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
[reconnectAttempt|Executor for Watch 1880052106] DEBUG io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager - Connecting websocket ... io.fabric8.kubernetes.client.dsl.internal.WatchConnectionManager@700f518a
199 - 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，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。
来源：oschina
链接：https://my.oschina.net/monkeyboy/blog/4722216