Eureka 的 Application Client client的执行演示样例

        上篇以一个 demo 演示样例介绍了 Eureka 的 Application Service 客户端角色。今天我们继续了解 Eureka 的 Application Client 客户端，以一个简单的交互演示样例，介绍 Application Client 是怎样使用 Eureka 获取 Application Service 实例并发送请求的。
        上篇《Eureka 的 Application Service 客户端的注冊以及执行演示样例》使用了一个 Socket 服务做为 demo，本文演示样例配合该文，将以一个 Socket 客户端对该服务进行请求。
        1. Eureka 服务器启动
        本文 demo 要求 Eureka Server 已经部署好，并已经启动。关于架设步骤參考博客《Linux 下 Eureka 服务器的部署》。
        2. Application Service 服务启动
        直接将《Eureka 的 Application Service 客户端的注冊以及执行演示样例》中的小 demo 跑起来(Socket Server 启动，開始侍服网络请求)。
        3. Application Client 配置文件的编写
        我们的 Application Client 就用官方提供 demo 里的 sampleclient 下的 sample-eureka-client.properties 就可以，当然还要依据实际情况修正一下，比方把 eureka.serviceUrl.default(默认情况下本客户端将要注冊到的 Eureka 服务器)：http://serverIP:8080/eureka/v2/：

###Eureka Client configuration for Sample Eureka Client

#Properties based configuration for eureka client. The properties specified here is mostly what the users
#need to change. All of these can be specified as a java system property with -D option (eg)-Deureka.region=us-east-1
#For additional tuning options refer <url to go here>

#Region where eureka is deployed -For AWS specify one of the AWS regions, for other datacenters specify a arbitrary string
#indicating the region.This is normally specified as a -D option (eg) -Deureka.region=us-east-1
eureka.region=default

#Name of the application to be identified by other services

eureka.name=sampleEurekaClient

#Virtual host name by which the clients identifies this service
#eureka.vipAddress=eureka.mydomain.net

#The port where the service will be running and servicing requests
#eureka.port=80

#For eureka clients running in eureka server, it needs to connect to servers in other zones
eureka.preferSameZone=true

#Change this if you want to use a DNS based lookup for determining other eureka servers. For example
#of specifying the DNS entries, check the eureka-client-test.properties, eureka-client-prod.properties
eureka.shouldUseDns=false

eureka.us-east-1.availabilityZones=default

eureka.serviceUrl.default=http://serverIP:8080/eureka/v2/

4. 日志配置
        就用官方提供 demo 里的 sampleclient 下的 log4j.properties 就可以，当然还要依据实际须要修正一下，比方给 com.netflix.eureka 包的输出级别设置为 DEBUG(log4j.properties 追加 log4j.logger.com.netflix.eureka=DEBUG)，以方便我们研发期跟踪调试。

log4j.rootCategory=INFO,stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %-5p %C:%L [%t] [%M] %m%n
log4j.logger.com.netflix.eureka=DEBUG

5. 寻找本次请求的 Application Service 实例
        客户端在向 Application Service 请求之前得先从 Eureka Server 拿到侍服本次请求的 Application Service 实例。寻找本次请求的 Application Service 实例的代码例如以下：

        // Register with Eureka
        DiscoveryManager.getInstance().initComponent(
                new MyDataCenterInstanceConfig(),
                new DefaultEurekaClientConfig());
        ApplicationInfoManager.getInstance().setInstanceStatus(
                InstanceStatus.UP);
        String vipAddress = configInstance.getStringProperty(
                "eureka.vipAddress", "sampleservice.mydomain.net").get();
        InstanceInfo nextServerInfo = DiscoveryManager.getInstance()
                .getDiscoveryClient()
                .getNextServerFromEureka(vipAddress, false);

第一句初始化本客户端，第二句告诉 Eureka 本客户端处于就绪状态，接下来两句是使用 Eureka 找到对本次请求进行侍服的 Application Service 实例。
        6. Application Client 网络请求
        Application Client 拿到 Application Service 之后立刻进行网络 Socket 请求，进行数据信息交互。

        Socket s = new Socket();
        int serverPort = nextServerInfo.getPort();
        try {
            s.connect(new InetSocketAddress(nextServerInfo.getHostName(),
                    serverPort));
        } catch (IOException e) {
            System.err.println("Could not connect to the server :"
                    + nextServerInfo.getHostName() + " at port " + serverPort);
        }
        try {
            System.out.println("Connected to server. Sending a sample request");
            PrintStream out = new PrintStream(s.getOutputStream());
            out.println("Sample request " + new Date());
            String str = null;
            System.out.println("Waiting for server response..");
            BufferedReader rd = new BufferedReader(new InputStreamReader(
                    s.getInputStream()));
            str = rd.readLine();
            if (str != null) {
                System.out
                        .println("Received response from server. Communication all fine using Eureka :");
                System.out.println("Exiting the client. Demo over..");
            }
            rd.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

