前言

上一讲eureka client是如何注册的，一直跟到源码发送http请求为止，当时看eureka client注册时如此费尽，光是找一个regiter的地方就找了半天，那么client端发送了http请求给server端，server端是如何处理的呢？

带着这么一个疑问 就开始今天源码的解读了。

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源码解读

从何读起？

上一讲我们知道，跟进client注册 一直到 AbstractJersey2EurekaHttpClient.register方法，这里先看下其中的源码：

public EurekaHttpResponse<Void> register(InstanceInfo info) {
        String urlPath = "apps/" + info.getAppName();
        Response response = null;
        try {
            // 发送请求，类似于：http://localhost:8080/v2/apps/ServiceA
            // 发送的是post请求，服务实例的对象被打成了一个json发送，包括自己的主机、ip、端口号
            // eureka server 就知道了这个ServiceA这个服务，有一个服务实例，比如是在192.168.31.109、host-01、8761端口
            Builder resourceBuilder = jerseyClient.target(serviceUrl).path(urlPath).request();
            addExtraProperties(resourceBuilder);
            addExtraHeaders(resourceBuilder);
            response = resourceBuilder
                    .accept(MediaType.APPLICATION_JSON)
                    .acceptEncoding("gzip")
                    .post(Entity.json(info));
            return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
        } finally {
            if (logger.isDebugEnabled()) {
                logger.debug("Jersey2 HTTP POST {}/{} with instance {}; statusCode={}", serviceUrl, urlPath, info.getId(),
                        response == null ? "N/A" : response.getStatus());
            }
            if (response != null) {
                response.close();
            }
        }
    }

那这种情况我们肯定可以猜测，server端应该有个controller来接收此http请求，然后默默的去做一些注册的逻辑。

紧接着我们从/apps/这个关键词入手，进行全局搜索：

全局搜索结果如下，这里可以看到很多test 调用，这里框起来的一个是不是类似于我们controller接口的调用呢？直接点进去查看，然后一步步跟进。

源码分析

接着上面说的，跟进ApplicationResource这个类，可以找到如下方法：

@Path("{appId}")
public ApplicationResource getApplicationResource(
        @PathParam("version") String version,
        @PathParam("appId") String appId) {
    CurrentRequestVersion.set(Version.toEnum(version));
    return new ApplicationResource(appId, serverConfig, registry);
}

这个appId可以理解为我们之前传递的appName，紧接着这里是直接构造了一个ApplicationResource实例，接着跟进代码，进入ApplicationResource中我们可以看到很多@GET、@POST 等restful接口，还记得上面我们register方法中，发送的http请求用的就是POST方法，所以我们这里直接看@POST请求

@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
    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
    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());
            }
        }
    }

    registry.register(info, "true".equals(isReplication));
    return Response.status(204).build();  // 204 to be backwards compatible
}

由于代码不是很长，这里都给截取出来了。其实这里做的事情就很简单了。

1. 做一些常规的chek，检查注册实例InstanceInfo的一些基本信息
2. DataCenter的相关操作，这里还涉及到亚马逊云，我们直接跳过
3. registry.register(info, "true".equals(isReplication)); 这里才是核心的注册，我们继续往下

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);
    replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}

public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
    try {
        read.lock();
        Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
        REGISTER.increment(isReplication);
        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;
            }
        }
        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");
        }
        Lease<InstanceInfo> lease = new Lease<InstanceInfo>(registrant, leaseDuration);
        if (existingLease != null) {
            lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
        }
        gMap.put(registrant.getId(), lease);
        synchronized (recentRegisteredQueue) {
            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();
        }
        registrant.setActionType(ActionType.ADDED);
        recentlyChangedQueue.add(new RecentlyChangedItem(lease));
        registrant.setLastUpdatedTimestamp();
        invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
        logger.info("Registered instance {}/{} with status {} (replication={})",
                registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication);
    } finally {
        read.unlock();
    }
}

到了这里东西就有点多了，我们慢慢梳理。

1. reda.lock() 这里使用的是读锁，方便多个服务实例同时来注册
2. 这里关键信息是registry的数据结构，同时这也是保存注册实例的对象。

private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry
            = new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>();

ConcurrentHashMap的key是appName
第二层Map的key是appId，所以数据结构格式类似于：

{
    “ServiceA”: {
        “001”: Lease<InstanceInfo>,
        “002”: Lease<InstanceInfo>,
        “003”: Lease<InstanceInfo>
    },
    “ServiceB”: {
        “001”: Lease<InstanceInfo>
    }
}

1. 这里面还有两个队列recentRegisteredQueue、recentlyChangedQueue，其中registerQueue默认保存最近1000条注册的实例信息。
2. 后面就是一些状态设置之类的操作

注册表使用场景

我们注册完成之后，打开eureka 后台配置页面，可以看到自己的实例已经在页面上了，那么这个东东是如何展示的呢？

我们都知道eureka-resources模块下有很多jsp信息，点开status.jsp查看一下：

这里用到了 serverContext.getRegistry().getSortedApplications(), 然后在通过获取的Applicaiton 去执行app.getInstances()等到了所有大的服务实例信息。

这里我们还需要回头看下EurekaBootStrap中的代码，看看Application是如何来的。

从PeerAwareInstanceRegistryImpl.java的getSortedApplications()一直跟到 AbstractInstanceRegistry.java的getApplicationsFromMultipleRegions(),如下图所示：

看到这里是不是就真相大白了？
这里再总结一下：

在jsp代码中，拿到了EurekaServerContext，所以之前为什么要将这个东东放到一个Holder里面去，就是随时都要从这个里面去获取一些数据

然后会从EurekaServerContext，获取到注册表，PeerAwareInstanceRegistry，注册表，从里面获取所有的服务信息，从底层的map数据结构中，获取所有的服务注册的信息，遍历，封装到一个叫Application的东西里去，一个Application就代表了一个服务，里面包含很多个服务实例。

Eureka的服务注册流程图

申明

本文章首发自本人博客：https://www.cnblogs.com/wang-meng 和公众号：壹枝花算不算浪漫，如若转载请标明来源!

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