Eureka 的 Application Client client的執行示範範例

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        上篇以一個 demo 示範範例介紹了 Eureka 的 Application Service 用戶端角色。今天我們繼續瞭解 Eureka 的 Application Client 用戶端，以一個簡單的互動示範範例，介紹 Application Client 是怎樣使用 Eureka 擷取 Application Service 執行個體並發送請求的。
        上篇《Eureka 的 Application Service 用戶端的注冊以及執行示範範例》使用了一個 Socket 服務做為 demo，本文示範範例配合該文，將以一個 Socket 用戶端對該服務進行請求。
        1. Eureka 伺服器啟動
        本文 demo 要求 Eureka Server 已經部署好，並已經啟動。關於架設步驟參考部落格《Linux 下 Eureka 伺服器的部署》。
        2. Application Service 服務啟動
        直接將《Eureka 的 Application Service 用戶端的注冊以及執行示範範例》中的小 demo 跑起來(Socket Server 啟動，開始侍服網路請求)。
        3. Application Client 設定檔的編寫
        我們的 Application Client 就用官方提供 demo 裡的 sampleclient 下的 sample-eureka-client.properties 就可以，當然還要依據實際情況修正一下，比方把 eureka.serviceUrl.default(預設情況下本用戶端將要注冊到的 Eureka 伺服器)：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-1eureka.region=default#Name of the application to be identified by other serviceseureka.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 zoneseureka.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.propertieseureka.shouldUseDns=falseeureka.us-east-1.availabilityZones=defaulteureka.serviceUrl.default=http://serverIP:8080/eureka/v2/

        4. 日誌配置
        就用官方提供 demo 裡的 sampleclient 下的 log4j.properties 就可以，當然還要依據實際須要修正一下，比方給 com.netflix.eureka 包的輸出層級設定為 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,stdoutlog4j.appender.stdout=org.apache.log4j.ConsoleAppenderlog4j.appender.stdout.layout=org.apache.log4j.PatternLayoutlog4j.appender.stdout.layout.ConversionPattern=%d %-5p %C:%L [%t] [%M] %m%nlog4j.logger.com.netflix.eureka=DEBUG

        5. 尋找本次請求的 Application Service 執行個體
        用戶端在向 Application Service 請求之前得先從 Eureka Server 拿到侍服本次請求的 Application Service 執行個體。尋找本次請求的 Application Service 執行個體的代碼例如以下：

        // 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);

        第一句初始化本用戶端，第二句告訴 Eureka 本用戶端處於就緒狀態，接下來兩句是使用 Eureka 找到對本次請求進行侍服的 Application Service 執行個體。
        6. Application Client 網路請求
        Application Client 拿到 Application Service之後立刻進行網路 Socket 請求，進行資料資訊互動。

        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 關閉時取消注冊
        Application Client 在關閉時要將自己在 Eureka 的注冊取消掉。

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

        8. 執行 demo
        建立一個項目(不要和 Application Service 的 demo 跑在同一個項目下)，如今我們把完整的 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();    }}

        如上篇部落格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 重新命名為 config.properties(原因參考上篇部落格)，接下來就能夠執行本文 demo 了。run SampleEurekaClient，日誌結果例如以下：
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: [email protected]
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 擷取 Application Service 執行個體並請求成功。
        能夠看出，Application Service 執行個體的資訊都封裝在了 com.netflix.appinfo.InstanceInfo 下，那麼我們還能從中擷取哪些資訊？SampleEurekaClient 類增加下面代碼：

        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());

        然後又一次執行本文 demo，以上語句列印結果例如以下：
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
        這些資訊都和 http://serverIP:8080/eureka/v2/apps/ 顯示的 SAMPLESERVICE 執行個體的 各個屬性一一相應。
        參考資料

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

Eureka 的 Application Client client的執行示範範例