7. Application Client 关闭时取消注冊
        Application Client 在关闭时要将自己在 Eureka 的注冊取消掉。

    public void unRegisterWithEureka() {
        // Un register from eureka.
        DiscoveryManager.getInstance().shutdownComponent();
    }

8. 执行 demo
        新建一个项目(不要和 Application Service 的 demo 跑在同一个项目下)，如今我们把完整的 Application Client 代码整理一下。

/*
 * Copyright 2012 Netflix, Inc.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

package com.netflix.eureka;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.Date;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.netflix.appinfo.ApplicationInfoManager;
import com.netflix.appinfo.InstanceInfo;
import com.netflix.appinfo.InstanceInfo.InstanceStatus;
import com.netflix.appinfo.MyDataCenterInstanceConfig;
import com.netflix.config.DynamicPropertyFactory;
import com.netflix.discovery.DefaultEurekaClientConfig;
import com.netflix.discovery.DiscoveryManager;

/**
 * Sample Eureka client that discovers the service using Eureka and sends
 * requests.
 *
 * @author Karthik Ranganathan
 *
 */
public class SampleEurekaClient {
    private static final DynamicPropertyFactory configInstance = com.netflix.config.DynamicPropertyFactory
            .getInstance();

    private static final Logger logger = LoggerFactory
    .getLogger(SampleEurekaClient.class);

    public void sendRequestToServiceUsingEureka() {
        // Register with Eureka
        DiscoveryManager.getInstance().initComponent(
                new MyDataCenterInstanceConfig(),
                new DefaultEurekaClientConfig());
        ApplicationInfoManager.getInstance().setInstanceStatus(
                InstanceStatus.UP);
        String vipAddress = configInstance.getStringProperty(
                "eureka.vipAddress", "sampleservice.mydomain.net").get();
        InstanceInfo nextServerInfo = DiscoveryManager.getInstance()
                .getDiscoveryClient()
                .getNextServerFromEureka(vipAddress, false);

        Socket s = new Socket();
        int serverPort = nextServerInfo.getPort();
        try {
            s.connect(new InetSocketAddress(nextServerInfo.getHostName(),
                    serverPort));
        } catch (IOException e) {
            System.err.println("Could not connect to the server :"
                    + nextServerInfo.getHostName() + " at port " + serverPort);
        }
        try {
            System.out.println("Connected to server. Sending a sample request");
            PrintStream out = new PrintStream(s.getOutputStream());
            out.println("Sample request " + new Date());
            String str = null;
            System.out.println("Waiting for server response..");
            BufferedReader rd = new BufferedReader(new InputStreamReader(
                    s.getInputStream()));
            str = rd.readLine();
            if (str != null) {
                System.out
                        .println("Received response from server. Communication all fine using Eureka :");
                System.out.println("Exiting the client. Demo over..");
            }
            rd.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        this.unRegisterWithEureka();
    }

    public void unRegisterWithEureka() {
        // Un register from eureka.
        DiscoveryManager.getInstance().shutdownComponent();
    }

    public static void main(String[] args) {
        SampleEurekaClient sampleEurekaService = new SampleEurekaClient();
        sampleEurekaService.sendRequestToServiceUsingEureka();

