來源：SegmentFault 思否社區(qū)

作者：無名?

基于

spring-cloud-Greenwich.RELEASE
spring-boot-2.1.3.RELEASE
spring-boot-starter-actuator-2.1.3.RELEASE
Spring-cloud-netflix-eureka-client-2.1.0.RELEASE

背景

線上請求項目接口，spring-cloud-gateway返回404，排查發(fā)現(xiàn)是gateway無法從eureka-server獲取到項目有效的注冊信息。同時當(dāng)時由于網(wǎng)絡(luò)問題，項目無法連上數(shù)據(jù)庫。但是這次出現(xiàn)的網(wǎng)絡(luò)問題，可能影響到項目與數(shù)據(jù)庫的連接，并不影響項目與eureka-server的連接。

通過日志，看到項目一直在對數(shù)據(jù)庫做健康檢測，并且因為無法連上而一直有異常日志，同時看到了Eureka下線通知的日志Saw local status change event DOWN，而這兩個日志都是在同一個線程里打印的，線程串聯(lián)DiscoveryClient-InstanceInfoReplicator-0，既然是同一個線程，那說明是兩者之間必然有關(guān)聯(lián)。

那是什么原因?qū)е耬ureka-server沒有項目的注冊信息？這個要從Eureka-Client的健康檢測說起。

健康監(jiān)測

按照常規(guī)，要了解原理，就從閱讀二進(jìn)制入手。

Eureke-client的初始化基本上都是在DiscoveryClient類內(nèi)完成的，包括啟動健康監(jiān)測定時任務(wù)。

public class DiscoveryClient implements EurekaClient {private void initScheduledTasks() {        ……if (clientConfig.shouldRegisterWithEureka()) {            ……// InstanceInfo replicator            instanceInfoReplicator = new InstanceInfoReplicator(this,                    instanceInfo,                    clientConfig.getInstanceInfoReplicationIntervalSeconds(),2); // burstSize            ……            instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());        } else {            logger.info("Not registering with Eureka server per configuration");        }    }}

在InstanceInfoReplicator內(nèi)接通本節(jié)能檢查系統(tǒng)健康并刷新當(dāng)前Eureka-client節(jié)點狀態(tài)。

class InstanceInfoReplicator implements Runnable {public void run() {try {            discoveryClient.refreshInstanceInfo();            ……        } catch (Throwable t) {            logger.warn("There was a problem with the instance info replicator", t);        } finally {            Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);            scheduledPeriodicRef.set(next);        }    }}
public class DiscoveryClient implements EurekaClient {void refreshInstanceInfo() {        ……        InstanceStatus status;try {            status = getHealthCheckHandler().getStatus(instanceInfo.getStatus());        } catch (Exception e) {            logger.warn("Exception from healthcheckHandler.getStatus, setting status to DOWN", e);            status = InstanceStatus.DOWN;        }if (null != status) {            applicationInfoManager.setInstanceStatus(status);        }    }}

這里通過HealthCheckHandler獲取instanceInfo的status并修改節(jié)點狀態(tài)和下發(fā)事件通知，如果獲取到的status是DOWN，那這時候事件監(jiān)聽器就打印了我們在開頭看到的日志，并且上報給Eureka-server的中斷狀態(tài)也是DOWN，最終導(dǎo)致此問題的出現(xiàn)：網(wǎng)關(guān)無法從Eureka-server獲取到狀態(tài)為UP的路由器。

