聊聊EurekaHealthCheckHandler

序

本文主要研究一下EurekaHealthCheckHandler

HealthCheckHandler

eureka-client-1.8.8-sources.jar!/com/netflix/appinfo/HealthCheckHandler.java

/**
 * This provides a more granular healthcheck contract than the existing {@link HealthCheckCallback}
 *
 * @author Nitesh Kant
 */
public interface HealthCheckHandler {

    InstanceInfo.InstanceStatus getStatus(InstanceInfo.InstanceStatus currentStatus);

}

netflix的eureka-client提供了HealthCheckHandler接口，用來對獲取服務實例的健康狀態

HealthCheckCallbackToHandlerBridge

eureka-client-1.8.8-sources.jar!/com/netflix/appinfo/HealthCheckCallbackToHandlerBridge.java

@SuppressWarnings("deprecation")
public class HealthCheckCallbackToHandlerBridge implements HealthCheckHandler {

    private final HealthCheckCallback callback;

    public HealthCheckCallbackToHandlerBridge() {
        callback = null;
    }

    public HealthCheckCallbackToHandlerBridge(HealthCheckCallback callback) {
        this.callback = callback;
    }

    @Override
    public InstanceInfo.InstanceStatus getStatus(InstanceInfo.InstanceStatus currentStatus) {
        if (null == callback || InstanceInfo.InstanceStatus.STARTING == currentStatus
                || InstanceInfo.InstanceStatus.OUT_OF_SERVICE == currentStatus) { // Do not go to healthcheck handler if the status is starting or OOS.
            return currentStatus;
        }

        return callback.isHealthy() ? InstanceInfo.InstanceStatus.UP : InstanceInfo.InstanceStatus.DOWN;
    }
}

這個類被標記爲廢棄，若是沒有callback，或者當前狀態是STARTING或OUT_OF_SERVICE，都會返回當前狀態；不然纔會調用callback的isHealthy方法來判斷是UP仍是DOWN.也就是說若是沒有callback，一開始啓動的時候是UP，則以後都是返回UP

registerHealthCheck

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/DiscoveryClient.java

/**
     * Register {@link HealthCheckCallback} with the eureka client.
     *
     * Once registered, the eureka client will invoke the
     * {@link HealthCheckCallback} in intervals specified by
     * {@link EurekaClientConfig#getInstanceInfoReplicationIntervalSeconds()}.
     *
     * @param callback app specific healthcheck.
     *
     * @deprecated Use
     */
    @Deprecated
    @Override
    public void registerHealthCheckCallback(HealthCheckCallback callback) {
        if (instanceInfo == null) {
            logger.error("Cannot register a listener for instance info since it is null!");
        }
        if (callback != null) {
            healthCheckHandler = new HealthCheckCallbackToHandlerBridge(callback);
        }
    }

    @Override
    public void registerHealthCheck(HealthCheckHandler healthCheckHandler) {
        if (instanceInfo == null) {
            logger.error("Cannot register a healthcheck handler when instance info is null!");
        }
        if (healthCheckHandler != null) {
            this.healthCheckHandler = healthCheckHandler;
            // schedule an onDemand update of the instanceInfo when a new healthcheck handler is registered
            if (instanceInfoReplicator != null) {
                instanceInfoReplicator.onDemandUpdate();
            }
        }
    }

registerHealthCheckCallback被標記爲廢棄，緣由是它默認註冊了一個HealthCheckCallbackToHandlerBridge；後續是在這個方法裏頭處理fallback邏輯

getHealthCheckHandler

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/DiscoveryClient.java

@Override
    public HealthCheckHandler getHealthCheckHandler() {
        if (healthCheckHandler == null) {
            if (null != healthCheckHandlerProvider) {
                healthCheckHandler = healthCheckHandlerProvider.get();
            } else if (null != healthCheckCallbackProvider) {
                healthCheckHandler = new HealthCheckCallbackToHandlerBridge(healthCheckCallbackProvider.get());
            }

            if (null == healthCheckHandler) {
                healthCheckHandler = new HealthCheckCallbackToHandlerBridge(null);
            }
        }

        return healthCheckHandler;
    }

這裏判斷，若是最後healthCheckHandler爲null，則會建立HealthCheckCallbackToHandlerBridge

HealthCheckCallback

eureka-client-1.8.8-sources.jar!/com/netflix/appinfo/HealthCheckCallback.java

@Deprecated
public interface HealthCheckCallback {
    /**
     * If false, the instance will be marked
     * {@link InstanceInfo.InstanceStatus#DOWN} with eureka. If the instance was
     * already marked {@link InstanceInfo.InstanceStatus#DOWN} , returning true
     * here will mark the instance back to
     * {@link InstanceInfo.InstanceStatus#UP}.
     *
     * @return true if the call back returns healthy, false otherwise.
     */
    boolean isHealthy();
}

HealthCheckCallback目前被標記爲廢棄，能夠理解爲最後的healthCheckHandler = new HealthCheckCallbackToHandlerBridge(null);

EurekaServiceRegistry

spring-cloud-netflix-eureka-client-2.0.0.RC1-sources.jar!/org/springframework/cloud/netflix/eureka/serviceregistry/EurekaServiceRegistry.java

