承接上文的對應的Eureka的上篇介紹，我們開始介紹，詳見 [【SpringCloud技術專題】「Eureka源碼分析」從源碼層面讓你認識Eureka工作流程和運作機制（上）]
原理回顧
- Eureka Server 提供服務注冊服務，各個節點啟動后，會在Eureka Server中進行注冊，這樣Eureka Server中的服務注冊表中將會存儲所有可用服務節點的信息，服務節點的信息可以在界面中直觀的看到。
- Eureka Client 是一個Java 客戶端，用于簡化與Eureka Server的交互，客戶端同時也具備一個內置的、使用輪詢負載算法的負載均衡器。
- 在應用啟動后，將會向Eureka Server發送心跳(默認周期為30秒)，如果Eureka Server在多個心跳周期（默認3個心跳周期=90秒）沒有收到某個節點的心跳，Eureka Server將會從服務注冊表中把這個服務節點移除。
- 高可用情況下的：Eureka Server之間將會通過復制的方式完成數據的同步；
- Eureka Client具有緩存的機制，即使所有的Eureka Server 都掛掉的話，客戶端依然可以利用緩存中的信息消費其它服務的API；
EurekaServer 啟動流程分析
EurekaServer 處理服務注冊、集群數據復制
EurekaClient 是如何注冊到 EurekaServer 的？
剛才在org.springframework.cloud.netflix.eureka.server.InstanceRegistry 的每個方法都打了一個斷點，而且現在EurekaServer已經處于Debug運行狀態，那么我們就隨便找一個被 @EnableEurekaClient 的微服務啟動試試微服務來試試吧，直接Run。
- 當啟動后，就一定會調用注冊register方法，那么就接著往下看，拭目以待；
實例注冊方法機制
InstanceRegistry.register(final InstanceInfo info, final boolean isReplication) 方法進斷點了。
- InstanceRegistry.register順著堆棧信息往上看，是 ApplicationResource.addInstance 方法被調用了，分析addInstance；
ApplicationResource 類
主要是處理接收 Http 的服務請求。
@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.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
}
這里的寫法貌似看起來和我們之前 Controller 的 RESTFUL 寫法有點不一樣，仔細一看，原來是Jersey RESTful 框架，是一個產品級的RESTful service 和 client 框架。與Struts類似，它同樣可以和hibernate,spring框架整合。
看到 registry.register(info, "true".equals(isReplication)); 注冊啊，原來EurekaClient客戶端啟動后會調用會通過Http(s)請求，直接調到ApplicationResource.addInstance 方法，只要是和注冊有關的，都會調用這個方法。
接著我們深入 registry.register(info, "true".equals(isReplication)) 查看；
@Override
public void register(final InstanceInfo info, final boolean isReplication) {
handleRegistration(info, resolveInstanceLeaseDuration(info), isReplication);
super.register(info, isReplication);
}
- handleRegistration(info, resolveInstanceLeaseDuration(info), isReplication) 方法；
private void handleRegistration(InstanceInfo info, int leaseDuration,
boolean isReplication) {
log("register " + info.getAppName() + ", vip " + info.getVIPAddress()
+ ", leaseDuration " + leaseDuration + ", isReplication "
+ isReplication);
publishEvent(new EurekaInstanceRegisteredEvent(this, info, leaseDuration,
isReplication));
}
- 然后通過 ApplicationContext 發布了一個事件 EurekaInstanceRegisteredEvent 服務注冊事件，可以給 EurekaInstanceRegisteredEvent 添加監聽事件，那么用戶就可以在此刻實現自己想要的一些業務邏輯。
- 然后我們再來看看 super.register(info, isReplication) 方法，該方法是 InstanceRegistry 的父類 PeerAwareInstanceRegistryImpl 的方法。
服務戶廁機制
進入PeerAwareInstanceRegistryImpl 類的 register(final InstanceInfo info, final boolean isReplication) 方法；
@Override
public void register(final InstanceInfo info, final boolean isReplication) {
// 注釋：續約時間，默認時間是常量值 90 秒
int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
// 注釋：續約時間，當然也可以從配置文件中取出來，所以說續約時間值也是可以讓我們自己自定義配置的
if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
leaseDuration = info.getLeaseInfo().getDurationInSecs();
}
// 注釋：將注冊方的信息寫入 EurekaServer 的注冊表，父類為 AbstractInstanceRegistry
super.register(info, leaseDuration, isReplication);
// 注釋：EurekaServer 節點之間的數據同步，復制到其他Peer
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}
進入super.register(info, leaseDuration, isReplication)，如何寫入EurekaServer 的注冊表的，進入AbstractInstanceRegistry.register(InstanceInfo registrant, int leaseDuration, boolean isReplication) 方法。
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
try {
read.lock();
// 注釋：registry 這個變量，就是我們所謂的注冊表，注冊表是保存在內存中的；
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);
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();
}
}
- 發現這個方法有點長，大致閱讀，主要更新了注冊表的時間之外，還更新了緩存等其它東西，大家有興趣的可以深究閱讀該方法；
集群之間的復制
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication) 的這個方法。
private void replicateToPeers(Action action, String appName, String id,
InstanceInfo info /* optional */,
InstanceStatus newStatus /* optional */, boolean isReplication) {
Stopwatch tracer = action.getTimer().start();
try {
if (isReplication) {
numberOfReplicationsLastMin.increment();
}
// If it is a replication already, do not replicate again as this will create a poison replication
// 注釋：如果已經復制過，就不再復制
if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
return;
}
// 遍歷Eureka Server集群中的所有節點，進行復制操作
for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
// If the url represents this host, do not replicate to yourself.
