Eureka 的 Application Client 客戶端的運行示例

上篇以一個 demo 示例介紹了 Eureka 的 Application Service 客戶端角色。今天我們繼續瞭解 Eureka 的 Application Client 客戶端，以一個簡單的交互示例，介紹 Application Client 是如何使用 Eureka 獲取 Application Service 實例併發送請求的。
        上篇《Eureka 的 Application Service 客戶端的註冊以及運行示例》使用了一個 Socket 服務做爲 demo，本文示例配合該文，將以一個 Socket 客戶端對該服務進行請求。
        1. Eureka 服務器啓動
        本文 demo 要求 Eureka Server 已經部署好，並已經啓動。關於架設步驟參考博客《Linux 下 Eureka 服務器的部署》。
        2. Application Service 服務啓動
        直接將《Eureka 的 Application Service 客戶端的註冊以及運行示例》中的小 demo 跑起來(Socket Server 啓動，開始侍服網絡請求)。
        3. Application Client 配置文件的編寫
        我們的 Application Client 就用官方提供 demo 裏的 sampleclient 下的 sample-eureka-client.properties 即可，當然還要根據實際情況修正一下，比如把 eureka.serviceUrl.default(默認情況下本客戶端將要註冊到的 Eureka 服務器)：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. 日誌配置
        就用官方提供 demo 裏的 sampleclient 下的 log4j.properties 即可，當然還要根據實際需要修正一下，比如給 com.netflix.eureka 包的輸出級別設置爲 DEBUG(log4j.properties 追加 log4j.logger.com.netflix.eureka=DEBUG)，以方便我們研發期跟蹤調試。

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. 尋找本次請求的 Application Service 實例
        客戶端在向 Application Service 請求之前得先從 Eureka Server 拿到侍服本次請求的 Application Service 實例。尋找本次請求的 Application Service 實例的代碼如下：

// 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);

        第一句初始化本客戶端，第二句告訴 Eureka 本客戶端處於就緒狀態，接下來兩句是使用 Eureka 找到對本次請求進行侍服的 Application Service 實例。
        6. Application Client 網絡請求
        Application Client 拿到 Application Service 之後立馬進行網絡 Socket 請求，進行數據信息交互。

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 關閉時取消註冊
        Application Client 在關閉時要將自己在 Eureka 的註冊取消掉。

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

        8. 運行 demo
        新建一個項目(不要和 Application Service 的 demo 跑在同一個項目下)，現在我們把完整的 Application Client 代碼整理一下。

/*
 * 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();


    }


}

        如上篇博客所述一樣把各種依賴包加進本文 demo 的 CLASSPATH，然後把第三、四步寫好的 sample-eureka-client.properties、log4j.properties 也拷貝進 CLASSPATH，並將 sample-eureka-client.properties 重命名爲 config.properties(原因參考上篇博客)，接下來就可以運行本文 demo 了。run SampleEurekaClient，日誌結果如下：
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..
        證明 demo 獲取 Application Service 實例並請求成功。
        可以看出，Application Service 實例的信息都封裝在了 com.netflix.appinfo.InstanceInfo 下，那麼我們還能從中獲取哪些信息？SampleEurekaClient 類加入以下代碼：

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());

        然後重新運行本文 demo，以上語句打印結果如下：
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
        這些信息都和 http://serverIP:8080/eureka/v2/apps/ 顯示的 SAMPLESERVICE 實例的 各個屬性一一對應。
        參考資料

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