最是人间留不住，朱颜辞镜花辞树。这篇文章主要讲述SpringCloud-技术专区-从源码层面让你认识Eureka工作流程和运作机制（下）相关的知识，希望能为你提供帮助。
原理回顾
- Eureka Server 提供服务注册服务，各个节点启动后，会在Eureka Server中进行注册，这样Eureka Server中的服务注册表中将会存储所有可用服务节点的信息，服务节点的信息可以在界面中直观的看到。
- Eureka Client 是一个java 客户端，用于简化与Eureka Server的交互，客户端同时也具备一个内置的、使用轮询负载算法的负载均衡器。
- 在应用启动后，将会向Eureka Server发送心跳(默认周期为30秒)，如果Eureka Server在多个心跳周期（默认3个心跳周期=90秒）没有收到某个节点的心跳，Eureka Server将会从服务注册表中把这个服务节点移除。
- 高可用情况下的：Eureka Server之间将会通过复制的方式完成数据的同步；
- Eureka Client具有缓存的机制，即使所有的Eureka Server 都挂掉的话，客户端依然可以利用缓存中的信息消费其它服务的API；
EurekaServer 处理服务注册、集群数据复制 EurekaClient 是如何注册到 EurekaServer 的？刚才在org.springframework.cloud.netflix.eureka.server.InstanceRegistry 的每个方法都打了一个断点，而且现在EurekaServer已经处于Debug运行状态，那么我们就随便找一个被 @EnableEurekaClient 的微服务启动试试微服务来试试吧，直接Run。
- 当启动后，就一定会调用注册register方法，那么就接着往下看，拭目以待；
InstanceRegistry.register(final InstanceInfo info, final boolean isReplication) 方法进断点了。- InstanceRegistry.register顺着堆栈信息往上看，是 ApplicationResource.addInstance 方法被调用了，分析addInstance；
@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
}- 这里的写法貌似看起来和我们之前 Controller 的 RESTFUL 写法有点不一样，仔细一看，原来是Jersey RESTful 框架，是一个产品级的RESTful service 和 client 框架。与Struts类似，它同样可以和hibernate,spring框架整合。
- 看到 registry.register(info, "
true"
.equals(isReplication));
注册啊，原来EurekaClient客户端启动后会调用会通过Http(s)请求，直接调到ApplicationResource.addInstance 方法，只要是和注册有关的，都会调用这个方法。
- 接着我们深入 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));
}- 然后通过 ApplicationContext 发布了一个事件 EurekaInstanceRegisteredEvent 服务注册事件，可以给 EurekaInstanceRegisteredEvent 添加监听事件，那么用户就可以在此刻实现自己想要的一些业务逻辑。
- 然后我们再来看看 super.register(info, isReplication) 方法，该方法是 InstanceRegistry 的父类 PeerAwareInstanceRegistryImpl 的方法。
@Override
public void register(final InstanceInfo info, final boolean isReplication) {
// 注释：续约时间，默认时间是常量值 90 秒
int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
// 注释：续约时间，当然也可以从配置文件中取出来，所以说续约时间值也是可以让我们自己自定义配置的
if (info.getLeaseInfo() != null &
&
info.getLeaseInfo().getDurationInSecs() >
0) {
leaseDuration = info.getLeaseInfo().getDurationInSecs();
}
// 注释：将注册方的信息写入 EurekaServer 的注册表，父类为 AbstractInstanceRegistry
super.register(info, leaseDuration, isReplication);
// 注释：EurekaServer 节点之间的数据同步，复制到其他Peer
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
try {
read.lock();
// 注释：registry 这个变量，就是我们所谓的注册表，注册表是保存在内存中的；
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();
}
}- 发现这个方法有点长，大致阅读，主要更新了注册表的时间之外，还更新了缓存等其它东西，大家有兴趣的可以深究阅读该方法；
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
// 注释：如果已经复制过，就不再复制
if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
return;
}
// 遍历Eureka Server集群中的所有节点，进行复制操作
for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
// If the url represents this host, do not replicate to yourself.
