Change:
//    be less than the node health signal update frequency, since there will //    only be fresh values from Kubelet at an interval of node health signal //    update frequency. <del> // 2. nodeMonitorGracePeriod can't be too large for user experience - larger </del> <ins> // 2. nodeMonitorGracePeriod should be greater than the sum of HTTP2_PING_TIMEOUT_SECONDS (30s) // 	  and HTTP2_READ_IDLE_TIMEOUT_SECONDS (15s) from the http2 health check // 	  to ensure that the server has adequate time to handle slow or idle connections //    properly before marking a node as unhealthy. // 3. nodeMonitorGracePeriod can't be too large for user experience - larger </ins> //    value takes longer for user to see up-to-date node health. nodeMonitorGracePeriod time.Duration

Discussion:
The controller-manager node-lifecycle-controller watches node lease and update probeTimestamp , and it check node probeTimestamp is before . The node-monitor-grace-period default value is 40s. When the client connection lost, the lease watcher cannot receive new event. With the http2 health check, HTTP2PINGTIMEOUTSECONDS default is 30s, HTTP2READIDLETIMEOUTSECONDS default is 15s, it will delay 45s to kill http2 connection. During this period, node-lifecycle-controller will mark all nodes NotReady. Here are some logs When the http2 connection lost, the watch should stop as soon as possible. The reflector should relist resource, and node-lifecycle-controller should not mark all node NotReady. HTTP2PINGTIMEOUTSECONDS+HTTP2READIDLETIMEOUTSECONDS should be less than 40s. the controller-manager node-lifecycle-controller watch client srcIP:srcPort. Drop all tcp package send into srcIP:srcPort. for more than 40 seconds, all node will be marked NotReady node will be Ready after some seconds. No response <details</details<details</details<details</details<details</details<details</details<details</details
How about double-check node lease before marking node NotReady? The node-lifecycle-controller can get reference lease from apiserver with
/sig node
/sig api-machinery
/cc We have discussed this timeouts values before and myself, I also think got some metrics with lower timeouts for the HTTP2 connections. In this situation is clear that the defaults of the node watcher and the timeouts are related and having good defaults will be ideal, but the question is which values do we change ?
I think in internal network, the ping response almost return in 1 second, the HTTP2PINGTIMEOUT_SECONDS default value should be 5 seconds. And the total timeout will 35 seconds. WDYT?
/triage accepted any pointers in other places where those timeouts were changed for http2? Any notes from those discussions?
/priority important-longterm since it is not a regression I will keep it longterm priority and not higher. But we can reevaluate if we hear more reports about it.

/assign
I'm investigating problems similar to this, but I'm looking for a way to confirm this is what is happening - and if there are tips for how to recreate such a scenario, that would be very helpful. We get infrequent reports of "worker goes NotReady for a short time" incidents that appear to be triggered by events like failing over a LB sitting front of the kube-apiservers. We've done some tests with a simple client-go app and have recreated a scenario in which the app logs messages after 45 secs of "context exceeded" errors. The failures reported to us from customers don't have http2 errors in the kubelet logs, and our attempts to recreate with kubelet have never shown more more than a single error which works on subsequent retry.
Hi folks, we have a simulated recreate of the problem. This recreate involves injecting a 40 second delay in "connectivity" between the Kubernetes API server and etcd (we a 40 second delay to etcd defrag and defragged all etcd members at the same time). The connectivity between these two components is obviously critical to nodes successfully updating their leases in order to stay ready. We use 40 seconds because it matches . The test will usually cause one or more of the cluster nodes will flap their readiness state. Setting on the Kubernetes controller manager prevents the flap. Given this, I think that one or more of the Kubernetes default configurations needs to change in order to tolerate such "connectivity" problems in order to maintain healthy node state.
What's the proposal then? Do we update --node-monitor-grace-period to 50s? It seems the less risky change as the client-go defaults are more sensitive and impact the whole ecosystem, beyond kubernetes itself are you open to increase this default? It seems worth it to improve the reliability of cluster
I think we should update .
can someone send a PR to see how it will look like?
I have been following this discussion as we had encountered the bug as well. I have created a PR - Please let me know if it works
I'll add another data point from our testing. Namely, the simulated recreate noted depends on the Kubernetes controller manager (KCM) leader election configuration. Using the following leader election configuration for the KCM yields a KCM that has no leader after the delayed etcd defrag.

As a result, nodes won't be marked not ready unless the KCM leadership is restored before the nodes renew their lease. Extending the KCM leader election configuration to the following, makes the problem easier to recreate.
/assign Reassigning the issue to me