[Happy Qixi Festival] How does Nacos realize the service registration function?

《Java系核心技术》《中间件核心技术》
《微服务核心技术》《云原生核心技术》

today is a good day,祝大家七夕快乐.

many subscriptions 《微服务核心技术》 The readers of the column said in a private message in the background：看NacosNo idea when source code,In interviews, you are always asked for details.

Then in the next few days,Let's analyze it step by stepNacos的源码以及NacosThe core functions and mechanisms of,and proceed to write a registry,To help you better understand distributed middleware.

大家都知道Nacos有两大模块：注册中心和配置中心.

那么NacosHow to realize the service registration function of the registry?？我们来一探究竟.

在SpringBootunder the base,Whenever we introduce a new adaptation component,You should have a look under this component/META-INF/spring.factories文件,上一篇文章《注解@EnableAutoConfiguration的作用以及如何使用》提到,@SpringBootApplication会自动加载/META-INF/spring.factories文件.

跟进NacosServiceRegistryAutoConfiguration,This class is mainly to complete the service registration function, etc..

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnNacosDiscoveryEnabled
@ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled",
		matchIfMissing = true)
@AutoConfigureAfter({
     AutoServiceRegistrationConfiguration.class,
		AutoServiceRegistrationAutoConfiguration.class,
		NacosDiscoveryAutoConfiguration.class })
public class NacosServiceRegistryAutoConfiguration {
    

							...
							...
							...
	
	// service registry corebean
	@Bean
	@ConditionalOnBean(AutoServiceRegistrationProperties.class)
	public NacosAutoServiceRegistration nacosAutoServiceRegistration(
			NacosServiceRegistry registry,
			AutoServiceRegistrationProperties autoServiceRegistrationProperties,
			NacosRegistration registration) {
    
		return new NacosAutoServiceRegistration(registry,
				autoServiceRegistrationProperties, registration);
	}

}

跟进NacosAutoServiceRegistration

	public NacosAutoServiceRegistration(ServiceRegistry<Registration> serviceRegistry,
			AutoServiceRegistrationProperties autoServiceRegistrationProperties,
			NacosRegistration registration) {
    
		super(serviceRegistry, autoServiceRegistrationProperties);
		this.registration = registration;
	}

跟进super【AbstractAutoServiceRegistration】

	protected AbstractAutoServiceRegistration(ServiceRegistry<R> serviceRegistry,
			AutoServiceRegistrationProperties properties) {
    
		this.serviceRegistry = serviceRegistry;
		this.properties = properties;
	}

在这个类下,A monitoring method,This is the core of service registration method.

	@Override
	@SuppressWarnings("deprecation")
	public void onApplicationEvent(WebServerInitializedEvent event) {
    
		// The core method of service registration
		bind(event);
	}

Then there is a listening event,there should be a published event,So where is the event posted?？

事件是在WebServerStartStopLifecycle#start时发布的

springCore methods during container startup：finishRefresh(),Let's take a look at this method,算了,I'll write a special…移步《Spring源码之finishRefresh()》

SpringApplication#runCore method during startup：

1. finishRefresh()

2. getLifecycleProcessor().onRefresh();

WebServerStartStopLifecycle（实现SmartLifecycle接口）会发布 ServletWebServerInitializedEvent事件.

NacosAutoServiceRegistration的onApplicationEvent方法处理WebServerInitializedEvent事件.

	@Override
	public void start() {
    
		this.webServer.start();
		this.running = true;
		this.applicationContext
				.publishEvent(new ServletWebServerInitializedEvent(this.webServer, this.applicationContext));
	}

Know how it was released,我们来看一下AbstractAutoServiceRegistration#bind

	@Deprecated
	public void bind(WebServerInitializedEvent event) {
    
		ApplicationContext context = event.getApplicationContext();
		if (context instanceof ConfigurableWebServerApplicationContext) {
    
			if ("management".equals(((ConfigurableWebServerApplicationContext) context)
					.getServerNamespace())) {
    
				return;
			}
		}
		this.port.compareAndSet(0, event.getWebServer().getPort());
		// 跟进
		this.start();
	}

跟进this.start()

跟进register(),几经辗转,我们来到NacosServiceRegistry#register

跟进namingService.registerInstance(serviceId, group, instance);,我们来到NacosNamingService#registerInstance,我们重点关注一下

跟进NamingProxy#registerService,Assemble client information and send a request to the server.