if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
continue;
}
// 没有复制过，遍历Eureka Server集群中的node节点，依次操作，包括取消、注册、心跳、状态更新等。
replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
}
} finally {
tracer.stop();
}
}- 每当有注册请求，首先更新 EurekaServer 的注册表，然后再将信息同步到其它EurekaServer的节点上去；
- 接下来我们看看 node 节点是如何进行复制操作的，进入 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);
}
}- 节点之间的复制状态操作，都在这里体现的淋漓尽致，那么我们就拿 Register 类型 node.register(info) 来看，我们来看看 node 究竟是如何做到同步信息的，进入 node.register(info) 方法看看；
PeerEurekaNode.register(final InstanceInfo info) 方法，一窥究竟如何同步数据。
public void register(final InstanceInfo info) throws Exception {
// 注释：任务过期时间给任务分发器处理，默认时间偏移当前时间 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
);
}- 这里涉及到了 Eureka 的任务批处理，通常情况下Peer之间的同步需要调用多次，如果EurekaServer一多的话，那么将会有很多http请求，所
以自然而然的孕育出了任务批处理，但是也在一定程度上导致了注册和下线的一些延迟，突出优势的同时也势必会造成一些劣势，但是这些延迟情况还是能符合
常理在容忍范围之内的。
- 在 expiryTime 超时时间之内，批次处理要做的事情就是合并任务为一个List，然后发送请求的时候，将这个批次List直接打包发送请求出去，这样的话，在这个批次的List里面，可能包含取消、注册、心跳、状态等一系列状态的集合List。
- 我们再接着看源码，batchingDispatcher.process 这么一调用，然后我们就直接看这个 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();
}
};
}- 这里的 process 方法会将任务添加到队列中，有入队列自然有出队列，具体怎么取任务，我就不一一给大家讲解了，我就讲讲最后是怎么触发任务的。进入 final TaskExecutors< ID, T> taskExecutor = TaskExecutors.batchExecutors(id, workerCount, taskProcessor, acceptorExecutor) 这句代码的 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);
}- 我们发现 TaskExecutors 类中的 batchExecutors 这个静态方法，有个 BatchWorkerRunnable 返回的实现类，因此我们再次进入 BatchWorkerRunnable 类看看究竟,而且既然是 Runnable，那么势必会有 run 方法。
@Override public void run() { try { while (!isShutdown.get()) { // 注释：获取信号量释放 batchWorkRequests.release()，返回任务集合列表 List< TaskHolder< ID, T> > holders = getWork(); metrics.registerExpiryTimes(holders); List< T> tasks = getTasksOf(holders); // 注释：将批量任务打包请求Peer节点 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); } }
- 这就是我们 BatchWorkerRunnable 类的 run 方法，这里面首先要获取信号量释放，才能获得任务集合，一旦获取到了任务集合的话，那么就直接调用 processor.process(tasks) 方法请求 Peer 节点同步数据，接下来我们看看 ReplicationTaskProcessor.process 方法；
@Override
public ProcessingResult process(List<
ReplicationTask>
tasks) {
ReplicationList list = createReplicationListOf(tasks);
try {
// 注释：这里通过 JerseyReplicationClient 客户端对象直接发送list请求数据
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;
}- 感觉快要见到真相了，所以我们迫不及待的进入 JerseyReplicationClient.submitBatchUpdates(ReplicationList replicationList) 方法一窥究竟。
@Override
public EurekaHttpResponse<
ReplicationListResponse>
submitBatchUpdates(ReplicationList replicationList) {
ClientResponse response = null;
try {
response = jerseyApacheClient.resource(serviceUrl)
// 注释：这才是重点，请求目的相对路径，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();
}
}
}- 看到了相对路径地址，我们搜索下" batch" 这样的字符串看看有没有对应的接收方法或者被@Path注解进入的；在 eureka-core-1.4.12.jar 这个包下面，果然搜到到了 @Path(" batch" ) 这样的字样，直接进入，发现这是 PeerReplicationResource 类的方法 batchReplication，我们进入这方法看看。
@Path("batch")
@POST
public Response batchReplication(ReplicationList replicationList) {
try {
ReplicationListResponse batchResponse = new ReplicationListResponse();
// 注释：这里将收到的任务列表，依次循环解析处理，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();
}
}- 看到了循环一次遍历任务进行处理，不知不觉觉得心花怒放，胜利的重点马上就要到来了，我们进入 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(); }
- 随便抓一个类型，那我们也拿 Register 类型来看，进入 PeerReplicationResource.handleRegister 看看。
private static Builder handleRegister(ReplicationInstance instanceInfo, ApplicationResource applicationResource) {
