启动eureka(源码解读二)

2022-05-28 20:59| 来源: 网络整理| 查看: 265

从github上把eureka的源码下载下来，按照readme进行build。

eureka是依赖tomcat的，server启动之后的界面是这样的：

这和我们用springboot集成eureka看到的界面很不一样，但是内容是大体相似的。

这个页面的源码在resources模块下：

它是用jsp写的，因为eureka出来的时间和Spring差不多。

在命令行运行：

./gradlew :eureka-examples:runExampleService

这里service注册和监听的逻辑在ExampleServiceBase.java这个类中：

@PostConstruct public void start() { // A good practice is to register as STARTING and only change status to UP // after the service is ready to receive traffic System.out.println("Registering service to eureka with STARTING status"); applicationInfoManager.setInstanceStatus(InstanceInfo.InstanceStatus.STARTING); System.out.println("Simulating service initialization by sleeping for 2 seconds..."); try { Thread.sleep(2000); } catch (InterruptedException e) { // Nothing } // Now we change our status to UP System.out.println("Done sleeping, now changing status to UP"); applicationInfoManager.setInstanceStatus(InstanceInfo.InstanceStatus.UP); waitForRegistrationWithEureka(eurekaClient); System.out.println("Service started and ready to process requests.."); try { int myServingPort = applicationInfoManager.getInfo().getPort(); // read from my registered info ServerSocket serverSocket = new ServerSocket(myServingPort); final Socket s = serverSocket.accept(); System.out.println("Client got connected... processing request from the client"); processRequest(s); } catch (IOException e) { e.printStackTrace(); } System.out.println("Simulating service doing work by sleeping for " + 5 + " seconds..."); try { Thread.sleep(5 * 1000); } catch (InterruptedException e) { // Nothing } }

它的流程是：

准备把service注册到eureka server，状态为STARTING睡两秒来模拟service的初始化，然后把状态改为UPwaitForRegistrationWithEureka(eurekaClient);将service注册到eureka server。 private void waitForRegistrationWithEureka(EurekaClient eurekaClient) { // my vip address to listen on String vipAddress = configInstance.getStringProperty("eureka.vipAddress", "sampleservice.mydomain.net").get(); InstanceInfo nextServerInfo = null; while (nextServerInfo == null) { try { nextServerInfo = eurekaClient.getNextServerFromEureka(vipAddress, false); } catch (Throwable e) { System.out.println("Waiting ... verifying service registration with eureka ..."); try { Thread.sleep(10000); } catch (InterruptedException e1) { e1.printStackTrace(); } } } }

这里用了一个死循环来将service注册到eureka server。

如何找这些server呢？用的是轮询（round-robin）：

@Override public InstanceInfo getNextServerFromEureka(String virtualHostname, boolean secure) { List instanceInfoList = this.getInstancesByVipAddress( virtualHostname, secure); if (instanceInfoList == null || instanceInfoList.isEmpty()) { throw new RuntimeException("No matches for the virtual host name :" + virtualHostname); } Applications apps = this.localRegionApps.get(); int index = (int) (apps.getNextIndex(virtualHostname, secure).incrementAndGet() % instanceInfoList.size()); return instanceInfoList.get(index); } 开一个ServerSocket监听连接： int myServingPort = applicationInfoManager.getInfo().getPort(); // read from my registered info ServerSocket serverSocket = new ServerSocket(myServingPort); final Socket s = serverSocket.accept();

于是service阻塞了：

运行./gradlew :eureka-examples:runExampleClient来启动client（消费者）。

它的逻辑在ExampleEurekaClient.java中：

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(); } }

通过写死的虚拟ip地址sampleservice.mydomain.net来找到euerka server。

然后连接：

Socket s = new Socket(); int serverPort = nextServerInfo.getPort(); try { s.connect(new InetSocketAddress(nextServerInfo.getHostName(), serverPort)); }

发数据：

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);

打印回复：

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.."); } 在service这端：

它会一个读取client发来的数据并且回一个时间。

private void processRequest(final Socket s) { try { BufferedReader rd = new BufferedReader(new InputStreamReader(s.getInputStream())); String line = rd.readLine(); if (line != null) { System.out.println("Received a request from the example client: " + line); } String response = "BAR " + new Date(); System.out.println("Sending the response to the client: " + response); PrintStream out = new PrintStream(s.getOutputStream()); out.println(response); } catch (Throwable e) { System.err.println("Error processing requests"); } finally { if (s != null) { try { s.close(); } catch (IOException e) { e.printStackTrace(); } } } }

以上就是eureka的大致逻辑，我们接下来会拆分细节解析。

如果你在启动service和client的时候报错了（也就是运行./gradlew :eureka-examples:runExampleService和./gradlew :eureka-examples:runExampleClient），可以invalidate cache和restart一下：

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