if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
continue;
}
// 沒有復制過，遍歷Eureka Server集群中的node節點，依次操作，包括取消、注冊、心跳、狀態更新等。
replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
}
} finally {
tracer.stop();
}
}
每當有注冊請求，首先更新 EurekaServer 的注冊表，然后再將信息同步到其它EurekaServer的節點上去；
接下來我們看看 node 節點是如何進行復制操作的，進入 replicateInstanceActionsToPeers 方法。
private void replicateInstanceActionsToPeers(Action action, String appName,
String id, InstanceInfo info, InstanceStatus newStatus,
PeerEurekaNode node) {
try {
InstanceInfo infoFromRegistry = null;
CurrentRequestVersion.set(Version.V2);
switch (action) {
case Cancel:
node.cancel(appName, id);
break;
case Heartbeat:
InstanceStatus overriddenStatus = overriddenInstanceStatusMap.get(id);
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.heartbeat(appName, id, infoFromRegistry, overriddenStatus, false);
break;
case Register:
node.register(info);
break;
case StatusUpdate:
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.statusUpdate(appName, id, newStatus, infoFromRegistry);
break;
case DeleteStatusOverride:
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.deleteStatusOverride(appName, id, infoFromRegistry);
break;
}
} catch (Throwable t) {
logger.error("Cannot replicate information to {} for action {}", node.getServiceUrl(), action.name(), t);
}
}
- 節點之間的復制狀態操作，都在這里體現的淋漓盡致，那么我們就拿 Register 類型 node.register(info) 來看，我們來看看 node 究竟是如何做到同步信息的，進入 node.register(info) 方法看看；
同級之間的復制機制
PeerEurekaNode.register(final InstanceInfo info) 方法，一窺究竟如何同步數據。
public void register(final InstanceInfo info) throws Exception {
// 注釋：任務過期時間給任務分發器處理，默認時間偏移當前時間 30秒
long expiryTime = System.currentTimeMillis() + getLeaseRenewalOf(info);
batchingDispatcher.process(
taskId("register", info),
new InstanceReplicationTask(targetHost, Action.Register, info, null, true) {
public EurekaHttpResponse<Void> execute() {
return replicationClient.register(info);
}
},
expiryTime
);
}
這里涉及到了 Eureka 的任務批處理，通常情況下Peer之間的同步需要調用多次，如果EurekaServer一多的話，那么將會有很多http請求，所
以自然而然的孕育出了任務批處理，但是也在一定程度上導致了注冊和下線的一些延遲，突出優勢的同時也勢必會造成一些劣勢，但是這些延遲情況還是能符合
常理在容忍范圍之內的。在 expiryTime 超時時間之內，批次處理要做的事情就是合并任務為一個List，然后發送請求的時候，將這個批次List直接打包發送請求出去，這樣的話，在這個批次的List里面，可能包含取消、注冊、心跳、狀態等一系列狀態的集合List。
我們再接著看源碼，batchingDispatcher.process 這么一調用，然后我們就直接看這個 TaskDispatchers.createBatchingTaskDispatcher 方法。
public static <ID, T> TaskDispatcher<ID, T> createBatchingTaskDispatcher(String id,
int maxBufferSize,
int workloadSize,
int workerCount,
long maxBatchingDelay,
long congestionRetryDelayMs,
long networkFailureRetryMs,
TaskProcessor<T> taskProcessor) {
final AcceptorExecutor<ID, T> acceptorExecutor = new AcceptorExecutor<>(
id, maxBufferSize, workloadSize, maxBatchingDelay, congestionRetryDelayMs, networkFailureRetryMs
);
final TaskExecutors<ID, T> taskExecutor = TaskExecutors.batchExecutors(id, workerCount, taskProcessor, acceptorExecutor);