    }

}

如上篇博客所述一样把各种依赖包加进本文 demo 的 CLASSPATH，然后把第三、四步写好的 sample-eureka-client.properties、log4j.properties 也拷贝进 CLASSPATH，并将 sample-eureka-client.properties 重命名为 config.properties(原因參考上篇博客)，接下来就能够执行本文 demo 了。run SampleEurekaClient，日志结果例如以下：
2014-07-10 11:02:51,860 INFO  com.netflix.config.sources.URLConfigurationSource:125 [main] [<init>] URLs to be used as dynamic configuration source: [file:/D:/javaprojects/test2/bin/config.properties]
2014-07-10 11:02:51,927 INFO  com.netflix.config.DynamicPropertyFactory:281 [main] [getInstance] DynamicPropertyFactory is initialized with configuration sources: com.netflix.config.ConcurrentCompositeConfiguration@5ca46701
2014-07-10 11:02:52,060 WARN  com.netflix.appinfo.PropertiesInstanceConfig:349 [main] [init] Cannot find the properties specified : eureka-client. This may be okay if there are other environment specific properties or the configuration is installed with a different mechanism.
2014-07-10 11:02:52,065 WARN  com.netflix.discovery.DefaultEurekaClientConfig:95 [main] [init] Cannot find the properties specified : eureka-client. This may be okay if there are other environment specific properties or the configuration is installed with a different mechanism.
2014-07-10 11:02:52,103 INFO  com.netflix.appinfo.providers.EurekaConfigBasedInstanceInfoProvider:79 [main] [get] Setting initial instance status as: STARTING
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:646 [main] [fetchRegistry] Disable delta property : false
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:647 [main] [fetchRegistry] Single vip registry refresh property : null
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:648 [main] [fetchRegistry] Force full registry fetch : false
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:649 [main] [fetchRegistry] Application is null : false
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:650 [main] [fetchRegistry] Registered Applications size is zero : true
2014-07-10 11:02:53,668 INFO  com.netflix.discovery.DiscoveryClient:652 [main] [fetchRegistry] Application version is -1: true
2014-07-10 11:02:54,061 INFO  com.netflix.discovery.DiscoveryClient:992 [main] [makeRemoteCall] Finished a call to service url http://serverIP:8080/eureka/v2/ and url path apps/ with status code 200.
2014-07-10 11:02:54,061 INFO  com.netflix.discovery.DiscoveryClient:758 [main] [getAndStoreFullRegistry] Getting all instance registry info from the eureka server
2014-07-10 11:02:54,568 INFO  com.netflix.discovery.DiscoveryClient:765 [main] [getAndStoreFullRegistry] The response status is 200
2014-07-10 11:02:54,578 INFO  com.netflix.discovery.DiscoveryClient:1056 [main] [initScheduledTasks] Starting heartbeat executor: renew interval is: 30
Connected to server. Sending a sample request
Waiting for server response..
Received response from server. Communication all fine using Eureka :
Exiting the client. Demo over..
        证明 demo 获取 Application Service 实例并请求成功。
        能够看出，Application Service 实例的信息都封装在了 com.netflix.appinfo.InstanceInfo 下，那么我们还能从中获取哪些信息？SampleEurekaClient 类增加下面代码：

        logger.debug("nextServerInfo.getAppGroupName()-" + nextServerInfo.getAppGroupName());
        logger.debug("nextServerInfo.getAppName()-" + nextServerInfo.getAppName());
        logger.debug("nextServerInfo.getASGName()-" + nextServerInfo.getASGName());
        logger.debug("nextServerInfo.getHomePageUrl()-" + nextServerInfo.getHomePageUrl());
        logger.debug("nextServerInfo.getHostName()-" + nextServerInfo.getHostName());
        logger.debug("nextServerInfo.getId()-" + nextServerInfo.getId());
        logger.debug("nextServerInfo.getIPAddr()-" + nextServerInfo.getIPAddr());
        logger.debug("nextServerInfo.getLastUpdatedTimestamp()-" + nextServerInfo.getLastUpdatedTimestamp());
        logger.debug("nextServerInfo.getPort()-" + nextServerInfo.getPort());
        logger.debug("nextServerInfo.getSecureVipAddress()-" + nextServerInfo.getSecureVipAddress());
        logger.debug("nextServerInfo.getStatusPageUrl()-" + nextServerInfo.getStatusPageUrl());
        logger.debug("nextServerInfo.getVIPAddress()-" + nextServerInfo.getVIPAddress());
        logger.debug("nextServerInfo.getLastDirtyTimestamp()-" + nextServerInfo.getLastDirtyTimestamp());
        logger.debug("nextServerInfo.getHealthCheckUrls()-" + nextServerInfo.getHealthCheckUrls());
        logger.debug("nextServerInfo.getStatus()-" + nextServerInfo.getStatus());

然后又一次执行本文 demo，以上语句打印结果例如以下：
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:69 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getAppGroupName()-UNKNOWN
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:70 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getAppName()-SAMPLESERVICE
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:71 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getASGName()-null
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:72 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getHomePageUrl()-http://defonds-win7:1935/
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:73 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getHostName()-defonds-win7
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:74 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getId()-defonds-win7
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:75 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getIPAddr()-172.21.40.134
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:76 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getLastUpdatedTimestamp()-1404961202884
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:77 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getPort()-1935
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:78 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getSecureVipAddress()-null
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:79 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getStatusPageUrl()-http://defonds-win7:1935/Status
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:80 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getVIPAddress()-sampleservice.mydomain.net
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:81 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getLastDirtyTimestamp()-1404961230856
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:82 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getHealthCheckUrls()-[http://defonds-win7:1935/healthcheck]
2014-07-10 11:02:54,621 DEBUG com.netflix.eureka.SampleEurekaClient:83 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getStatus()-UP
        这些信息都和 http://serverIP:8080/eureka/v2/apps/ 显示的 SAMPLESERVICE 实例的 各个属性一一相应。
        參考资料

• https://github.com/Netflix/eureka/tree/master/eureka-server/conf