深入理解DiscoveryClient

Spring Cloud Commons 提供的抽象

　　最早的时候服务发现注册都是通过DiscoveryClient来实现的，随着版本变迁把DiscoveryClient服务注册抽离出来变成了ServiceRegistry抽象，专门负责服务注册，DiscoveryClient专门负责服务发现。还提供了负载均衡的发现LoadBalancerClient抽象。

DiscoveryClient通过@EnableDiscoveryClient的方式进行启用。

自动向Eureka服务端注册

　　ServiceRegistry使用的式EurekaServiceRegistry 来做的注册， 注册信息放在EurekaRegistration中

　　源码：

public interface ServiceRegistry<R extends Registration> {

    /**注册
        */

    void register(R registration);

    /**
     * 取消注册
     *
     */
    void deregister(R registration);

    /**
     * 关闭服务
     */
    void close();

    /**
     *设置状态
     */
    void setStatus(R registration, String status);

    /**
     * 获取状态
     */
    <T> T getStatus(R registration);

}                

EurekaServiceRegistry的实现

import java.util.HashMap;

import com.netflix.appinfo.InstanceInfo;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.cloud.client.serviceregistry.ServiceRegistry;

import static com.netflix.appinfo.InstanceInfo.InstanceStatus.UNKNOWN;

/**
 * @author Spencer Gibb
 */
public class EurekaServiceRegistry implements ServiceRegistry<EurekaRegistration> {

    private static final Log log = LogFactory.getLog(EurekaServiceRegistry.class);
　　
　　　　// 获取到EurekaRegistration 信息

@Override public void register(EurekaRegistration reg) {
　　　　　// 初始化信息
        maybeInitializeClient(reg);

        if (log.isInfoEnabled()) {
            log.info("Registering application "
                    + reg.getApplicationInfoManager().getInfo().getAppName()
                    + " with eureka with status "
                    + reg.getInstanceConfig().getInitialStatus());
        }
　　　　　　// 设置实例状态
        reg.getApplicationInfoManager()
                .setInstanceStatus(reg.getInstanceConfig().getInitialStatus());
　　　　　　// 如果有healthCheckHandler 设置 healthCheck
        reg.getHealthCheckHandler().ifAvailable(healthCheckHandler -> reg
                .getEurekaClient().registerHealthCheck(healthCheckHandler));
    }

    private void maybeInitializeClient(EurekaRegistration reg) {
        // force initialization of possibly scoped proxies
        reg.getApplicationInfoManager().getInfo();
        reg.getEurekaClient().getApplications();
    }

    @Override
    public void deregister(EurekaRegistration reg) {
        if (reg.getApplicationInfoManager().getInfo() != null) {

            if (log.isInfoEnabled()) {
                log.info("Unregistering application "
                        + reg.getApplicationInfoManager().getInfo().getAppName()
                        + " with eureka with status DOWN");
            }
　　　　　　　　//将状态设置为DOWN
            reg.getApplicationInfoManager()
                    .setInstanceStatus(InstanceInfo.InstanceStatus.DOWN);

            // shutdown of eureka client should happen with EurekaRegistration.close()
            // auto registration will create a bean which will be properly disposed
            // manual registrations will need to call close()
        }
    }

    @Override
    public void setStatus(EurekaRegistration registration, String status) {
        InstanceInfo info = registration.getApplicationInfoManager().getInfo();

        // TODO: howto deal with delete properly?
        if ("CANCEL_OVERRIDE".equalsIgnoreCase(status)) {
            registration.getEurekaClient().cancelOverrideStatus(info);
            return;
        }

        // TODO: howto deal with status types across discovery systems?
        InstanceInfo.InstanceStatus newStatus = InstanceInfo.InstanceStatus
                .toEnum(status);
        registration.getEurekaClient().setStatus(newStatus, info);
    }

    @Override
    public Object getStatus(EurekaRegistration registration) {
        String appname = registration.getApplicationInfoManager().getInfo().getAppName();
        String instanceId = registration.getApplicationInfoManager().getInfo().getId();
        InstanceInfo info = registration.getEurekaClient().getInstanceInfo(appname,
                instanceId);