// 注释：private static final String REPLICATION = "true";
定义的一个常量值，而且还是回调 ApplicationResource.addInstance 方法
applicationResource.addInstance(instanceInfo.getInstanceInfo(), REPLICATION);
return new Builder().setStatusCode(Status.OK.getStatusCode());
}- Peer节点的同步旅程终于结束了，最终又回调到了 ApplicationResource.addInstance 这个方法，这个方法在最终是EurekaClient启动后注册调用的方法，然而Peer节点的信息同步也调用了这个方法，仅仅只是通过一个变量 isReplication 为true还是false来判断是否是节点复制。剩下的ApplicationResource.addInstance流程前面已经提到过了，相信大家已经明白了注册的流程是如何扭转的，包括批量任务是如何处理EurekaServer节点之间的信息同步的了。
2017-10-23 19:43:07.688INFO 1488 --- [main] o.s.c.support.DefaultLifecycleProcessor: Starting beans in phase 0
2017-10-23 19:43:07.694INFO 1488 --- [main] o.s.c.n.eureka.InstanceInfoFactory: Setting initial instance status as: STARTING
2017-10-23 19:43:07.874INFO 1488 --- [main] c.n.d.provider.DiscoveryJerseyProvider: Using JSON encoding codec LegacyJacksonJson
2017-10-23 19:43:07.874INFO 1488 --- [main] c.n.d.provider.DiscoveryJerseyProvider: Using JSON decoding codec LegacyJacksonJson
2017-10-23 19:43:07.971INFO 1488 --- [main] c.n.d.provider.DiscoveryJerseyProvider: Using XML encoding codec XStreamXml
2017-10-23 19:43:07.971INFO 1488 --- [main] c.n.d.provider.DiscoveryJerseyProvider: Using XML decoding codec XStreamXml
2017-10-23 19:43:08.134INFO 1488 --- [main] c.n.d.s.r.aws.ConfigClusterResolver: Resolving eureka endpoints via configuration
2017-10-23 19:43:08.344INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Disable delta property : false
2017-10-23 19:43:08.344INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Single vip registry refresh property : null
2017-10-23 19:43:08.344INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Force full registry fetch : false
2017-10-23 19:43:08.344INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Application is null : false
2017-10-23 19:43:08.344INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Registered Applications size is zero : true
2017-10-23 19:43:08.344INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Application version is -1: true
2017-10-23 19:43:08.345INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Getting all instance registry info from the eureka server
2017-10-23 19:43:08.630INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: The response status is 200
2017-10-23 19:43:08.631INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Starting heartbeat executor: renew interval is: 30
2017-10-23 19:43:08.634INFO 1488 --- [main] c.n.discovery.InstanceInfoReplicator: InstanceInfoReplicator onDemand update allowed rate per min is 4
2017-10-23 19:43:08.637INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Discovery Client initialized at timestamp 1508758988637 with initial instances count: 0
2017-10-23 19:43:08.657INFO 1488 --- [main] c.n.e.EurekaDiscoveryClientConfiguration : Registering application springms-provider-user with eureka with status UP
2017-10-23 19:43:08.658INFO 1488 --- [main] com.netflix.discovery.DiscoveryClient: Saw local status change event StatusChangeEvent [timestamp=1508758988658, current=UP, previous=STARTING]
2017-10-23 19:43:08.659INFO 1488 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient: DiscoveryClient_SPRINGMS-PROVIDER-USER/springms-provider-user:192.168.3.101:7900: registering service...