由此可见,The request for service registration isPOST,请求路径是/nacos/v1/ns/instance

    public static String webContext = "/nacos";
    
    public static String nacosUrlBase = webContext + "/v1/ns";
    
    public static String nacosUrlInstance = nacosUrlBase + "/instance";

根据上述结论,We can find the correspondingAPI接口：InstanceController#register

    @CanDistro
    @PostMapping
    @Secured(action = ActionTypes.WRITE)
    public String register(HttpServletRequest request) throws Exception {
    
        
        final String namespaceId = WebUtils
                .optional(request, CommonParams.NAMESPACE_ID, Constants.DEFAULT_NAMESPACE_ID);
        final String serviceName = WebUtils.required(request, CommonParams.SERVICE_NAME);
        NamingUtils.checkServiceNameFormat(serviceName);
        
        final Instance instance = HttpRequestInstanceBuilder.newBuilder()
                .setDefaultInstanceEphemeral(switchDomain.isDefaultInstanceEphemeral()).setRequest(request).build();
        // 跟进
        getInstanceOperator().registerInstance(namespaceId, serviceName, instance);
        NotifyCenter.publishEvent(new RegisterInstanceTraceEvent(System.currentTimeMillis(), "",
                false, namespaceId, NamingUtils.getGroupName(serviceName), NamingUtils.getServiceName(serviceName),
                instance.getIp(), instance.getPort()));
        return "ok";
    }
    

跟进getInstanceOperator().registerInstance(namespaceId, serviceName, instance);

InstanceOperatorServiceImpl#registerInstance

    @Override
    public void registerInstance(String namespaceId, String serviceName, Instance instance) throws NacosException {
    
        com.alibaba.nacos.naming.core.Instance coreInstance = parseInstance(instance);
        // 跟进
        serviceManager.registerInstance(namespaceId, serviceName, coreInstance);
    }

跟进serviceManager.registerInstance(namespaceId, serviceName, coreInstance);

ServiceManager#registerInstance

    public void registerInstance(String namespaceId, String serviceName, Instance instance) throws NacosException {
    
        
        NamingUtils.checkInstanceIsLegal(instance);
        // 跟进
        createEmptyService(namespaceId, serviceName, instance.isEphemeral());
        
        Service service = getService(namespaceId, serviceName);
        
        checkServiceIsNull(service, namespaceId, serviceName);
        
        addInstance(namespaceId, serviceName, instance.isEphemeral(), instance);
    }
    

跟进createEmptyService(namespaceId, serviceName, instance.isEphemeral());

最后我们来到ServiceManager#createServiceIfAbsent

 public void createServiceIfAbsent(String namespaceId, String serviceName, boolean local, Cluster cluster)
            throws NacosException {
    
        Service service = getService(namespaceId, serviceName);
        //return if service already exists
        if (service != null) {
    
            return;
        }

        Loggers.SRV_LOG.info("creating empty service {}:{}", namespaceId, serviceName);
        service = new Service();
        service.setName(serviceName);
        service.setNamespaceId(namespaceId);
        service.setGroupName(NamingUtils.getGroupName(serviceName));
        // now validate the service. if failed, exception will be thrown
        service.setLastModifiedMillis(System.currentTimeMillis());
        service.recalculateChecksum();
        if (cluster != null) {
    
            cluster.setService(service);
            service.getClusterMap().put(cluster.getName(), cluster);
        }
        service.validate();
		
		// 跟进
        putServiceAndInit(service);
        if (!local) {
    
            addOrReplaceService(service);
        }
    }

跟进putServiceAndInit(service);

private void putServiceAndInit(Service service) throws NacosException {
    
		// 跟进
        putService(service);
        service = getService(service.getNamespaceId(), service.getName());
        service.init();
        consistencyService
                .listen(KeyBuilder.buildInstanceListKey(service.getNamespaceId(), service.getName(), true), service);
        consistencyService
                .listen(KeyBuilder.buildInstanceListKey(service.getNamespaceId(), service.getName(), false), service);
        Loggers.SRV_LOG.info("[NEW-SERVICE] {}", service.toJson());
    }

跟进putService(service);

    public void putService(Service service) {
    
        if (!serviceMap.containsKey(service.getNamespaceId())) {
    
       		// Store client information in server memory
            serviceMap.putIfAbsent(service.getNamespaceId(), new ConcurrentSkipListMap<>());
        }
        serviceMap.get(service.getNamespaceId()).putIfAbsent(service.getName(), service);
    }
    

再看一眼这个serviceMap的定义

/** * Map(namespace, Map(group::serviceName, Service)). */
private final Map<String, Map<String, Service>> serviceMap = new ConcurrentHashMap<>();

来吧,总结一下吧,It is roughly divided into these steps：

1. 在Spring启动时,先发布Nacos服务注册的事件
2. 实例化NacosCore class for service registrationNacosAutoServiceRegistration,并监听事件
3. 监听到事件之后,对事件进行处理,封装Nacos客户端信息,并发送API请求到Nacos服务端接口
4. 服务端接收到请求之后,save data to initializedConcurrentHashMap中,One-time service registration

接下来,Let's analyze it step by stepNacosThe other core mechanism,and handwritten a registry,Let everyone better understand these distributed middleware.