return new TaskDispatcher<ID, T>() {
@Override
public void process(ID id, T task, long expiryTime) {
acceptorExecutor.process(id, task, expiryTime);
}
@Override
public void shutdown() {
acceptorExecutor.shutdown();
taskExecutor.shutdown();
}
};
}
- 這里的 process 方法會將任務添加到隊列中，有入隊列自然有出隊列，具體怎么取任務，我就不一一給大家講解了，我就講講最后是怎么觸發任務的。進入 final TaskExecutors<ID, T> taskExecutor = TaskExecutors.batchExecutors(id, workerCount, taskProcessor, acceptorExecutor) 這句代碼的 TaskExecutors.batchExecutors 方法。
static <ID, T> TaskExecutors<ID, T> batchExecutors(final String name,
int workerCount,
final TaskProcessor<T> processor,
final AcceptorExecutor<ID, T> acceptorExecutor) {
final AtomicBoolean isShutdown = new AtomicBoolean();
final TaskExecutorMetrics metrics = new TaskExecutorMetrics(name);
return new TaskExecutors<>(new WorkerRunnableFactory<ID, T>() {
@Override
public WorkerRunnable<ID, T> create(int idx) {
return new BatchWorkerRunnable<>("TaskBatchingWorker-" +name + '-' + idx, isShutdown, metrics, processor, acceptorExecutor);
}
}, workerCount, isShutdown);
}
- 我們發現 TaskExecutors 類中的 batchExecutors 這個靜態方法，有個 BatchWorkerRunnable 返回的實現類，因此我們再次進入 BatchWorkerRunnable 類看看究竟,而且既然是 Runnable，那么勢必會有 run 方法。
@Override
public void run() {
try {
while (!isShutdown.get()) {
// 注釋：獲取信號量釋放 batchWorkRequests.release()，返回任務集合列表
List<TaskHolder<ID, T>> holders = getWork();
metrics.registerExpiryTimes(holders);
List<T> tasks = getTasksOf(holders);
// 注釋：將批量任務打包請求Peer節點
ProcessingResult result = processor.process(tasks);
switch (result) {
case Success:
break;
case Congestion:
case TransientError:
taskDispatcher.reprocess(holders, result);
break;
case PermanentError:
logger.warn("Discarding {} tasks of {} due to permanent error", holders.size(), workerName);
}
metrics.registerTaskResult(result, tasks.size());
}
} catch (InterruptedException e) {
// Ignore
} catch (Throwable e) {
// Safe-guard, so we never exit this loop in an uncontrolled way.
logger.warn("Discovery WorkerThread error", e);
}
}
- 這就是我們 BatchWorkerRunnable 類的 run 方法，這里面首先要獲取信號量釋放，才能獲得任務集合，一旦獲取到了任務集合的話，那么就直接調用 processor.process(tasks) 方法請求 Peer 節點同步數據，接下來我們看看 ReplicationTaskProcessor.process 方法；
@Override
public ProcessingResult process(List<ReplicationTask> tasks) {
ReplicationList list = createReplicationListOf(tasks);
try {
// 注釋：這里通過 JerseyReplicationClient 客戶端對象直接發送list請求數據
EurekaHttpResponse<ReplicationListResponse> response = replicationClient.submitBatchUpdates(list);
int statusCode = response.getStatusCode();
if (!isSuccess(statusCode)) {
if (statusCode == 503) {
logger.warn("Server busy (503) HTTP status code received from the peer {}; rescheduling tasks after delay", peerId);
return ProcessingResult.Congestion;
} else {
// Unexpected error returned from the server. This should ideally never happen.