        HashMap<String, Object> status = new HashMap<>();
        if (info != null) {
            status.put("status", info.getStatus().toString());
            status.put("overriddenStatus", info.getOverriddenStatus().toString());
        }
        else {
            status.put("status", UNKNOWN.toString());
        }

        return status;
    }

    public void close() {
    }

}

DefaultLifecycleProcessor中start的调用

public void start() {
        startBeans(false);
        this.running = true;
    }

private void startBeans(boolean autoStartupOnly) {
　　　　// 找到所有声明周期中的bean
        Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
        Map<Integer, LifecycleGroup> phases = new HashMap<>();
        lifecycleBeans.forEach((beanName, bean) -> {
            if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
                int phase = getPhase(bean);
                LifecycleGroup group = phases.get(phase);
                if (group == null) {
                    group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
                    phases.put(phase, group);
                }
                group.add(beanName, bean);
            }
        });
        if (!phases.isEmpty()) {
            List<Integer> keys = new ArrayList<>(phases.keySet());
            Collections.sort(keys);
            for (Integer key : keys) {
　　　　　　　　　　// 只要不为空，每一个调用start方法
                phases.get(key).start();
            }
        }
    }

public void start() {
   if (this.members.isEmpty()) {
      return;
   }
   if (logger.isDebugEnabled()) {
      logger.debug("Starting beans in phase " + this.phase);
   }
   Collections.sort(this.members);
   for (LifecycleGroupMember member : this.members) {
      doStart(this.lifecycleBeans, member.name, this.autoStartupOnly);
   }
}

private void doStart(Map<String, ? extends Lifecycle> lifecycleBeans, String beanName, boolean autoStartupOnly) {
        Lifecycle bean = lifecycleBeans.remove(beanName);
        if (bean != null && bean != this) {
            String[] dependenciesForBean = getBeanFactory().getDependenciesForBean(beanName);
            for (String dependency : dependenciesForBean) {
                doStart(lifecycleBeans, dependency, autoStartupOnly);
            }
            if (!bean.isRunning() &&
                    (!autoStartupOnly || !(bean instanceof SmartLifecycle) || ((SmartLifecycle) bean).isAutoStartup())) {
                if (logger.isTraceEnabled()) {
                    logger.trace("Starting bean '" + beanName + "' of type [" + bean.getClass().getName() + "]");
                }
                try {
                    bean.start();
                }
                catch (Throwable ex) {
                    throw new ApplicationContextException("Failed to start bean '" + beanName + "'", ex);
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Successfully started bean '" + beanName + "'");
                }
            }
        }
    }

DiscoveryClient

public interface DiscoveryClient extends Ordered {

    /**
     * Default order of the discovery client.
     */
    int DEFAULT_ORDER = 0;

    /**
     * A human-readable description of the implementation, used in HealthIndicator. 提供一些描述信息
     * @return The description.
     */
    String description();

    /**
     * Gets all ServiceInstances associated with a particular serviceId.
     * @param serviceId The serviceId to query.
     * @return A List of ServiceInstance. 根据serviceid 找到ServiceInstance
     */
    List<ServiceInstance> getInstances(String serviceId);

    /**
     * @return All known service IDs. 获取所有的服务
     */
    List<String> getServices();

    /**
     * Default implementation for getting order of discovery clients.
     * @return order
     */
    @Override
    default int getOrder() {
        return DEFAULT_ORDER;
    }

}

Eureka的实现

import java.net.URI;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import com.netflix.appinfo.EurekaInstanceConfig;
import com.netflix.appinfo.InstanceInfo;
import com.netflix.discovery.EurekaClient;
import com.netflix.discovery.EurekaClientConfig;
import com.netflix.discovery.shared.Application;
import com.netflix.discovery.shared.Applications;

import org.springframework.cloud.client.DefaultServiceInstance;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.core.Ordered;
import org.springframework.util.Assert;

import static com.netflix.appinfo.InstanceInfo.PortType.SECURE;

