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：973465719@qq.com
	 * @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