logger.error("Batch update failure with HTTP status code {}; discarding {} replication tasks", statusCode, tasks.size());
return ProcessingResult.PermanentError;
}
} else {
handleBatchResponse(tasks, response.getEntity().getResponseList());
}
} catch (Throwable e) {
if (isNetworkConnectException(e)) {
logNetworkErrorSample(null, e);
return ProcessingResult.TransientError;
} else {
logger.error("Not re-trying this exception because it does not seem to be a network exception", e);
return ProcessingResult.PermanentError;
}
}
return ProcessingResult.Success;
}
- 感覺快要見到真相了，所以我們迫不及待的進入 JerseyReplicationClient.submitBatchUpdates(ReplicationList replicationList) 方法一窺究竟。
@Override
public EurekaHttpResponse<ReplicationListResponse> submitBatchUpdates(ReplicationList replicationList) {
ClientResponse response = null;
try {
response = jerseyApacheClient.resource(serviceUrl)
// 注釋：這才是重點，請求目的相對路徑，peerreplication/batch/
.path(PeerEurekaNode.BATCH_URL_PATH)
.accept(MediaType.APPLICATION_JSON_TYPE)
.type(MediaType.APPLICATION_JSON_TYPE)
.post(ClientResponse.class, replicationList);
if (!isSuccess(response.getStatus())) {
return anEurekaHttpResponse(response.getStatus(), ReplicationListResponse.class).build();
}
ReplicationListResponse batchResponse = response.getEntity(ReplicationListResponse.class);
return anEurekaHttpResponse(response.getStatus(), batchResponse).type(MediaType.APPLICATION_JSON_TYPE).build();
} finally {
if (response != null) {
response.close();
}
}
}
- 看到了相對路徑地址，我們搜索下"batch"這樣的字符串看看有沒有對應的接收方法或者被@Path注解進入的；在 eureka-core-1.4.12.jar 這個包下面，果然搜到到了 @Path("batch") 這樣的字樣，直接進入，發現這是 PeerReplicationResource 類的方法 batchReplication，我們進入這方法看看。
@Path("batch")
@POST
public Response batchReplication(ReplicationList replicationList) {
try {
ReplicationListResponse batchResponse = new ReplicationListResponse();
// 注釋：這里將收到的任務列表，依次循環解析處理，主要核心方法在 dispatch 方法中。
for (ReplicationInstance instanceInfo : replicationList.getReplicationList()) {
try {
batchResponse.addResponse(dispatch(instanceInfo));
} catch (Exception e) {
batchResponse.addResponse(new ReplicationInstanceResponse(Status.INTERNAL_SERVER_ERROR.getStatusCode(), null));
logger.error(instanceInfo.getAction() + " request processing failed for batch item "
+ instanceInfo.getAppName() + '/' + instanceInfo.getId(), e);
}
}
return Response.ok(batchResponse).build();
} catch (Throwable e) {
logger.error("Cannot execute batch Request", e);
return Response.status(Status.INTERNAL_SERVER_ERROR).build();
}
}
- 看到了循環一次遍歷任務進行處理，不知不覺覺得心花怒放，勝利的重點馬上就要到來了，我們進入 PeerReplicationResource.dispatch 方法看看。
private ReplicationInstanceResponse dispatch(ReplicationInstance instanceInfo) {
ApplicationResource applicationResource = createApplicationResource(instanceInfo);
InstanceResource resource = createInstanceResource(instanceInfo, applicationResource);
String lastDirtyTimestamp = toString(instanceInfo.getLastDirtyTimestamp());
String overriddenStatus = toString(instanceInfo.getOverriddenStatus());
String instanceStatus = toString(instanceInfo.getStatus());
Builder singleResponseBuilder = new Builder();
switch (instanceInfo.getAction()) {
case Register:
singleResponseBuilder = handleRegister(instanceInfo, applicationResource);
break;
case Heartbeat:
singleResponseBuilder = handleHeartbeat(resource, lastDirtyTimestamp, overriddenStatus, instanceStatus);
break;
case Cancel:
singleResponseBuilder = handleCancel(resource);
break;
case StatusUpdate:
singleResponseBuilder = handleStatusUpdate(instanceInfo, resource);
break;
case DeleteStatusOverride:
singleResponseBuilder = handleDeleteStatusOverride(instanceInfo, resource);
break;
}
return singleResponseBuilder.build();
}
- 隨便抓一個類型，那我們也拿 Register 類型來看，進入 PeerReplicationResource.handleRegister 看看。
private static Builder handleRegister(ReplicationInstance instanceInfo, ApplicationResource applicationResource) {
// 注釋：private static final String REPLICATION = "true"; 定義的一個常量值，而且還是回調 ApplicationResource.addInstance 方法
applicationResource.addInstance(instanceInfo.getInstanceInfo(), REPLICATION);
return new Builder().setStatusCode(Status.OK.getStatusCode());
}
- Peer節點的同步旅程終于結束了，最終又回調到了 ApplicationResource.addInstance 這個方法，這個方法在最終是EurekaClient啟動后注冊調用的方法，然而Peer節點的信息同步也調用了這個方法，僅僅只是通過一個變量 isReplication 為true還是false來判斷是否是節點復制。剩下的ApplicationResource.addInstance流程前面已經提到過了，相信大家已經明白了注冊的流程是如何扭轉的，包括批量任務是如何處理EurekaServer節點之間的信息同步的了。
EurekaClient 啟動流程分析
調換運行模式
Run運行discovery-eureka服務，Debug 運行 provider-user 服務，先觀察日志先；
