Zookeeper应用 - 集中配置管理系统的实现

最近在工作中，为了完善公司集群服务的架构，提高可用性，降低运维成本，因此开始学习ZooKeeper。
    至于什么是ZooKeeper？它能做什么？如何安装ZooKeeper？我就不一一介绍了，类似这些资料网上到处都是。我主要是把在开发过程中，以及个人对ZooKeeper的一些了解记录下来，大家如果遇到类似场景时，希望我的文章能够给你提供一些思路。

    我使用的ZooKeeper（以下简称：ZK）客户端是Curator Framework，是Apache的项目，它主要的功能是为ZK的客户端使用提供了高可用的封装。在Curator Framework基础上封装的curator-recipes，实现了很多经典场景。比如：集群管理（Leader选举）、共享锁、队列、Counter等等。可以总结Curator主要解决以下三类问题：

• 封装ZK Client与Server之间的连接处理； 
• 提供了一套Fluent风格的操作API； 
• 提供ZK各种应用场景的抽象封装；

   本文主要完成的目标是：Spring PropertyPlaceholderConfigurer配置文件加载器集成ZooKeeper来实现远程配置读取。

    配置管理（Configuration Management）。
    在集群服务中，可能都会遇到一个问题：那就是当需要修改配置的时候，必须要对每个实例都进行修改，这是一个很繁琐的事情，并且易出错。当然可以使用脚本来解决，但这不是最好的解决办法。

OK，Let's go！

我们先看看项目结构

ZooKeeperPropertyPlaceholderConfigurer.java

继承org.springframework.beans.factory.config.PropertyPlaceholderConfigurer，重写processProperties(beanFactoryToProcess, props)来完成远端配置加载的实现

package org.bigmouth.common.zookeeper.config.spring;

import java.io.UnsupportedEncodingException;
import java.util.Properties;

import org.apache.commons.lang.StringUtils;
import org.bigmouth.common.zookeeper.config.Config;
import org.bigmouth.common.zookeeper.config.ZooKeeperConfig;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;


public class ZooKeeperPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {

    public static final String PATH = "zoo.paths" ;

    @Override
    protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
            throws BeansException {
        super .processProperties(beanFactoryToProcess, props);

        try {
            fillCustomProperties(props);

            System.out.println(props);
        }
        catch (Exception e) {
            // Ignore
            e.printStackTrace();
        }
    }

    private void fillCustomProperties(Properties props) throws Exception {
        byte [] data = getData(props);
        fillProperties(props, data);
    }

    private void fillProperties(Properties props, byte [] data) throws UnsupportedEncodingException {
        String cfg = new String(data, "UTF-8" );
        if (StringUtils.isNotBlank(cfg)) {
            // 完整的应该还需要处理：多条配置、value中包含=、忽略#号开头
            String[] cfgItem = StringUtils.split(cfg, "=" );
            props.put(cfgItem[ 0 ], cfgItem[ 1 ]);
        }
    }

    private byte [] getData(Properties props) throws Exception {
        String path = props.getProperty(PATH);
        Config config = new ZooKeeperConfig();
        return config.getConfig(path);
    }

}

Config.java
配置操作接口 

package org.bigmouth.common.zookeeper.config;


public interface Config {

    byte [] getConfig(String path) throws Exception;
}

Startup.java

程序启动入口

package org.bigmouth.common.zookeeper.config;

import org.springframework.context.support.ClassPathXmlApplicationContext;


public class Startup {

    public static void main(String[] args) {
        new ClassPathXmlApplicationContext( "classpath:/config/applicationContext.xml" );
    }

