAddress = null;
if (servers != null && servers.size() > 0) {
if (servers.size() == 1) {
serverAddress = new String(zooKeeper.getData(serverNodePath + "/" + servers.get(0), true, null));
System.out.println("唯一服务器地址为:" + serverAddress);
} else {
int index = ThreadLocalRandom.current().nextInt(servers.size());
serverAddress = new String(zooKeeper.getData(serverNodePath + "/" + servers.get(index), true, null));
System.out.println("随机选择的服务器地址为:" + serverAddress);
}
}
return serverAddress;
}
}
- 使用示例
public class ServerRegistryTest {
private static String CONNECT_STRING = "localhost:2181";
private static int SESSION_TIMEOUT = 10000;
private static String SERVER_NAME = "testServer";
private static String SERVER_ADDRESS_1 = "192.168.1.100:8080";
private static String SERVER_ADDRESS_2 = "192.168.1.101:8080";
private static String SERVICE_NAME = "testService";
@Test
public void testServerRegistry() throws IOException, KeeperException, InterruptedException {
ServerRegistry serverRegistry = new ServerRegistry(CONNECT_STRING, SESSION_TIMEOUT);
serverRegistry.registerServer(SERVER_NAME, SERVER_ADDRESS_1);
serverRegistry.registerServer(SERVER_NAME, SERVER_ADDRESS_2);
Thread.sleep(Long.MAX_VALUE);
}
@Test
public void testLoadBalance() throws IOException, KeeperException, InterruptedException {
LoadBalance loadBalance = new LoadBalance(CONNECT_STRING, SESSION_TIMEOUT, SERVICE_NAME);
while (true) {
try {
String serverAddress = loadBalance.selectServer();
System.out.println(serverAddress);
} catch (Exception e) {
System.out.println("no server to use");
Thread.sleep(2000);
}
}
}
}
这个示例通过Zookeeper实现了服务注册和发现,达到了负载均衡的效果。
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