2017-10-23 19:43:07.688 INFO 1488 --- [ main] o.s.c.support.DefaultLifecycleProcessor : Starting beans in phase 0
2017-10-23 19:43:07.694 INFO 1488 --- [ main] o.s.c.n.eureka.InstanceInfoFactory : Setting initial instance status as: STARTING
2017-10-23 19:43:07.874 INFO 1488 --- [ main] c.n.d.provider.DiscoveryJerseyProvider : Using JSON encoding codec LegacyJacksonJson
2017-10-23 19:43:07.874 INFO 1488 --- [ main] c.n.d.provider.DiscoveryJerseyProvider : Using JSON decoding codec LegacyJacksonJson
2017-10-23 19:43:07.971 INFO 1488 --- [ main] c.n.d.provider.DiscoveryJerseyProvider : Using XML encoding codec XStreamXml
2017-10-23 19:43:07.971 INFO 1488 --- [ main] c.n.d.provider.DiscoveryJerseyProvider : Using XML decoding codec XStreamXml
2017-10-23 19:43:08.134 INFO 1488 --- [ main] c.n.d.s.r.aws.ConfigClusterResolver : Resolving eureka endpoints via configuration
2017-10-23 19:43:08.344 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Disable delta property : false
2017-10-23 19:43:08.344 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Single vip registry refresh property : null
2017-10-23 19:43:08.344 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Force full registry fetch : false
2017-10-23 19:43:08.344 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Application is null : false
2017-10-23 19:43:08.344 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Registered Applications size is zero : true
2017-10-23 19:43:08.344 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Application version is -1: true
2017-10-23 19:43:08.345 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Getting all instance registry info from the eureka server
2017-10-23 19:43:08.630 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : The response status is 200
2017-10-23 19:43:08.631 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Starting heartbeat executor: renew interval is: 30
2017-10-23 19:43:08.634 INFO 1488 --- [ main] c.n.discovery.InstanceInfoReplicator : InstanceInfoReplicator onDemand update allowed rate per min is 4
2017-10-23 19:43:08.637 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Discovery Client initialized at timestamp 1508758988637 with initial instances count: 0
2017-10-23 19:43:08.657 INFO 1488 --- [ main] c.n.e.EurekaDiscoveryClientConfiguration : Registering application springms-provider-user with eureka with status UP
2017-10-23 19:43:08.658 INFO 1488 --- [ main] com.netflix.discovery.DiscoveryClient : Saw local status change event StatusChangeEvent [timestamp=1508758988658, current=UP, previous=STARTING]
2017-10-23 19:43:08.659 INFO 1488 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient : DiscoveryClient_SPRINGMS-PROVIDER-USER/springms-provider-user:192.168.3.101:7900: registering service...
2017-10-23 19:43:08.768 INFO 1488 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 7900 (http)
2017-10-23 19:43:08.768 INFO 1488 --- [ main] c.n.e.EurekaDiscoveryClientConfiguration : Updating port to 7900
2017-10-23 19:43:08.773 INFO 1488 --- [ main] c.s.cloud.MsProviderUserApplication : Started ProviderApplication in 882.1 seconds (JVM running for 10.398)
服務提供方主體加載流程
【1】：仔細查看下日志，先是 DefaultLifecycleProcessor 類處理了一些 bean,然后接下來肯定會調用一些實現 SmartLifecycle 類的start 方法；
【2】： 接著初始化設置了EurekaClient的狀態為 STARTING，初始化編碼使用的格式，哪些用JSON，哪些用XML；
【3】： 緊接著打印了強制獲取注冊信息狀態為false，已注冊的應用大小為0，客戶端發送心跳續約，心跳續約間隔為30秒，最后打印Client初始化完成；
EnableEurekaClient 組件。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@EnableDiscoveryClient
public @interface EnableEurekaClient {}
@EnableEurekaClient
這個注解類竟然也使用了注解 @EnableDiscoveryClient，那么我們有必要去這個注解類看看。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {}
@EnableDiscoveryClient
這個注解類有個比較特殊的注解 @Import，由此我們猜想，這里的大多數邏輯是不是都寫在這個 EnableDiscoveryClientImportSelector 類呢？
EnableDiscoveryClientImportSelector
@Order(Ordered.LOWEST_PRECEDENCE - 100)
public class EnableDiscoveryClientImportSelector
extends SpringFactoryImportSelector<EnableDiscoveryClient> {
@Override
protected boolean isEnabled() {
return new RelaxedPropertyResolver(getEnvironment()).getProperty(
"spring.cloud.discovery.enabled", Boolean.class, Boolean.TRUE);
}
@Override
protected boolean hasDefaultFactory() {
return true;
}
}
EnableDiscoveryClientImportSelector 類繼承了 SpringFactoryImportSelector 類，但是重寫了一個 isEnabled() 方法，默認值返回 true，為什么會返回true。
/**
* Select and return the names of which class(es) should be imported based on
* the {@link AnnotationMetadata} of the importing @{@link Configuration} class.
