【k8s系列5】KubernetesClientException: too old resource version 原因分析

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：

DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - WebSocket close received. code: 1000, reason:
 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@700f518a
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，但是代码中是：

  watchConnection = kubernetesClient.pods()
         .withLabel(MERLION_TASK_LABEL, applicationId)
         //      .withResourceVersion(resourceVersion)
         .watch(new TaskPodsWatcher())

因为我们已经注释掉了withResourceVersion(resourceVersion),（如果没有注释掉，说明我们的代码中设置的resourceVersion太小）但是还会报too old resource version

分析

直接跳转到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) {
  }

说明由于长时间没有event的传输，导致该connect被释放了，从而导致WebSocket 被关闭了（这种在任务不是很多的情况下发生的概率很大），从而进行了重联操作scheduleReconnect，而该方法调用了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()方法中，我们又调用了

 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) 方法中：

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，假如说如果重联的时候距离上次设置resourceVersion超过了etc保留的最小resourceVersion的话，就会报too old resource version错误:

解决

通过网上查询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,我们可以用SharedInformer api来实现，而watch机制处理不了这种情况，所以我们可以用SharedInformer实现，截止到2020年11月16日，我们获取到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，能够保证消息的可靠性,
其中最主要的是ReflectorWatcher和Reflector和DefaultSharedIndexInformer,我们简单的分析一下：

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消费fifo里面的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里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()方法，该方法进行类似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方法和onClose方法，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方法中，所有消息的都会添加到store中也就是fifo的queue中,在onClose方法中，我们看到如果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被关闭，就会重新进行watch。

注意

在kubernetes-client:4.6.2中,WatchConnectionManager onMessage 对于HTTP_GONE的处理是不一样的,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());
              }

一旦发生了HTTP_GONE,,会把resourceVersion设置为null,也就是获取最新的event，而且会立即重联，而在4.13.0版本和4.2.0版本，是不会立即重联，而是让用户去处理的。