背景
公司目前在基于k8s做调度（基于io.fabric8:kubernetes-client:4.2.0），在运行的过程中，遇到了如下问题：
OkHttp WebSocket https://10.25.61.82:6443/...] DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - WebSocket close received. code: 1000, reason: [OkHttp WebSocket https://10.25.61.82:6443/...] DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - Submitting reconnect task to the executor[scheduleReconnect|Executor for Watch 1880052106] DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - Scheduling reconnect task[scheduleReconnect|Executor for Watch 1880052106] DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - Current reconnect backoff is 1000 milliseconds (T0)[reconnectAttempt|Executor for Watch 1880052106] DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - Connecting websocket ... io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager@700f518a199 - 2020-11-17T06:39:13.874Z -[merlion-k8s-backend]-[merlion-k8s-backend-6b4cc44855-s6wnq]: 06:39:13.873 [OkHttp https://10.25.61.82:6443/...] DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - WebSocket successfully opened WARN PodsWatchSnapshotSource: Kubernetes client has been closed (this is expected if the application is shutting down.)io.fabric8.kubernetes.client.KubernetesClientException: too old resource version: 135562761 (135563127)at io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager$1.onMessage(WatchConnectionManager.java:254)[kubernetes-client-4.2.2.jar:?]at okhttp3.internal.ws.RealWebSocket.onReadMessage(RealWebSocket.java:323) [okhttp-3.12.0.jar:?]at okhttp3.internal.ws.WebSocketReader.readMessageFrame(WebSocketReader.java:219) [okhttp-3.12.0.jar:?]at okhttp3.internal.ws.WebSocketReader.processNextFrame(WebSocketReader.java:105) [okhttp-3.12.0.jar:?]at okhttp3.internal.ws.RealWebSocket.loopReader(RealWebSocket.java:274) [okhttp-3.12.0.jar:?]at okhttp3.internal.ws.RealWebSocket$2.onResponse(RealWebSocket.java:214) [okhttp-3.12.0.jar:?]at okhttp3.RealCall$AsyncCall.execute(RealCall.java:206) [okhttp-3.12.0.jar:?]at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32) [okhttp-3.12.0.jar:?]at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_191]at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_191]at java.lang.Thread.run(Thread.java:748) [?:1.8.0_191]单凭这个问题其实没什么，然而代码中是：
watchConnection = kubernetesClient.pods() .withLabel(MERLION_TASK_LABEL, applicationId) // .withResourceVersion(resourceVersion) .watch(new TaskPodsWatcher())因为咱们曾经正文掉了withResourceVersion(resourceVersion),（如果没有正文掉，阐明咱们的代码中设置的resourceVersion太小）然而还会报too old resource version
剖析
间接跳转到WatchConnectionManager onClosed 如下：
@Override public void onClosed(WebSocket webSocket, int code, String reason) { logger.debug("WebSocket close received. code: {}, reason: {}", code, reason); if (forceClosed.get()) { logger.debug("Ignoring onClose for already closed/closing websocket"); return; } if (currentReconnectAttempt.get() >= reconnectLimit && reconnectLimit >= 0) { closeEvent(new KubernetesClientException("Connection unexpectedly closed")); return; } scheduleReconnect(); }对于onclosed的解释是
/** * Invoked when both peers have indicated that no more messages will be transmitted and the * connection has been successfully released. No further calls to this listener will be made. */ public void onClosed(WebSocket webSocket, int code, String reason) { }阐明因为长时间没有event的传输，导致该connect被开释了，从而导致WebSocket 被敞开了（这种在工作不是很多的状况下产生的概率很大），从而进行了重联操作scheduleReconnect，而该办法调用了runWatch():
executor.schedule(new NamedRunnable("reconnectAttempt") { @Override public void execute() { try { runWatch(); reconnectPending.set(false); } catch (Exception e) { // An unexpected error occurred and we didn't even get an onFailure callback. logger.error("Exception in reconnect", e); webSocketRef.set(null); closeEvent(new KubernetesClientException("Unhandled exception in reconnect attempt", e)); close(); } } }, nextReconnectInterval(), TimeUnit.MILLISECONDS); }而在runWatch()办法中，咱们又调用了