*/
@Override
public String[] selectImports(AnnotationMetadata metadata) {
if (!isEnabled()) {
return new String[0];
}
AnnotationAttributes attributes = AnnotationAttributes.fromMap(
metadata.getAnnotationAttributes(this.annotationClass.getName(), true));
Assert.notNull(attributes, "No " + getSimpleName() + " attributes found. Is "
+ metadata.getClassName() + " annotated with @" + getSimpleName() + "?");
// Find all possible auto configuration classes, filtering duplicates
List<String> factories = new ArrayList<>(new LinkedHashSet<>(SpringFactoriesLoader
.loadFactoryNames(this.annotationClass, this.beanClassLoader)));
if (factories.isEmpty() && !hasDefaultFactory()) {
throw new IllegalStateException("Annotation @" + getSimpleName()
+ " found, but there are no implementations. Did you forget to include a starter?");
}
if (factories.size() > 1) {
// there should only ever be one DiscoveryClient, but there might be more than
// one factory
log.warn("More than one implementation " + "of @" + getSimpleName()
+ " (now relying on @Conditionals to pick one): " + factories);
}
return factories.toArray(new String[factories.size()]);
}
EnableDiscoveryClientImportSelector.selectImports
首先通過注解獲取了一些屬性，然后加載了一些類名稱，我們進入loadFactoryNames 方法看看。
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
// 注釋：public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
// 注釋：這個 jar 包下的一個配置文件
Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
List<String> result = new ArrayList<String>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
"] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
加載了一個配置文件，配置文件里面寫了啥呢？打開SpringFactoryImportSelector該文件所在的jar包的spring.factories文件一看。
# AutoConfiguration
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.client.CommonsClientAutoConfiguration,\
org.springframework.cloud.client.discovery.noop.NoopDiscoveryClientAutoConfiguration,\
org.springframework.cloud.client.hypermedia.CloudHypermediaAutoConfiguration,\
org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration,\
org.springframework.cloud.commons.util.UtilAutoConfiguration
# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.cloud.client.HostInfoEnvironmentPostProcessor
都是一些 Configuration 后綴的類名，所以這些都是加載的一堆堆的配置文件類。
factories對象里面只有一個類名路徑為 org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration 。
EurekaDiscoveryClientConfiguration
@Configuration
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@CommonsLog
public class EurekaDiscoveryClientConfiguration implements SmartLifecycle, Ordered {
@Override
public void start() {
// only set the port if the nonSecurePort is 0 and this.port != 0
if (this.port.get() != 0 && this.instanceConfig.getNonSecurePort() == 0) {
this.instanceConfig.setNonSecurePort(this.port.get());
}
// only initialize if nonSecurePort is greater than 0 and it isn't already running
// because of containerPortInitializer below
if (!this.running.get() && this.instanceConfig.getNonSecurePort() > 0) {
maybeInitializeClient();
if (log.isInfoEnabled()) {
log.info("Registering application " + this.instanceConfig.getAppname()
+ " with eureka with status "
+ this.instanceConfig.getInitialStatus());
}
this.applicationInfoManager
.setInstanceStatus(this.instanceConfig.getInitialStatus());
if (this.healthCheckHandler != null) {
this.eurekaClient.registerHealthCheck(this.healthCheckHandler);
}
this.context.publishEvent(
new InstanceRegisteredEvent<>(this, this.instanceConfig));
this.running.set(true);
}
}
｝
- 首先看到該類實現了SmartLifecycle 接口，那么就肯定會實現 start 方法，而且這個 start 方法感覺應在會被加載執行的。
this.applicationInfoManager.setInstanceStatus(this.instanceConfig.getInitialStatus()) 這段代碼有一個觀察者模式的回調存在。
// ApplicationInfoManager.setInstanceStatus 的方法
public synchronized void setInstanceStatus(InstanceStatus status) {// 打上斷點
InstanceStatus prev = instanceInfo.setStatus(status);
if (prev != null) {
for (StatusChangeListener listener : listeners.values()) {
try {
listener.notify(new StatusChangeEvent(prev, status));
} catch (Exception e) {
logger.warn("failed to notify listener: {}", listener.getId(), e);
}
}
}
}
這個方法會因為狀態的改變而回調所有實現 StatusChangeListener 這個類的地方，前提得先注冊到 listeners 中去才行。
于是乎，我們斷定，若想要回調，那么就必須有地方先注冊這個事件，而且這個注冊還必須提前執行在 start 方法前執行，于是我們得先在ApplicationInfoManager 這個類中找到注冊到 listeners 的這個方法。
public void registerStatusChangeListener(StatusChangeListener listener) {// 打上斷點
