Eureka Client源码解析回顾

一 概述

Eureka Client通过Starter的方式引入依赖，Spring Boot将会为项目使不同的注解进行自动配置。

• EurekaClientAutoConfiguration：Eureka Client自动配置类，负责Eureka Client中关键Beans的配置和初始化，如ApplicationInfoManager和EurekaClientConfig等。
• RibbonEurekaAutoConfiguration：Ribbon负载均衡相关配置。
• EurekaDiscoveryClientConfiguratino：配置自动注册和应用的健康检查器。

二 Eureka Client的完整工作流程

应用启动阶段

1. 读取与Eureka Server交互的配置信息，封装成EurekaClientConfig。
2. 读取自身服务实例配置信息，封装成EurekaInstanceConfig。
3. 从Eureka Server中拉取注册表信息并缓存到本地。
4. 服务注册。
5. 初始化发送心跳，缓存刷新(拉取注册表信息更新本地缓存)和按需注册(监控服务实例信息变化，决定是否重新发起注册，更新注册表中的服务实例元数据）定时任务。

应用执行阶段

1. 定时发送心跳到Eureka Server中，维持在注册表的租约。
2. 定时从Eureka Server中拉取注册表信息，更新本地注册表缓存。
3. 监控一个用自身信息变化，若发生变化，需要重新发起服务注册。

应用销毁阶段

1. 从Eureka Server注销自身服务实例。

三 配置类EurekaDiscoveryClientConfiguration

源码

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@ConditionalOnDiscoveryEnabled
@ConditionalOnBlockingDiscoveryEnabled
public class EurekaDiscoveryClientConfiguration {

	@Bean
	@ConditionalOnMissingBean
	public EurekaDiscoveryClient discoveryClient(EurekaClient client, EurekaClientConfig clientConfig) {
		return new EurekaDiscoveryClient(client, clientConfig);
	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnProperty(value = "eureka.client.healthcheck.enabled", matchIfMissing = false)
	protected static class EurekaHealthCheckHandlerConfiguration {

		@Autowired(required = false)
		private StatusAggregator statusAggregator = new SimpleStatusAggregator();

		@Bean
		@ConditionalOnMissingBean(HealthCheckHandler.class)
		public EurekaHealthCheckHandler eurekaHealthCheckHandler() {
			return new EurekaHealthCheckHandler(this.statusAggregator);
		}
	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(RefreshScopeRefreshedEvent.class)
	protected static class EurekaClientConfigurationRefresher
			implements ApplicationListener<RefreshScopeRefreshedEvent> {

		@Autowired(required = false)
		private EurekaClient eurekaClient;

		@Autowired(required = false)
		private EurekaAutoServiceRegistration autoRegistration;

		public void onApplicationEvent(RefreshScopeRefreshedEvent event) {
			// This will force the creation of the EurkaClient bean if not already created
			// to make sure the client will be reregistered after a refresh event
			if (eurekaClient != null) {
				eurekaClient.getApplications();
			}
			if (autoRegistration != null) {
				// register in case meta data changed
				this.autoRegistration.stop();
				this.autoRegistration.start();
			}
		}
	}
}

EurekaDiscoveryClientConfiguration中属性读取和配置类

类名	作用和介绍
EurekaClientConfig	封装Eureka Client与Eureka Server交互所需要的配置信息。Spring Cloud为其提供了一个默认配置Eureka的配置类EurekaClientConfigBean，可以在配置文件中通过前缀eureka.client + 属性名进行属性覆盖。
ApplicationInfoManager	作为应用信息管理，管理服务实例的信息类InstanceInfo和服务实例的配置信息类EurekaInstanceConfig。
InstanceInfo	封装将被发送到Eureka Server进行服务注册和服务实例元数据。它在Eureka Server的注册表中代表一个服务实例，其他服务实例可以通过InstanceInfo了解该服务实例的相关信息从而发起服务请求。
EurekaInstanceConfig	封装Eureka Client自身服务实例的配置信息，主要用于构建InstanceInfo，通常这些信息在配置文件中的eureka.instance前缀下进行设置，Spring Cloud通过EurekaInstanceConfigBean配置类提供了默认配置。
DiscoveryClient	Spring Cloud中定义用来服务发现的客户端接口。

默认配置类EurekaClientConfigBean的部分信息源码

@ConfigurationProperties(EurekaClientConfigBean.PREFIX)
public class EurekaClientConfigBean implements EurekaClientConfig, Ordered {

	public static final String PREFIX = "eureka.client";

	public static final String DEFAULT_URL = "http://localhost:8761" + DEFAULT_PREFIX + "/";

	public static final String DEFAULT_ZONE = "defaultZone";

	private static final int MINUTES = 60;

	@Autowired(required = false)
	PropertyResolver propertyResolver;

	private boolean enabled = true;

	@NestedConfigurationProperty
	private EurekaTransportConfig transport = new CloudEurekaTransportConfig();

	private int registryFetchIntervalSeconds = 30;

	private int instanceInfoReplicationIntervalSeconds = 30;

	private int initialInstanceInfoReplicationIntervalSeconds = 40;

	private int eurekaServiceUrlPollIntervalSeconds = 5 * MINUTES;

	private String proxyPort;

	private String proxyHost;

	private String proxyUserName;

	private String proxyPassword;

	private int eurekaServerReadTimeoutSeconds = 8;

	private int eurekaServerConnectTimeoutSeconds = 5;

	private String backupRegistryImpl;

	private int eurekaServerTotalConnections = 200;

	private int eurekaServerTotalConnectionsPerHost = 50;

	private String eurekaServerURLContext;

	private String eurekaServerPort;

	private String eurekaServerDNSName;

	private String region = "us-east-1";

	private int eurekaConnectionIdleTimeoutSeconds = 30;

	private String registryRefreshSingleVipAddress;

	private int heartbeatExecutorThreadPoolSize = 2;

	private int heartbeatExecutorExponentialBackOffBound = 10;

	private int cacheRefreshExecutorThreadPoolSize = 2;

	private int cacheRefreshExecutorExponentialBackOffBound = 10;

	private Map<String, String> serviceUrl = new HashMap<>();

	{
		this.serviceUrl.put(DEFAULT_ZONE, DEFAULT_URL);
	}

	private boolean gZipContent = true;

	private boolean useDnsForFetchingServiceUrls = false;

	private boolean registerWithEureka = true;

	private boolean preferSameZoneEureka = true;

	private boolean logDeltaDiff;

	private boolean disableDelta;

	private String fetchRemoteRegionsRegistry;

	private Map<String, String> availabilityZones = new HashMap<>();

	private boolean filterOnlyUpInstances = true;

	private boolean fetchRegistry = true;

	private String dollarReplacement = "_-";

	private String escapeCharReplacement = "__";

	private boolean allowRedirects = false;

	private boolean onDemandUpdateStatusChange = true;

	private String encoderName;

	private String decoderName;

	private String clientDataAccept = EurekaAccept.full.name();

	private boolean shouldUnregisterOnShutdown = true;

	private boolean shouldEnforceRegistrationAtInit = false;

	private int order = 0;
}

继续复习总结中，待续！