Eureka系列(二) 服务注册Server端具体实现

服务注册 Server端流程

  我们先看下面这张图片，这张图片简单描述了下我们EurekaClient 在调用EurekaServer 提供的服务注册Http接口，Server端实现接口执行的大致流程如下，图中还包含了获取服务的大致流程。

服务注册Server端实现源码分析

   接下来我们看看Client在调用Server端提供的注册接口的具体实现，注册接口是Server端ApplicationResource类addInstance方法实现，下面我们来看看这个方法：

@POST
@Consumes({"application/json", "application/xml"})
public Response addInstance(InstanceInfo info,
                            @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    logger.debug("Registering instance {} (replication={})", info.getId(), isReplication);
    // validate that the instanceinfo contains all the necessary required fields
    // 参数校验
    if (isBlank(info.getId())) {
        return Response.status(400).entity("Missing instanceId").build();
    } else if (isBlank(info.getHostName())) {
        return Response.status(400).entity("Missing hostname").build();
    } else if (isBlank(info.getIPAddr())) {
        return Response.status(400).entity("Missing ip address").build();
    } else if (isBlank(info.getAppName())) {
        return Response.status(400).entity("Missing appName").build();
    } else if (!appName.equals(info.getAppName())) {
        return Response.status(400).entity("Mismatched appName, expecting " + appName + " but was " + info.getAppName()).build();
    } else if (info.getDataCenterInfo() == null) {
        return Response.status(400).entity("Missing dataCenterInfo").build();
    } else if (info.getDataCenterInfo().getName() == null) {
        return Response.status(400).entity("Missing dataCenterInfo Name").build();
    }
    // handle cases where clients may be registering with bad DataCenterInfo with missing data
    // 处理客户端可能注册错误的DataCenterInfo而丢失数据的情况
    DataCenterInfo dataCenterInfo = info.getDataCenterInfo();
    if (dataCenterInfo instanceof UniqueIdentifier) {
        String dataCenterInfoId = ((UniqueIdentifier) dataCenterInfo).getId();
        if (isBlank(dataCenterInfoId)) {
            boolean experimental = "true".equalsIgnoreCase(serverConfig.getExperimental("registration.validation.dataCenterInfoId"));
            if (experimental) {
                String entity = "DataCenterInfo of type " + dataCenterInfo.getClass() + " must contain a valid id";
                return Response.status(400).entity(entity).build();
            } else if (dataCenterInfo instanceof AmazonInfo) {
                AmazonInfo amazonInfo = (AmazonInfo) dataCenterInfo;
                String effectiveId = amazonInfo.get(AmazonInfo.MetaDataKey.instanceId);
                if (effectiveId == null) {
                    amazonInfo.getMetadata().put(AmazonInfo.MetaDataKey.instanceId.getName(), info.getId());
                }
            } else {
                logger.warn("Registering DataCenterInfo of type {} without an appropriate id", dataCenterInfo.getClass());
            }
        }
    }
    // 注册方法
    registry.register(info, "true".equals(isReplication));
    return Response.status(204).build();  // 204 to be backwards compatible
}

  我们接着继续看 PeerAwareInstanceRegistryImpl 类中的 register 方法：

@Override
public void register(final InstanceInfo info, final boolean isReplication) {
    int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
    if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
        leaseDuration = info.getLeaseInfo().getDurationInSecs();
    }
    super.register(info, leaseDuration, isReplication);
    // 向其他Server同步服务注册消息
    replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}

  我们接着继续看 AbstractInstanceRegistry 类中的 register 方法：

public abstract class AbstractInstanceRegistry implements InstanceRegistry {
    // 实例信息
    private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry = new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>();
    public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
    try {
        read.lock();
        // 从本地MAP里面获取当前实例的信息
        Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
        REGISTER.increment(isReplication);
        // 判断该服务是不是第一次进来，也就是gMap为空，则创建一个ConcurrentHashMap放入到registry里面去
        if (gMap == null) {
            final ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap = new ConcurrentHashMap<String, Lease<InstanceInfo>>();
            gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap);
            if (gMap == null) {
                gMap = gNewMap;
            }
        }
        // 从MAP中查询已经存在的Lease信息 （比如第二次来）
        Lease<InstanceInfo> existingLease = gMap.get(registrant.getId());
        // Retain the last dirty timestamp without overwriting it, if there is already a lease
        if (existingLease != null && (existingLease.getHolder() != null)) {
            Long existingLastDirtyTimestamp = existingLease.getHolder().getLastDirtyTimestamp();
            Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();
            logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);

