zookeeper负载均衡

一 负载均衡原理

负载均衡为将应用的并发处理能力分摊到不同的机器中 机器上水平分布着相同功能的应用，实现负载均衡需要考虑到服务器的容灾能力，服务器的动态配置等

实现场景：

   假设在服务端存在一个webservice  部署在58.131，58.132上 客户端每次访问压力最小的服务器

   从零开发 需要当服务器58.131和58.132启动时 要在zookooper集群中注册临时节点   客户端订阅zookeeper该临时节点 客户端使用负载均衡算法 当访问服务器开始时 修改zookeeper上该服务器节点的值累加1  完成访问后 减1实现相对复杂

  

 Alibaba的dubbo框架实现了在zokeeper自动注册服务器 客户端自动订阅和缓存数据 以及负载均衡算法的功能 这里使用maven来添加dubbo和webservice依赖  dubbo必须依靠spring来进行管理

服务端代码

webservice接口

package cn.et.dubbo;public interface DemoService {public String sayHello(String name);}

实现类

 package cn.et.dubbo;public class DemoServiceImpl implements DemoService {public String sayHello(String name) {        return "Hello " + name;    } }

Spring配置文件

<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"xsi:schemaLocation="    http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd    http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd    "><!-- 提供方应用信息，用于计算依赖关系 name就是项目名称 --><dubbo:application name="uuid" /><!--注册服务器 当该服务启动时 自动将服务器信息写入 zookeeper服务器中    如果是zookeeper集群 address用逗号隔开-->    <dubbo:registry address="192.168.58.1:2181"  protocol="zookeeper" session="5000" timeout="1">    </dubbo:registry>    <!-- port和tomcat的端口必须一致  web.xml配置的servlet拦截的/*       访问都中http://当前ip:8080/上下文路径/cn.et.dubbo.DemoService?wsdl     -->    <dubbo:protocol name="webservice" port="8080" server="servlet" /><!-- 声明需要暴露的服务接口 --><dubbo:service interface="cn.et.dubbo.DemoService"  protocol="webservice" ref="demoService"  />    <bean id="demoService" class="cn.et.dubbo.DemoServiceImpl"></bean>    </beans>

Web.xml配置

       <context-param><param-name>contextConfigLocation</param-name><param-value>classpath:/spring.xml</param-value>       </context-param>        <!--spring的配置--><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener><servlet><servlet-name>dubbo</servlet-name><servlet-class>com.alibaba.dubbo.remoting.http.servlet.DispatcherServlet</servlet-class><load-on-startup>1</load-on-startup></servlet><servlet-mapping><servlet-name>dubbo</servlet-name><url-pattern>/*</url-pattern></servlet-mapping>

maven添加依赖

                <dependency><groupId>org.springframework</groupId><artifactId>spring-webmvc</artifactId><version>4.0.0.RELEASE</version></dependency><dependency><groupId>com.alibaba</groupId><artifactId>dubbo</artifactId><version>2.4.7</version><exclusions><exclusion><artifactId>spring</artifactId><groupId>org.springframework</groupId></exclusion></exclusions></dependency><dependency><groupId>org.apache.cxf</groupId><artifactId>cxf-rt-frontend-simple</artifactId><version>2.6.1</version></dependency><dependency><groupId>org.apache.cxf</groupId><artifactId>cxf-rt-transports-http</artifactId><version>2.6.1</version></dependency><dependency><groupId>org.eclipse.jetty</groupId><artifactId>jetty-server</artifactId><version>9.3.0.M2</version></dependency><dependency><groupId>com.github.sgroschupf</groupId><artifactId>zkclient</artifactId><version>0.1</version></dependency>

以上程序部署到 58.131,58.132的tomcat中 运行zkcli查看 /duddo节点下的子节点信息

有时 在linux启动时会抛出异常 bogon: bogon: Name or service not known, dubbo version: 2.4.7, current host:

 因为dubbo尝试获取linux主机名后获取对应的主机ip

 使用命令 hostname查看 主机名 为bogon

修改 /etc/hosts添加一行

 bogon 当前主机的ip

比如 58.131机器上添加 bogon 192.168.58.131

启动后 访问 

     http://192.168.58.131:8080/uuid/cn.et.dubbo.DemoService?wsdl

     http://192.168.58.132:8080/uuid/cn.et.dubbo.DemoService?wsdl

使用zkcli客户端查看zookeeper注册中心注册信息

[zk: 192.168.58.1:2181(CONNECTED) 258] ls /dubbo/cn.et.dubbo.DemoService/providers
[webservice%3A%2F%2F192.168.58.132%3A8080%2Fcn.et.dubbo.DemoService%3Fanyhost%3D
true%26application%3Duuid%26dubbo%3D2.4.7%26interface%3Dcn.et.dubbo.DemoService%
26methods%3DsayHello%26pid%3D4664%26server%3Dservlet%26side%3Dprovider%26timesta
mp%3D1495539889340, webservice%3A%2F%2F192.168.58.131%3A8080%2Fcn.et.dubbo.DemoS
ervice%3Fanyhost%3Dtrue%26application%3Duuid%26dubbo%3D2.4.7%26interface%3Dcn.et
.dubbo.DemoService%26methods%3DsayHello%26pid%3D4494%26server%3Dservlet%26side%3
Dprovider%26timestamp%3D1495539894062]
[zk: localhost:2181(CONNECTED) 259]

【注意点1】

    <dubbo:registry address="192.168.58.1:2181" protocol="zookeeper" session="5000" timeout="1">

    这里设置的session超时时间和连接timeout 都是无效的 需要自己重写部分api 

 在dubbojar包 dubbo/internal/com.alibaba.dubbo.remoting.zookeeper.ZookeeperTrasporter资源文件 里面定义了 使用不同客户端调用zookeer的代码 

    里面有使用zkclient和curator的代码

   zkclient=com.alibaba.dubbo.remoting.zookeeper.zkclient.ZkclientZookeeperTransporter

  我们在自己的项目中新建一个相同的类 代码 拷贝相同

 

package cn.et.dubbo;import com.alibaba.dubbo.common.URL;import com.alibaba.dubbo.remoting.zookeeper.ZookeeperClient;import com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter;public class ZkclientZookeeperTransporter implements ZookeeperTransporter {public ZookeeperClient connect(URL url) {return new ZkclientZookeeperClient(url);}}

重写  ZkclientZookeeperClient类

package cn.et.dubbo;import java.util.List;import org.I0Itec.zkclient.IZkChildListener;import org.I0Itec.zkclient.IZkStateListener;import org.I0Itec.zkclient.ZkClient;import org.I0Itec.zkclient.exception.ZkNoNodeException;import org.I0Itec.zkclient.exception.ZkNodeExistsException;import org.apache.zookeeper.Watcher.Event.KeeperState;import com.alibaba.dubbo.common.URL;import com.alibaba.dubbo.remoting.zookeeper.ChildListener;import com.alibaba.dubbo.remoting.zookeeper.StateListener;import com.alibaba.dubbo.remoting.zookeeper.support.AbstractZookeeperClient;public class ZkclientZookeeperClient  extends AbstractZookeeperClient<IZkChildListener>  {private final ZkClient client;private volatile KeeperState state = KeeperState.SyncConnected;public ZkclientZookeeperClient(URL url) {super(url);