if (this.resourceVersion.get() != null) { httpUrlBuilder.addQueryParameter("resourceVersion", this.resourceVersion.get()); }而this.resourceVersion 值的设置在 public void onMessage(WebSocket webSocket, String message) 办法中：
WatchEvent event = readWatchEvent(message); Object object = event.getObject(); if (object instanceof HasMetadata) { @SuppressWarnings("unchecked") T obj = (T) object; // Dirty cast - should always be valid though resourceVersion.set(((HasMetadata) obj).getMetadata().getResourceVersion()); Watcher.Action action = Watcher.Action.valueOf(event.getType()); watcher.eventReceived(action, obj); } else if (object instanceof KubernetesResourceList) { @SuppressWarnings("unchecked") KubernetesResourceList list = (KubernetesResourceList) object; // Dirty cast - should always be valid though resourceVersion.set(list.getMetadata().getResourceVersion()); Watcher.Action action = Watcher.Action.valueOf(event.getType()); List<HasMetadata> items = list.getItems(); if (items != null) { for (HasMetadata item : items) { watcher.eventReceived(action, (T) item); } }也就是说，如果说如果重联的时候间隔上次设置resourceVersion超过了etc保留的最小resourceVersion的话，就会报too old resource version谬误:
解决
通过网上查问kubernetes-too-old-resource-version,该Kubernetes Client team memeber 提到了：
Fabric8 does not handle it with plain watch. But it is handling it in SharedInformer API, see ReflectorWatcher. I would recommend using informer API when writing operators since it's better than plain list and watch也就是说,咱们能够用SharedInformer api来实现，而watch机制解决不了这种状况，所以咱们能够用SharedInformer实现，截止到2020年11月16日，咱们获取到kubernetes-client最新版本，kubernetes-client:4.13.0,编码实现:
val sharedInformerFactory = kubernetesClient.informers() val podInformer = sharedInformerFactory .sharedIndexInformerFor(classOf[Pod], classOf[PodList], new OperationContext().withNamespace("test"), 30 * 1000L) podInformer.addEventHandler(new ResourceEventHandler[Pod] { override def onAdd(obj: Pod): Unit = { eventReceived(obj, "ADD") } override def onDelete(obj: Pod, deletedFinalStateUnknown: Boolean): Unit = { eventReceived(obj, "DELETE") } override def onUpdate(oldObj: Pod, newObj: Pod): Unit = { eventReceived(newObj, "UPDATE") } private def idShouldUpdate(pod: Pod): Boolean = { pod.getMetadata.getLabels.getOrDefault(MERLION_TASK_LABEL, "") == applicationId } private def eventReceived(pod: Pod, action: String): Unit = { if (idShouldUpdate(pod)) { val podName = pod.getMetadata.getName logger.info(s"Received job pod update for pod named $podName, action ${action}") snapshotsStore.updatePod(pod) } } }) sharedInformerFactory.startAllRegisteredInformers() }其中SharedInformerFactory的机制和k8s Informer机制一样的，可能保障音讯的可靠性,
其中最次要的是ReflectorWatcher和Reflector和DefaultSharedIndexInformer,咱们简略的剖析一下：
public DefaultSharedIndexInformer(Class<T> apiTypeClass, ListerWatcher<T, L> listerWatcher, long resyncPeriod, OperationContext context, ConcurrentLinkedQueue<SharedInformerEventListener> eventListeners) { this.resyncCheckPeriodMillis = resyncPeriod; this.defaultEventHandlerResyncPeriod = resyncPeriod; this.processor = new SharedProcessor<>(); this.indexer = new Cache(); DeltaFIFO<T> fifo = new DeltaFIFO<>(Cache::metaNamespaceKeyFunc, this.indexer); this.controller = new Controller<>(apiTypeClass, fifo, listerWatcher, this::handleDeltas, processor::shouldResync, resyncCheckPeriodMillis, context, eventListeners); controllerThread = new Thread(controller::run, "informer-controller-" + apiTypeClass.getSimpleName()); }DefaultSharedIndexInformer 中，用DeltaFIFO作为event的存储，而this::handleDeltas的调用是在Controller作为this.queue.pop 的参数processFunc函数被调用，也就是说这个函数来生产fifo外面的event,如下：