listeners.put(listener.getId(), listener);
}
于是我們逆向找下 registerStatusChangeListener 被調用的地方。
很不巧的是，盡然只有1個地方被調用，這個地方就是 DiscoveryClient.initScheduledTasks 方法，而且 initScheduledTasks
方法又是在 DiscoveryClient 的構造函數里面調用的，同時我們也對 initScheduledTasks 以及 initScheduledTasks 被調用的構造方法地方
打上斷點。
果不其然，EurekaDiscoveryClientConfiguration.start 方法被調用了，緊接著 this.applicationInfoManager.setInstanceStatus(this.instanceConfig.getInitialStatus()) 也進入斷點，然后在往下走，又進入的
DiscoveryClient.initScheduledTasks 方法中的 notify 回調處。
- 看著斷點依次經過我們上述分析的地方，然后也符合日志打印的順序，所以我們現在應該是有必要好好看看 DiscoveryClient.initScheduledTasks 這個方法究竟干了什么偉大的事情。然而又想了想，還不如看看 initScheduledTasks 被調用的構造方法。
DiscoveryClient 經過 @Inject 注解過的構造方法。
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, DiscoveryClientOptionalArgs args, Provider<BackupRegistry> backupRegistryProvider) {
if (args != null) {
this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
this.eventListeners.addAll(args.getEventListeners());
} else {
this.healthCheckCallbackProvider = null;
this.healthCheckHandlerProvider = null;
}
this.applicationInfoManager = applicationInfoManager;
InstanceInfo myInfo = applicationInfoManager.getInfo();
clientConfig = config;
staticClientConfig = clientConfig;
transportConfig = config.getTransportConfig();
instanceInfo = myInfo;
if (myInfo != null) {
appPathIdentifier = instanceInfo.getAppName() + "/" + instanceInfo.getId();
} else {
logger.warn("Setting instanceInfo to a passed in null value");
}
this.backupRegistryProvider = backupRegistryProvider;
this.urlRandomizer = new EndpointUtils.InstanceInfoBasedUrlRandomizer(instanceInfo);
localRegionApps.set(new Applications());
fetchRegistryGeneration = new AtomicLong(0);
remoteRegionsToFetch = new AtomicReference<String>(clientConfig.fetchRegistryForRemoteRegions());
remoteRegionsRef = new AtomicReference<>(remoteRegionsToFetch.get() == null ? null : remoteRegionsToFetch.get().split(","));
if (config.shouldFetchRegistry()) {
this.registryStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRY_PREFIX + "lastUpdateSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
} else {
this.registryStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
}
if (config.shouldRegisterWithEureka()) {
this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
} else {
this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
}
if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
logger.info("Client configured to neither register nor query for data.");
scheduler = null;
heartbeatExecutor = null;
cacheRefreshExecutor = null;
eurekaTransport = null;
instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), clientConfig.getRegion());
// This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
// to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
DiscoveryManager.getInstance().setEurekaClientConfig(config);
initTimestampMs = System.currentTimeMillis();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
return; // no need to setup up an network tasks and we are done
}
try {
// 注釋：定時任務調度準備
scheduler = Executors.newScheduledThreadPool(3,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
// 注釋：實例化心跳定時任務線程池
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
// 注釋：實例化緩存刷新定時任務線程池
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
eurekaTransport = new EurekaTransport();
scheduleServerEndpointTask(eurekaTransport, args);
AzToRegionMapper azToRegionMapper;
if (clientConfig.shouldUseDnsForFetchingServiceUrls()) {
azToRegionMapper = new DNSBasedAzToRegionMapper(clientConfig);
} else {
azToRegionMapper = new PropertyBasedAzToRegionMapper(clientConfig);
}
if (null != remoteRegionsToFetch.get()) {
azToRegionMapper.setRegionsToFetch(remoteRegionsToFetch.get().split(","));
}
instanceRegionChecker = new InstanceRegionChecker(azToRegionMapper, clientConfig.getRegion());
} catch (Throwable e) {
throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
}
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
// 注釋：初始化調度任務
initScheduledTasks();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register timers", e);
}
// This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
// to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
DiscoveryManager.getInstance().setEurekaClientConfig(config);
initTimestampMs = System.currentTimeMillis();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