                //默认的代码是client = new ZkClient(url.getBackupAddress())client = new ZkClient(url.getBackupAddress(),5000,1000);//这里自己设置这个超时和连接时间client.subscribeStateChanges(new IZkStateListener() {public void handleStateChanged(KeeperState state) throws Exception {ZkclientZookeeperClient.this.state = state;if (state == KeeperState.Disconnected) {stateChanged(StateListener.DISCONNECTED);} else if (state == KeeperState.SyncConnected) {stateChanged(StateListener.CONNECTED);}}public void handleNewSession() throws Exception {stateChanged(StateListener.RECONNECTED);}});}public void createPersistent(String path) {try {client.createPersistent(path, true);} catch (ZkNodeExistsException e) {}}public void createEphemeral(String path) {try {/*这里  %2F为 /  重写添加上下文路径  也就是/cn.et.dubbo.DemoService 替换为 /uuid/cn.et.dubbo.DemoService订阅者 从 zookeeper中获取可以访问的服务器webservice地址  注册时不会添加上下文路径 所以我们需要添加上下文路径 才能正常调用如果在提供者 spring.xml中添加 <dubbo:protocol name="webservice" port="8080" server="servlet" path="uuid"/>dubbo在上下文路径后在加上一层 uuid访问编程了 http://localhost:8080/uuid/uuid/cn.et.dubbo.DemoService?wsdl * */if(path.indexOf("%2Fcn.et.dubbo.DemoService")>0){path=path.replaceAll("%2Fcn.et.dubbo.DemoService", "%2Fuuid%2Fcn.et.dubbo.DemoService");}client.createEphemeral(path);} catch (ZkNodeExistsException e) {}}public void delete(String path) {try {client.delete(path);} catch (ZkNoNodeException e) {}}public List<String> getChildren(String path) {try {return client.getChildren(path);        } catch (ZkNoNodeException e) {            return null;        }}public boolean isConnected() {return state == KeeperState.SyncConnected;}public void doClose() {client.close();}public IZkChildListener createTargetChildListener(String path, final ChildListener listener) {return new IZkChildListener() {public void handleChildChange(String parentPath, List<String> currentChilds)throws Exception {listener.childChanged(parentPath, currentChilds);}};}public List<String> addTargetChildListener(String path, final IZkChildListener listener) {return client.subscribeChildChanges(path, listener);}public void removeTargetChildListener(String path, IZkChildListener listener) {client.unsubscribeChildChanges(path,  listener);}}

修改完成将编译好的类 添加到jar包中 修改jar包中dubbo/internal/com.alibaba.dubbo.remoting.zookeeper.ZookeeperTrasporter文件

  zkclient=cn.et.dubbo。ZkclientZookeeperTransporter

【注意点2】实际访问地址为192.168.58.132:8080//uuid/cn.et.dubbo.DemoService?wsdl 前面带了上下文路径 

zookeeper中注册的确实192.168.58.132:8080/cn.et.dubbo.DemoService  订阅者（客户端） 获取这个地址肯定无法调用 （上面ZkclientZookeeperClient类

createEphemeral标红的部分就解决了 上下文路径注册的问题

）

客户端调用的配置 

spring.xml  

<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"xsi:schemaLocation="    http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd    http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd    "><!-- 提供方应用信息，用于计算依赖关系 --><dubbo:application name="uuid" />    <dubbo:registry address="192.168.58.1:2181"  protocol="zookeeper" session="5000" timeout="1" >    </dubbo:registry><!-- 声明需要暴露的服务接口 --><dubbo:reference interface="cn.et.dubbo.DemoService" id="mydemo"  ></dubbo:reference>    </beans>

pom.xml 依赖和服务器端一致

java调用代码

package cn.et.dubbo;import org.springframework.context.support.ClassPathXmlApplicationContext;public class Provider {/** *时间：2017-5-25 下午08:20:17 *作者： LM *联系方式：[e-mail] * @param args */public static void main(String[] args) throws Exception {        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(new String[] {"/spring.xml"});        DemoService demo=(DemoService)context.getBean("mydemo");        System.out.println(demo.sayHello("jiaozi"));        System.in.read(); // 按任意键退出    }}

此时交换停止 58.131和 58.132 运行客户端main方法 测试webservice是否能够调用 我这里正常调用