public class ApplicationInfoManager {public synchronized void setInstanceStatus(InstanceStatus status) {        InstanceStatus next = instanceStatusMapper.map(status);if (next == null) {return;        }        InstanceStatus prev = instanceInfo.setStatus(next);if (prev != null) {for (StatusChangeListener listener : listeners.values()) {try {                    listener.notify(new StatusChangeEvent(prev, next));                } catch (Exception e) {                    logger.warn("failed to notify listener: {}", listener.getId(), e);                }            }        }    }}
public class DiscoveryClient implements EurekaClient {private void initScheduledTasks() {        ……if (clientConfig.shouldRegisterWithEureka()) {            ……            statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {@Overridepublic String getId() {return "statusChangeListener";                }@Overridepublic void notify(StatusChangeEvent statusChangeEvent) {if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||                            InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {// log at warn level if DOWN was involved                        logger.warn("Saw local status change event {}", statusChangeEvent);                    } else {                        logger.info("Saw local status change event {}", statusChangeEvent);                    }                    instanceInfoReplicator.onDemandUpdate();                }            };        } else {            logger.info("Not registering with Eureka server per configuration");        }    }}

這里的重點就是DiscoveryClient的

getHealthCheckHandler().getStatus(instanceInfo.getStatus())是怎么獲取到值的？

getHealthCheckHandler返回的是EurekaHealthCheckHandler，繼續(xù)跟進(jìn)原始碼進(jìn)入到EurekaHealthCheckHandler類。

public class EurekaHealthCheckHandler implements HealthCheckHandler, ApplicationContextAware, InitializingBean {private final CompositeHealthIndicator healthIndicator;@Overridepublic void afterPropertiesSet() throws Exception {final Map healthIndicators = applicationContext.getBeansOfType(HealthIndicator.class);for (Map.Entry entry : healthIndicators.entrySet()) {//ignore EurekaHealthIndicator and flatten the rest of the composite//otherwise there is a never ending cycle of down. See gh-643if (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());            }        }    }}

在afterPropertiesSet方法內(nèi)部通過applicationContext.getBeansOfType獲取到所有的健康檢測類HealthIndicator。

注：applicationContext.getBeansOfType方法是通過遍歷BeanDefinition獲取所有beanName，然后遍歷beanName，確定如果當(dāng)前beanName未創(chuàng)建實例替換創(chuàng)建了對應(yīng)的Bean對象實例。則會applicationContext.getBeansOfType確保將指定類型的所有的Bean對象都創(chuàng)造好。

public class EurekaHealthCheckHandler implements HealthCheckHandler, ApplicationContextAware, InitializingBean {public InstanceStatus getStatus(InstanceStatus instanceStatus) {return getHealthStatus();    }
protected InstanceStatus getHealthStatus() {final Status status = getHealthIndicator().health().getStatus();return mapToInstanceStatus(status);    }
protected CompositeHealthIndicator getHealthIndicator() {return healthIndicator;    }}

調(diào)用CompositeHealthIndicator的health方法獲取狀態(tài)，從前面的afterPropertiesSet方法可以看到，CompositeHealthIndicator是一個HealthIndicator合集。

public class CompositeHealthIndicator implements HealthIndicator {public void addHealthIndicator(String name, HealthIndicator indicator) {this.registry.register(name, indicator);    }@Overridepublic Health health() {        Map healths = new LinkedHashMap<>();for (Map.Entry entry : this.registry.getAll()                .entrySet()) {            healths.put(entry.getKey(), entry.getValue().health());        }return this.aggregator.aggregate(healths);    }}
public class OrderedHealthAggregator extends AbstractHealthAggregator {public OrderedHealthAggregator() {        setStatusOrder(Status.DOWN, Status.OUT_OF_SERVICE, Status.UP, Status.UNKNOWN);    }
public void setStatusOrder(Status... statusOrder) {        String[] order = new String[statusOrder.length];for (int i = 0; i < statusOrder.length; i++) {            order[i] = statusOrder[i].getCode();        }        setStatusOrder(Arrays.asList(order));    }
@Overridepublic final Health aggregate(Map healths) {        List statusCandidates = healths.values().stream().map(Health::getStatus)                .collect(Collectors.toList());        Status status = aggregateStatus(statusCandidates);        Map details = aggregateDetails(healths);return new Health.Builder(status, details).build();    }
protected Status aggregateStatus(List candidates) {// Only sort those status instances that we know about        List filteredCandidates = new ArrayList<>();for (Status candidate : candidates) {if (this.statusOrder.contains(candidate.getCode())) {                filteredCandidates.add(candidate);            }        }// If no status is given return UNKNOWNif (filteredCandidates.isEmpty()) {return Status.UNKNOWN;        }// Sort given Status instances by configured order        filteredCandidates.sort(new StatusComparator(this.statusOrder));return filteredCandidates.get(0);    }
private class StatusComparator implements Comparator {private final List statusOrder;        StatusComparator(List statusOrder) {this.statusOrder = statusOrder;        }@Overridepublic int compare(Status s1, Status s2) {int i1 = this.statusOrder.indexOf(s1.getCode());int i2 = this.statusOrder.indexOf(s2.getCode());return (i1 < i2) ? -1 : (i1 != i2) ? 1 : s1.getCode().compareTo(s2.getCode());        }    }}