2017-10-23 19:43:08.768INFO 1488 --- [main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 7900 (http)
2017-10-23 19:43:08.768INFO 1488 --- [main] c.n.e.EurekaDiscoveryClientConfiguration : Updating port to 7900
2017-10-23 19:43:08.773INFO 1488 --- [main] c.s.cloud.MsProviderUserApplication: Started ProviderApplication in 882.1 seconds (JVM running for 10.398)服务提供方主体加载流程
- 【1】：仔细查看下日志，先是 DefaultLifecycleProcessor 类处理了一些 bean,然后接下来肯定会调用一些实现 SmartLifecycle 类的start 方法；
- 【2】： 接着初始化设置了EurekaClient的状态为 STARTING，初始化编码使用的格式，哪些用JSON，哪些用XML；
- 【3】： 紧接着打印了强制获取注册信息状态为false，已注册的应用大小为0，客户端发送心跳续约，心跳续约间隔为30秒，最后打印Client初始化完成；
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@EnableDiscoveryClient
public @interface EnableEurekaClient {}@EnableEurekaClient
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {}@EnableDiscoveryClient这个注解类有个比较特殊的注解 @Import，由此我们猜想，这里的大多数逻辑是不是都写在这个 EnableDiscoveryClientImportSelector 类呢？
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;
}
}/**
* 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
public static List<
String>
loadFactoryNames(Class<
?>
factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
// 注释：public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
// 注释：这个 jar 包下的一个配置文件
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);
}
}# 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.HostInfoEnvironmentPostProcessorEurekaDiscoveryClientConfiguration
@Configuration
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@ConditionalOnProperty(value = "https://www.songbingjia.com/android/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);
}
}
｝- 首先看到该类实现了SmartLifecycle 接口，那么就肯定会实现 start 方法，而且这个 start 方法感觉应在会被加载执行的。
this.applicationInfoManager.setInstanceStatus(this.instanceConfig.getInitialStatus()) 这段代码有一个观察者模式的回调存在。// ApplicationInfoManager.setInstanceStatus 的方法 public synchronized void setInstanceStatus(InstanceStatus status) {// 打上断点 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); } } } }
- 这个方法会因为状态的改变而回调所有实现 StatusChangeListener 这个类的地方，前提得先注册到 listeners 中去才行。
- 于是乎，我们断定，若想要回调，那么就必须有地方先注册这个事件，而且这个注册还必须提前执行在 start 方法前执行，于是我们得先在ApplicationInfoManager 这个类中找到注册到 listeners 的这个方法。
public void registerStatusChangeListener(StatusChangeListener listener) {// 打上断点
listeners.put(listener.getId(), listener);
}- 于是我们逆向找下 registerStatusChangeListener 被调用的地方。
- 很不巧的是，尽然只有1个地方被调用，这个地方就是 DiscoveryClient.initScheduledTasks 方法，而且 initScheduledTasks
方法又是在 DiscoveryClient 的构造函数里面调用的，同时我们也对 initScheduledTasks 以及 initScheduledTasks 被调用的构造方法地方
打上断点。
- 看着断点依次经过我们上述分析的地方，然后也符合日志打印的顺序，所以我们现在应该是有必要好好看看 DiscoveryClient.initScheduledTasks 这个方法究竟干了什么伟大的事情。然而又想了想，还不如看看 initScheduledTasks 被调用的构造方法。
@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 {
// 注释：定时任务调度准备
scheduler = Executors.newScheduledThreadPool(3,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
// 注释：实例化心跳定时任务线程池
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<
Runnable>
(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
);
// use direct handoff// 注释：实例化缓存刷新定时任务线程池
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<
Runnable>
(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
.setDaemon(true)