@Override
    public void register(EurekaRegistration reg) {
        maybeInitializeClient(reg);

        if (log.isInfoEnabled()) {
            log.info("Registering application " + reg.getInstanceConfig().getAppname()
                    + " with eureka with status "
                    + reg.getInstanceConfig().getInitialStatus());
        }

        reg.getApplicationInfoManager()
                .setInstanceStatus(reg.getInstanceConfig().getInitialStatus());

        reg.getHealthCheckHandler().ifAvailable(healthCheckHandler ->
                reg.getEurekaClient().registerHealthCheck(healthCheckHandler));
    }

這個方法判斷，若是有healthCheckHandler實例，則纔會調用registerHealthCheck去註冊。

EurekaDiscoveryClientConfiguration

spring-cloud-netflix-eureka-client-2.0.0.RC1-sources.jar!/org/springframework/cloud/netflix/eureka/EurekaDiscoveryClientConfiguration.java

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

    class Marker {}

    @Bean
    public Marker eurekaDiscoverClientMarker() {
        return new Marker();
    }

    @Configuration
    @ConditionalOnClass(RefreshScopeRefreshedEvent.class)
    protected static class EurekaClientConfigurationRefresher {

        @Autowired(required = false)
        private EurekaClient eurekaClient;

        @Autowired(required = false)
        private EurekaAutoServiceRegistration autoRegistration;

        @EventListener(RefreshScopeRefreshedEvent.class)
        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();
            }
        }
    }


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

        @Autowired(required = false)
        private HealthAggregator healthAggregator = new OrderedHealthAggregator();

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

默認eureka.client.healthcheck.enabled爲false，若是設置爲true的話則會注入EurekaHealthCheckHandler

EurekaHealthCheckHandler

spring-cloud-netflix-eureka-client-2.0.0.RC1-sources.jar!/org/springframework/cloud/netflix/eureka/EurekaHealthCheckHandler.java

public class EurekaHealthCheckHandler implements HealthCheckHandler, ApplicationContextAware, InitializingBean {

    private static final Map<Status, InstanceInfo.InstanceStatus> STATUS_MAPPING =
            new HashMap<Status, InstanceInfo.InstanceStatus>() {{
                put(Status.UNKNOWN, InstanceStatus.UNKNOWN);
                put(Status.OUT_OF_SERVICE, InstanceStatus.OUT_OF_SERVICE);
                put(Status.DOWN, InstanceStatus.DOWN);
                put(Status.UP, InstanceStatus.UP);
            }};

    private final CompositeHealthIndicator healthIndicator;

    private ApplicationContext applicationContext;

    public EurekaHealthCheckHandler(HealthAggregator healthAggregator) {
        Assert.notNull(healthAggregator, "HealthAggregator must not be null");
        this.healthIndicator = new CompositeHealthIndicator(healthAggregator);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        final Map<String, HealthIndicator> healthIndicators = applicationContext.getBeansOfType(HealthIndicator.class);

        for (Map.Entry<String, HealthIndicator> entry : healthIndicators.entrySet()) {

            //ignore EurekaHealthIndicator and flatten the rest of the composite
            //otherwise there is a never ending cycle of down. See gh-643
            if (entry.getValue() instanceof DiscoveryCompositeHealthIndicator) {
                DiscoveryCompositeHealthIndicator indicator = (DiscoveryCompositeHealthIndicator) entry.getValue();
                for (DiscoveryCompositeHealthIndicator.Holder holder : indicator.getHealthIndicators()) {
                    if (!(holder.getDelegate() instanceof EurekaHealthIndicator)) {
                        healthIndicator.addHealthIndicator(holder.getDelegate().getName(), holder);
                    }
                }

            }
            else {
                healthIndicator.addHealthIndicator(entry.getKey(), entry.getValue());
            }
        }
    }

    @Override
    public InstanceStatus getStatus(InstanceStatus instanceStatus) {
        return getHealthStatus();
    }

    protected InstanceStatus getHealthStatus() {
        final Status status = getHealthIndicator().health().getStatus();
        return mapToInstanceStatus(status);
    }

    protected InstanceStatus mapToInstanceStatus(Status status) {
        if (!STATUS_MAPPING.containsKey(status)) {
            return InstanceStatus.UNKNOWN;
        }
        return STATUS_MAPPING.get(status);
    }

    protected CompositeHealthIndicator getHealthIndicator() {
        return healthIndicator;
    }
}

能夠看到在afterPropertiesSet的時候，將整個springboot的healthIndicator添加進來並轉化映射爲eureka的InstanceStatus，組合爲CompositeHealthIndicator。而client的health check則會調用這個getStatus接口，返回的是compositeHealthIndicator的健康狀態。

小結

eureka client的health check默認是false，即最後使用的是HealthCheckCallbackToHandlerBridge，即HealthCheckCallbackToHandlerBridge(null)，callback爲null，則默認返回的都是啓動時註冊的狀態，通常是UP。若是開啓eureka.client.healthcheck.enabled=true則會將springboot的actuator的health indicator都歸入health check當中。

doc

• multi__service_discovery_eureka_clients.html#_eureka_s_health_checks