}

ZooKeeperConfig.java

配置操作接口ZooKeeper的实现

package org.bigmouth.common.zookeeper.config;

import org.apache.curator.framework.CuratorFramework;
import org.apache.zookeeper.data.Stat;


public class ZooKeeperConfig implements Config {

    @Override
    public byte [] getConfig(String path) throws Exception {
        CuratorFramework client = ZooKeeperFactory.get();
        if (!exists(client, path)) {
            throw new RuntimeException( "Path " + path + " does not exists." );
        }
        return client.getData().forPath(path);
    }

    private boolean exists(CuratorFramework client, String path) throws Exception {
        Stat stat = client.checkExists().forPath(path);
        return !(stat == null );
    }

}

ZooKeeperFactory.java

管理ZooKeeper客户端连接

package org.bigmouth.common.zookeeper.config;

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;

public class ZooKeeperFactory {

    public static final String CONNECT_STRING = "172.16.3.42:2181,172.16.3.65:2181,172.16.3.24:2181" ;

    public static final int MAX_RETRIES = 3 ;

    public static final int BASE_SLEEP_TIMEMS = 3000 ;

    public static final String NAME_SPACE = "cfg" ;

    public static CuratorFramework get() {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(BASE_SLEEP_TIMEMS, MAX_RETRIES);
        CuratorFramework client = CuratorFrameworkFactory.builder()
                .connectString(CONNECT_STRING)
                .retryPolicy(retryPolicy)
                .namespace(NAME_SPACE)
                .build();
        client.start();
        return client;
    }
}

applicationContext.xml

配置加载器使用我们自己创建的ZooKeeperPropertyPlaceholderConfigurer，因为它重写了processProperties方法。这个方法里会去读取远程配置。

<? xml version = "1.0" encoding = "UTF-8" ?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
< beans >

    < bean class = "org.bigmouth.common.zookeeper.config.spring.ZooKeeperPropertyPlaceholderConfigurer" >
        < property name = "systemPropertiesModeName" value = "SYSTEM_PROPERTIES_MODE_OVERRIDE" />
        < property name = "ignoreResourceNotFound" value = "true" />
        < property name = "locations" >
            < list >
                < value >classpath:application.properties</ value >
            </ list >
        </ property >
    </ bean >

</ beans >

application.properties

项目配置文件，里面除了配置ZooKeeper服务器地址和读取的节点以外，其他所有的配置都应该保存在ZooKeeper中。

zoo.paths=/properties

设置ZooKeeper数据

登录ZooKeeper中为节点 /cfg/properties 添加一条配置项：

如图所示：我创建了一个节点 /cfg/properties 并设置内容为：jdbc.driver=org.postgresql.Driver

运行Startup.java

OK 了，zoo.paths是本地application.properties文件中的，jdbc.driver是远程ZooKeeper服务器中的。

项目中需要依赖的jar包

< dependency >
    < groupId >commons-lang</ groupId >
    < artifactId >commons-lang</ artifactId >
    < version >2.4</ version >
</ dependency >
< dependency >
    < groupId >org.springframework</ groupId >
    < artifactId >spring-core</ artifactId >
    < version >3.0.3.RELEASE</ version >
</ dependency >
< dependency >
    < groupId >org.springframework</ groupId >
    < artifactId >spring-context</ artifactId >
    < version >3.0.3.RELEASE</ version >
</ dependency >
< dependency >
    < groupId >org.springframework</ groupId >
    < artifactId >spring-tx</ artifactId >
    < version >3.0.3.RELEASE</ version >
</ dependency >
< dependency >
    < groupId >org.springframework</ groupId >
    < artifactId >spring-context-support</ artifactId >
    < version >3.0.3.RELEASE</ version >
</ dependency >

<!-- ZooKeeper -->
< dependency >
    < groupId >org.apache.zookeeper</ groupId >
    < artifactId >zookeeper</ artifactId >
    < version >3.4.6</ version >
</ dependency >
< dependency >
    < groupId >org.apache.curator</ groupId >
    < artifactId >curator-framework</ artifactId >
    < version >2.4.2</ version >
</ dependency >
< dependency >
    < groupId >org.apache.curator</ groupId >
    < artifactId >curator-recipes</ artifactId >
    < version >2.4.2</ version >
</ dependency >