private void processLoop() throws Exception { while (true) { try { this.queue.pop(this.processFunc); } catch (InterruptedException t) { log.error("DefaultController#processLoop got interrupted {}", t.getMessage(), t); return; } catch (Exception e) { log.error("DefaultController#processLoop recovered from crashing {} ", e.getMessage(), e); throw e; } } 而queue也是DeltaFIFO的形参传进来的，也就是说queue就是fifo，而fifo外面的数据从哪里来呢？在controller::run函数中:
if (fullResyncPeriod > 0) { reflector = new Reflector<>(apiTypeClass, listerWatcher, queue, operationContext, fullResyncPeriod); } else { reflector = new Reflector<>(apiTypeClass, listerWatcher, queue, operationContext, DEFAULT_PERIOD); }reflector.listAndWatch()将会调用reflector.listAndWatch()办法，该办法进行相似k8s的list-watch机制，如下：
public void listAndWatch() throws Exception { try { log.info("Started ReflectorRunnable watch for {}", apiTypeClass); reListAndSync(); resyncExecutor.scheduleWithFixedDelay(this::reListAndSync, 0L, resyncPeriodMillis, TimeUnit.MILLISECONDS); startWatcher(); } catch (Exception exception) { store.isPopulated(false); throw new RejectedExecutionException("Error while starting ReflectorRunnable watch", exception); } }reListAndSync进行全量event数据的拉取，startWatcher进行watch，获取增量event数据，那这个watch是什么呢？如下：
watch.set( listerWatcher.watch(new ListOptionsBuilder() .withWatch(Boolean.TRUE).withResourceVersion(lastSyncResourceVersion.get()).withTimeoutSeconds(null).build(), operationContext.getNamespace(), operationContext, watcher) )这里的watcher在reflector的构造函数中初始化
watcher = new ReflectorWatcher<>(store, lastSyncResourceVersion, this::startWatcher, this::reListAndSync);而ReflectorWatcher是继承自Watcher，所以也有对应的eventReceived办法和onClose办法，如下:
@Override public void eventReceived(Action action, T resource) { if (action == null) { final String errorMessage = String.format("Unrecognized event %s", resource.getMetadata().getName()); log.error(errorMessage); throw new KubernetesClientException(errorMessage); } log.info("Event received {}", action.name()); switch (action) { case ERROR: final String errorMessage = String.format("ERROR event for %s", resource.getMetadata().getName()); log.error(errorMessage); throw new KubernetesClientException(errorMessage); case ADDED: store.add(resource); break; case MODIFIED: store.update(resource); break; case DELETED: store.delete(resource); break; } lastSyncResourceVersion.set(resource.getMetadata().getResourceVersion()); log.debug("{}#Receiving resourceVersion {}", resource.getKind(), lastSyncResourceVersion.get()); } @Override public void onClose(KubernetesClientException exception) { log.error("Watch closing"); Optional.ofNullable(exception) .map(e -> { log.debug("Exception received during watch", e); return exception; }) .map(KubernetesClientException::getStatus) .map(Status::getCode) .filter(c -> c.equals(HttpURLConnection.HTTP_GONE)) .ifPresent(c -> onHttpGone.run()); onClose.run(); }在eventReceived办法中，所有音讯的都会增加到store中也就是fifo的queue中,在onClose办法中，咱们看到如果HTTP_GONE，也就是too old resource version的话，会进行onHttpGone.run(),也会进行onClose.run(）,而
onHttpGone就是Reflector的reListAndSync函数，onClose是Reflector的startWatcher函数,也就是说一旦该watcher被敞开，就会从新进行watch。
留神
在kubernetes-client:4.6.2中,WatchConnectionManager onMessage 对于HTTP_GONE的解决是不一样的,如下：
if (status.getCode() == HTTP_GONE) { logger.info("The resource version {} no longer exists. Scheduling a reconnect.", resourceVersion.get()); resourceVersion.set(null); scheduleReconnect(); } else { logger.error("Error received: {}", status.toString()); }一旦产生了HTTP_GONE,,会把resourceVersion设置为null,也就是获取最新的event，而且会立刻重联，而在4.13.0版本和4.2.0版本，是不会立刻重联，而是让用户去解决的。