CompositeHealthIndicator的health是遍歷所有HealthIndicator，調(diào)用HealthIndicator的健康監(jiān)測health方法獲取status。再將status根據(jù)DOWN->OUT_OF_SERVICE->UP->UNKNOWN的順序排序并獲取第一個狀態(tài)（如果有例程狀態(tài)為DOWN，那獲取的結(jié)果就是DOWN）。

public class EurekaHealthCheckHandler implements HealthCheckHandler, ApplicationContextAware, InitializingBean {private static final Map STATUS_MAPPING =new HashMap() {{                put(Status.UNKNOWN, InstanceStatus.UNKNOWN);                put(Status.OUT_OF_SERVICE, InstanceStatus.OUT_OF_SERVICE);                put(Status.DOWN, InstanceStatus.DOWN);                put(Status.UP, InstanceStatus.UP);            }};
protected InstanceStatus mapToInstanceStatus(Status status) {if (!STATUS_MAPPING.containsKey(status)) {return InstanceStatus.UNKNOWN;        }return STATUS_MAPPING.get(status);    }}

最后將通用狀態(tài)STATUS映射成Eureka的例程實例狀態(tài)InstanceStatus，并修改自身的狀態(tài)。

總結(jié)

Eureka-client通過接通本節(jié)能所有的HealthIndicator的health方法對應(yīng)電子雜志的健康檢查狀態(tài)，有如果HealthIndicator檢測查詢查詢結(jié)果為DOWN，那Eureka-client就會判定當(dāng)前服務(wù)有問題，是不可用的，就會將自身狀態(tài)設(shè)置為DOWN，并上報給Eureka-server。Eureka-server收到信息之后將該節(jié)點狀態(tài)標(biāo)識為DOWN，這樣其他服務(wù)就無法從Eureka-server獲取到該計數(shù)器。

本次事故的原因就是因為DataSourceHealthIndicator檢查的結(jié)果是DOWN，導(dǎo)致Eureka-client的狀態(tài)也有所改變DOWN。

擴(kuò)展

1. 如果項目有某個重要的功能，一旦這個功能出問題就希望能將當(dāng)前例程下線，那就可以添加自定義HealthIndicator類，并在health方法檢查改功能是否正常。
2. 可以通過接口+HealthIndicator實現(xiàn)控制服務(wù)上下線：

@RestController@RequestMapping("/healthIndicator")public class MyHealthIndicator implements HealthIndicator {private boolean up;
@GetMapping("setUpVal/{up}")public void setUpVal(@PathVariable("up") boolean up) {this.up = up;    }
@Overridepublic Health health() {if (up) {return Health.up().build();        }return Health.down().build();    }
public MyHealthIndicator setUp(boolean up) {this.up = up;return this;    }}

以上可以通過調(diào)用接口/healthIndicator/setUpVal/false來手動下線當(dāng)前服務(wù)中斷。

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