/**
 * A {@link DiscoveryClient} implementation for Eureka.
 *
 * @author Spencer Gibb
 * @author Tim Ysewyn
 */
public class EurekaDiscoveryClient implements DiscoveryClient {

    /**
     * Client description {@link String}.
     */
    public static final String DESCRIPTION = "Spring Cloud Eureka Discovery Client";

    private final EurekaClient eurekaClient;

    private final EurekaClientConfig clientConfig;

    @Deprecated
    public EurekaDiscoveryClient(EurekaInstanceConfig config, EurekaClient eurekaClient) {
        this(eurekaClient, eurekaClient.getEurekaClientConfig());
    }

    public EurekaDiscoveryClient(EurekaClient eurekaClient,
            EurekaClientConfig clientConfig) {
        this.clientConfig = clientConfig;
        this.eurekaClient = eurekaClient;
    }

    @Override
    public String description() {
        return DESCRIPTION;
    }
　　　　// 通过serviceid 获取到 instanceInfo信息
    @Override
    public List<ServiceInstance> getInstances(String serviceId) {
        List<InstanceInfo> infos = this.eurekaClient.getInstancesByVipAddress(serviceId,
                false);
        List<ServiceInstance> instances = new ArrayList<>();
        for (InstanceInfo info : infos) {
            instances.add(new EurekaServiceInstance(info));
        }
        return instances;
    }

    @Override
    public List<String> getServices() {
        Applications applications = this.eurekaClient.getApplications();
        if (applications == null) {
            return Collections.emptyList();
        }
        List<Application> registered = applications.getRegisteredApplications();
        List<String> names = new ArrayList<>();
        for (Application app : registered) {
            if (app.getInstances().isEmpty()) {
                continue;
            }
            names.add(app.getName().toLowerCase());

        }
        return names;
    }

    @Override
    public int getOrder() {
        return clientConfig instanceof Ordered ? ((Ordered) clientConfig).getOrder()
                : DiscoveryClient.DEFAULT_ORDER;
    }

    /**
     * An Eureka-specific {@link ServiceInstance} implementation.
     */
    public static class EurekaServiceInstance implements ServiceInstance {

        private InstanceInfo instance;

        public EurekaServiceInstance(InstanceInfo instance) {
            Assert.notNull(instance, "Service instance required");
            this.instance = instance;
        }

        public InstanceInfo getInstanceInfo() {
            return instance;
        }

        @Override
        public String getInstanceId() {
            return this.instance.getId();
        }

        @Override
        public String getServiceId() {
            return this.instance.getAppName();
        }

        @Override
        public String getHost() {
            return this.instance.getHostName();
        }

        @Override
        public int getPort() {
            if (isSecure()) {
                return this.instance.getSecurePort();
            }
            return this.instance.getPort();
        }

        @Override
        public boolean isSecure() {
            // assume if secure is enabled, that is the default
            return this.instance.isPortEnabled(SECURE);
        }

        @Override
        public URI getUri() {
            return DefaultServiceInstance.getUri(this);
        }

        @Override
        public Map<String, String> getMetadata() {
            return this.instance.getMetadata();
        }

    }

}

总结:

自动配置注册:

EurekaAutoServiceRegistration::start(在DefaultLifecycleProcessor中调用):

1. 先检查port;
2. 如果没有启动过并且非安全的端口大于0,则进行注册(通过调用org.springframework.cloud.client.serviceregistry.ServiceRegistry接口的实例).
3. 注册事件;
4. 设置运行状态
注册:
org.springframework.cloud.client.serviceregistry.ServiceRegistry->注册和取消注册
->
EurekaServiceRegistry::register从参数获取EurekaRegistration,
并初始化EurekaRegistration,通过ApplicationInfoManager设置实例的状态,
如果有healthCheck则注册healthCheck.
自动配置取消注册:

1. 调用org.springframework.cloud.client.serviceregistry.ServiceRegistry接口的实例的deregister方法.
2. 设置状态

取消注册(EurekaServiceRegistry::deregister):

将状态设置成DOWN.

ServiceInstance