.build()
);
// use direct handoffeurekaTransport = 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();
}// 注释：初始化调度任务
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());
}- 从往下看，initScheduledTasks 这个方法顾名思义就是初始化调度任务，所以这里面的内容应该就是重头戏，进入看看。
private void initScheduledTasks() { if (clientConfig.shouldFetchRegistry()) { // registry cache refresh timer // 注释：间隔多久去拉取服务注册信息，默认时间 30秒 int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds(); int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound(); // 注释：定时任务，每间隔 30秒 去拉取一次服务注册信息 scheduler.schedule( new TimedSupervisorTask( "cacheRefresh", scheduler, cacheRefreshExecutor, registryFetchIntervalSeconds, TimeUnit.SECONDS, expBackOffBound, new CacheRefreshThread() ), registryFetchIntervalSeconds, TimeUnit.SECONDS); }if (clientConfig.shouldRegisterWithEureka()) { // 注释：间隔多久发送一次心跳续约，默认间隔时间 30 秒 int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs(); int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound(); logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs); // Heartbeat timer // 注释：定时任务，每间隔 30秒 去想 EurekaServer 发送一次心跳续约 scheduler.schedule( new TimedSupervisorTask( "heartbeat", scheduler, heartbeatExecutor, renewalIntervalInSecs, TimeUnit.SECONDS, expBackOffBound, new HeartbeatThread() ), renewalIntervalInSecs, TimeUnit.SECONDS); // InstanceInfo replicator // 注释：实例信息复制器，定时刷新dataCenterInfo数据中心信息，默认30秒 instanceInfoReplicator = new InstanceInfoReplicator( this, instanceInfo, clientConfig.getInstanceInfoReplicationIntervalSeconds(), 2); // burstSize// 注释：实例化状态变化监听器 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); }// 注释：状态有变化的话，会回调这个方法 instanceInfoReplicator.onDemandUpdate(); } }; // 注释：注册状态变化监听器 if (clientConfig.shouldOnDemandUpdateStatusChange()) { applicationInfoManager.registerStatusChangeListener(statusChangeListener); }instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds()); } else { logger.info("Not registering with Eureka server per configuration"); } }
- 在这个方法从上往下一路注释分析下来，干了EurekaClient我们最想知道的一些事情，定时任务获取注册信息，定时任务刷新缓存，定时任务心跳续约，定时任务同步数据中心数据，状态变化监听回调等。但是唯独没看到注册，这是怎么回事呢？
- instanceInfoReplicator.onDemandUpdate() 就是在状态改变的时候。
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);
}// 注释：这里进行了实例信息刷新和注册
InstanceInfoReplicator.this.run();
}
});
return true;
} else {
logger.warn("Ignoring onDemand update due to rate limiter");
return false;
}
}- onDemandUpdate 这个方法，唯独 InstanceInfoReplicator.this.run() 这个方法还有点用，而且还是 run 方法呢，感情 InstanceInfoReplicator 这个类还是实现了 Runnable 接口？经过查看这个类，还真是实现了 Runnable 接口。
- 这个方法应该我们要找的注册所在的地方。
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);
}
}- 【SpringCloud-技术专区-从源码层面让你认识Eureka工作流程和运作机制（下）】discoveryClient.register() 这个 register 方法，原来注册方法就是这个。
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; }
- 原来调用了 EurekaHttpClient 封装的客户端请求对象来进行注册的，再继续深探 registrationClient.register 方法，于是我们来到了 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)
// 注释：打包带上当前应用的所有信息 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();
}
}
}- 调用的是 Jersey RESTful 框架来进行请求的，然后在 EurekaServer 那边就会在 ApplicationResource.addInstance 方法接收客户端的注册请求，因此我们的 EurekaClient 是如何注册的就到此为止了。
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