【一起学源码-微服务】Nexflix Eureka 源码五：EurekaClient启动要经历哪些艰难险阻？
前言
在源码分析三、四都有提及到EurekaClient启动的一些过程。因为EurekaServer在集群模式下 自己本身就是一个client，所以之前初始化eurekaServerContext就有涉及到eurekaClient的初始化。
我们也看了EurekaClient（DiscoveryClient）初始化的过程，繁杂的启动过程让人眼花缭乱，这篇文章就专门来唠唠 里面经历的一些艰难险阻。这也会是后面client注册的一个前置文章。
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从ExampleEurekaClient开始说起
在第一讲我们就说过，eureka项目有一个examples模块的，现在看一下其中的EurekaClientExample对象：
public class ExampleEurekaClient {
private static ApplicationInfoManager applicationInfoManager;
private static EurekaClient eurekaClient;
private static synchronized ApplicationInfoManager initializeApplicationInfoManager(EurekaInstanceConfig instanceConfig) {
if (applicationInfoManager == null) {
InstanceInfo instanceInfo = new EurekaConfigBasedInstanceInfoProvider(instanceConfig).get();
applicationInfoManager = new ApplicationInfoManager(instanceConfig, instanceInfo);
}
return applicationInfoManager;
}
private static synchronized EurekaClient initializeEurekaClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig clientConfig) {
if (eurekaClient == null) {
eurekaClient = new DiscoveryClient(applicationInfoManager, clientConfig);
}
return eurekaClient;
}
public void sendRequestToServiceUsingEureka(EurekaClient eurekaClient) {
// initialize the client
// this is the vip address for the example service to talk to as defined in conf/sample-eureka-service.properties
String vipAddress = "sampleservice.mydomain.net";
InstanceInfo nextServerInfo = null;
try {
nextServerInfo = eurekaClient.getNextServerFromEureka(vipAddress, false);
} catch (Exception e) {
System.err.println("Cannot get an instance of example service to talk to from eureka");
System.exit(-1);
}
System.out.println("Found an instance of example service to talk to from eureka: "
+ nextServerInfo.getVIPAddress() + ":" + nextServerInfo.getPort());
System.out.println("healthCheckUrl: " + nextServerInfo.getHealthCheckUrl());
System.out.println("override: " + nextServerInfo.getOverriddenStatus());
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);
} catch (Exception e) {
System.err.println("Could not connect to the server :"
+ nextServerInfo.getHostName() + " at port " + serverPort + "due to Exception " + e);
}
try {
String request = "FOO " + new Date();
System.out.println("Connected to server. Sending a sample request: " + request);
PrintStream out = new PrintStream(s.getOutputStream());
out.println(request);
System.out.println("Waiting for server response..");
BufferedReader rd = new BufferedReader(new InputStreamReader(s.getInputStream()));
String str = rd.readLine();
if (str != null) {
System.out.println("Received response from server: " + str);
System.out.println("Exiting the client. Demo over..");
}
rd.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws Exception{
injectEurekaConfiguration();
ExampleEurekaClient sampleClient = new ExampleEurekaClient();
// MyDataCenterInstanceConfig 就是加载eureka-client.properties配置信息,形成一个服务实例的配置EurekaInstanceConfig
// 基于EurekaClient配置，构造了一个服务实例（InstanceInfo）
// 基于eureka client配置和服务实例，构造了一个服务实例管理器（ApplicationInfoManager）
// 读取eureka-client.properties配置文件，形成了一个eureka client的配置，接口对外提供eureka client的配置项的读取
// 基于eureka client的配置，和服务实例管理器，来构造了一个EurekaClient（DiscoveryClient
// ），保存了一些配置，处理服务的注册和注册表的抓取，启动了几个线程池，启动了网络通信组件，启动了一些调度任务，注册了监控项
ApplicationInfoManager applicationInfoManager = initializeApplicationInfoManager(new MyDataCenterInstanceConfig());
EurekaClient client = initializeEurekaClient(applicationInfoManager, new DefaultEurekaClientConfig());
// use the client
sampleClient.sendRequestToServiceUsingEureka(client);
// shutdown the client
eurekaClient.shutdown();
}
/**
* This will be read by server internal discovery client. We need to salience it.
*/
private static void injectEurekaConfiguration() throws UnknownHostException {
String myHostName = InetAddress.getLocalHost().getHostName();
String myServiceUrl = "http://" + myHostName + ":8080/v2/";
System.setProperty("eureka.region", "default");
System.setProperty("eureka.name", "eureka");
System.setProperty("eureka.vipAddress", "eureka.mydomain.net");
System.setProperty("eureka.port", "8080");
System.setProperty("eureka.preferSameZone", "false");
System.setProperty("eureka.shouldUseDns", "false");
System.setProperty("eureka.shouldFetchRegistry", "true");
System.setProperty("eureka.serviceUrl.defaultZone", myServiceUrl);
System.setProperty("eureka.serviceUrl.default.defaultZone", myServiceUrl);
System.setProperty("eureka.awsAccessId", "fake_aws_access_id");
System.setProperty("eureka.awsSecretKey", "fake_aws_secret_key");
System.setProperty("eureka.numberRegistrySyncRetries", "0");
}
}
这里我们从main函数开始看起：
- 注入eureka配置信息：
injectEurekaConfiguration(); - 读取eureka-client.properties配置文件，形成一个服务器实例的配置，基于接口对外提供实例的配置项读取
这里就是涉及到我么你之前讲解的DynamicPropertyFactory和ConfigurationManager,这里可以查看new MyDataCenterInstanceConfig()然后一步步往后跟。 - 基于服务实例的配置，构造了一个服务实例（InstanceInfo）。
initializeApplicationInfoManager中会构建InstanceInfo信息 - 基于服务实例的配置和服务实例，初始化服务实例管理器（ApplicationInfoManager）
- 基于eureka client配置，和服务实例管理器，来构造了一个EurekaClient（DiscoveryClient），保存了一些配置，处理服务的注册和注册表的抓取，启动了几个线程池，启动了网络通信组件，启动了一些调度任务，注册了监控项
具体可查看EurekaClient client = initializeEurekaClient(applicationInfoManager, new DefaultEurekaClientConfig());
流程图
申明
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