}
- 從往下看，initScheduledTasks 這個方法顧名思義就是初始化調度任務，所以這里面的內容應該就是重頭戲，進入看看。
private void initScheduledTasks() {
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
// 注釋：間隔多久去拉取服務注冊信息，默認時間 30秒
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
// 注釋：定時任務，每間隔 30秒 去拉取一次服務注冊信息
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
if (clientConfig.shouldRegisterWithEureka()) {
// 注釋：間隔多久發送一次心跳續約，默認間隔時間 30 秒
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
// Heartbeat timer
// 注釋：定時任務，每間隔 30秒 去想 EurekaServer 發送一次心跳續約
scheduler.schedule(
new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()
),
renewalIntervalInSecs, TimeUnit.SECONDS);
// InstanceInfo replicator
// 注釋：實例信息復制器，定時刷新dataCenterInfo數據中心信息，默認30秒
instanceInfoReplicator = new InstanceInfoReplicator(
this,
instanceInfo,
clientConfig.getInstanceInfoReplicationIntervalSeconds(),
2); // burstSize
// 注釋：實例化狀態變化監聽器
statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
@Override
public String getId() {
return "statusChangeListener";
}
@Override
public 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);
}
// 注釋：狀態有變化的話，會回調這個方法
instanceInfoReplicator.onDemandUpdate();
}
};
// 注釋：注冊狀態變化監聽器
if (clientConfig.shouldOnDemandUpdateStatusChange()) {
applicationInfoManager.registerStatusChangeListener(statusChangeListener);
}
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
} else {
logger.info("Not registering with Eureka server per configuration");
}
}
在這個方法從上往下一路注釋分析下來，干了EurekaClient我們最想知道的一些事情，定時任務獲取注冊信息，定時任務刷新緩存，定時任務心跳續約，定時任務同步數據中心數據，狀態變化監聽回調等。但是唯獨沒看到注冊，這是怎么回事呢？
instanceInfoReplicator.onDemandUpdate() 就是在狀態改變的時候。
public boolean onDemandUpdate() {
if (rateLimiter.acquire(burstSize, allowedRatePerMinute)) {
scheduler.submit(new Runnable() {
@Override
public void run() {
logger.debug("Executing on-demand update of local InstanceInfo");
Future latestPeriodic = scheduledPeriodicRef.get();
if (latestPeriodic != null && !latestPeriodic.isDone()) {
logger.debug("Canceling the latest scheduled update, it will be rescheduled at the end of on demand update");
latestPeriodic.cancel(false);
}
// 注釋：這里進行了實例信息刷新和注冊
InstanceInfoReplicator.this.run();
}
});
return true;
} else {
logger.warn("Ignoring onDemand update due to rate limiter");
return false;
}
}
onDemandUpdate 這個方法，唯獨 InstanceInfoReplicator.this.run() 這個方法還有點用，而且還是 run 方法呢，感情 InstanceInfoReplicator 這個類還是實現了 Runnable 接口？經過查看這個類，還真是實現了 Runnable 接口。
這個方法應該我們要找的注冊所在的地方。
public void run() {
try {
discoveryClient.refreshInstanceInfo();
Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
if (dirtyTimestamp != null) {
discoveryClient.register();
instanceInfo.unsetIsDirty(dirtyTimestamp);
}
} 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);
}
}
- discoveryClient.register() 這個 register 方法，原來注冊方法就是這個。
boolean register() throws Throwable {
logger.info(PREFIX + appPathIdentifier + ": registering service...");
EurekaHttpResponse<Void> httpResponse;
try {
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
} catch (Exception e) {
logger.warn("{} - registration failed {}", PREFIX + appPathIdentifier, e.getMessage(), e);
throw e;
}
if (logger.isInfoEnabled()) {
logger.info("{} - registration status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
}
return httpResponse.getStatusCode() == 204;
}
- 原來調用了 EurekaHttpClient 封裝的客戶端請求對象來進行注冊的，再繼續深探 registrationClient.register 方法，于是我們來到了 AbstractJerseyEurekaHttpClient.register 方法。
@Override
public EurekaHttpResponse<Void> register(InstanceInfo info) {
String urlPath = "apps/" + info.getAppName();
ClientResponse response = null;
try {
Builder resourceBuilder = jerseyClient.resource(serviceUrl).path(urlPath).getRequestBuilder();
addExtraHeaders(resourceBuilder);
response = resourceBuilder
.header("Accept-Encoding", "gzip")
.type(MediaType.APPLICATION_JSON_TYPE)
.accept(MediaType.APPLICATION_JSON)
// 注釋：打包帶上當前應用的所有信息 info
.post(ClientResponse.class, info);
return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
} finally {
if (logger.isDebugEnabled()) {
logger.debug("Jersey HTTP POST {}/{} with instance {}; statusCode={}", serviceUrl, urlPath, info.getId(),
response == null ? "N/A" : response.getStatus());
}
if (response != null) {
response.close();
}
}
}
- 調用的是 Jersey RESTful 框架來進行請求的，然后在 EurekaServer 那邊就會在 ApplicationResource.addInstance 方法接收客戶端的注冊請求，因此我們的 EurekaClient 是如何注冊的就到此為止了。