            // this is a > instead of a >= because if the timestamps are equal, we still take the remote transmitted
            // InstanceInfo instead of the server local copy.
            if (existingLastDirtyTimestamp > registrationLastDirtyTimestamp) {
                logger.warn("There is an existing lease and the existing lease's dirty timestamp {} is greater" +
                        " than the one that is being registered {}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
                logger.warn("Using the existing instanceInfo instead of the new instanceInfo as the registrant");
                registrant = existingLease.getHolder();
            }
        } else {
            // The lease does not exist and hence it is a new registration
            synchronized (lock) {
                if (this.expectedNumberOfRenewsPerMin > 0) {
                    // Since the client wants to cancel it, reduce the threshold
                    // (1
                    // for 30 seconds, 2 for a minute)
                    this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin + 2;
                    this.numberOfRenewsPerMinThreshold =
                            (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
                }
            }
            logger.debug("No previous lease information found; it is new registration");
        }
        // 构建一个最新的Lease信息
        Lease<InstanceInfo> lease = new Lease<InstanceInfo>(registrant, leaseDuration);
        if (existingLease != null) {
             // 当原来存在Lease的信息时，设置他的serviceUpTimestamp, 保证服务开启的时间一直是第一次的那个。
            lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
        }
        gMap.put(registrant.getId(), lease);
        synchronized (recentRegisteredQueue) {
            // 添加到最近的注册队列里面去，以时间戳作为Key， 名称作为value，主要是为了运维界面的统计数据。
            recentRegisteredQueue.add(new Pair<Long, String>(
                    System.currentTimeMillis(),
                    registrant.getAppName() + "(" + registrant.getId() + ")"));
        }

        // This is where the initial state transfer of overridden status happens
        if (!InstanceStatus.UNKNOWN.equals(registrant.getOverriddenStatus())) {
            logger.debug("Found overridden status {} for instance {}. Checking to see if needs to be add to the "
                            + "overrides", registrant.getOverriddenStatus(), registrant.getId());
            if (!overriddenInstanceStatusMap.containsKey(registrant.getId())) {
                logger.info("Not found overridden id {} and hence adding it", registrant.getId());
                overriddenInstanceStatusMap.put(registrant.getId(), registrant.getOverriddenStatus());
            }
        }

        InstanceStatus overriddenStatusFromMap = overriddenInstanceStatusMap.get(registrant.getId());
        if (overriddenStatusFromMap != null) {
            logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
            registrant.setOverriddenStatus(overriddenStatusFromMap);
        }

        // Set the status based on the overridden status rules
        InstanceStatus overriddenInstanceStatus = getOverriddenInstanceStatus(registrant, existingLease, isReplication);
        registrant.setStatusWithoutDirty(overriddenInstanceStatus);

        // If the lease is registered with UP status, set lease service up timestamp
        if (InstanceStatus.UP.equals(registrant.getStatus())) {
            lease.serviceUp();
        }
        // 设置注册类型为添加
        registrant.setActionType(ActionType.ADDED);
        // 租约变更记录队列，记录了实例的每次变化， 用于注册信息的增量获取、
        recentlyChangedQueue.add(new RecentlyChangedItem(lease));（重要）
        registrant.setLastUpdatedTimestamp();
        // 清理缓存（读写缓存）
        invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
        logger.info("Registered instance {}/{} with status {} (replication={})",
                registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication);
    } finally {
        read.unlock();
    }
}

  总结一下服务的注册流程，大致为以下几步：

     \(\color{red}{1.保存服务实例信息}\)

     \(\color{red}{2.将添加的服务信息存进变更队列，方面实例信息的增量获取}\)

     \(\color{red}{3.清理缓存数据(读写缓存) }\) （注意：此处会清理读写缓存）

     \(\color{red}{4.向其他Server同步服务注册消息}\)