Code change:
<ins> /* Copyright 2020 The Kubernetes Authors. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. */ package network import ( "fmt" "strings" "time" "github.com/onsi/ginkgo" v1 "k8s.io/api/core/v1" metav1 "k8s.io/apimachinery/pkg/apis/meta/v1" "k8s.io/apimachinery/pkg/util/intstr" clientset "k8s.io/client-go/kubernetes" "k8s.io/kubernetes/test/e2e/framework" e2enode "k8s.io/kubernetes/test/e2e/framework/node" e2epod "k8s.io/kubernetes/test/e2e/framework/pod" e2eservice "k8s.io/kubernetes/test/e2e/framework/service" e2eskipper "k8s.io/kubernetes/test/e2e/framework/skipper" ) const ( serviceName = "svc-udp" podClient   = "pod-client" podBackend1 = "pod-server-1" podBackend2 = "pod-server-2" srcPort     = 12345 ) // Linux NAT uses conntrack to perform NAT, everytime a new // flow is seen, a connection is created in the conntrack table, and it // is being used by the NAT module. // Each entry in the conntrack table has associated a timeout, that removes // the connection once it expires. // UDP is a connectionless protocol, so the conntrack module tracking functions // are not very advanced. // It uses a short timeout (30 sec by default) that is renewed if there are new flows // matching the connection. Otherwise it expires the entry. // This behaviour can cause issues in Kubernetes when one entry on the conntrack table // is never expired because the sender does not stop sending traffic, but the pods or // endpoints were deleted, blackholing the traffic // In order to mitigate this problem, Kubernetes delete the stale entries: // - when an endpoint is removed // - when a service goes from no endpoints to new endpoint // Ref: https://api.semanticscholar.org/CorpusID:198903401 // Boye, Magnus. “Netfilter Connection Tracking and NAT Implementation.” (2012). var _ = SIGDescribe("Conntrack", func() { fr := framework.NewDefaultFramework("conntrack") type nodeInfo struct { name   string nodeIP string } var ( cs                             clientset.Interface ns                             string clientNodeInfo, serverNodeInfo nodeInfo ) ginkgo.BeforeEach(func() { cs = fr.ClientSet ns = fr.Namespace.Name nodes, err := e2enode.GetBoundedReadySchedulableNodes(cs, 2) framework.ExpectNoError(err) if len(nodes.Items) < 2 { e2eskipper.Skipf( "Test requires >= 2 Ready nodes, but there are only %v nodes", len(nodes.Items)) } ips := e2enode.CollectAddresses(nodes, v1.NodeInternalIP) clientNodeInfo = nodeInfo{ name:   nodes.Items[0].Name, nodeIP: ips[0], } serverNodeInfo = nodeInfo{ name:   nodes.Items[1].Name, nodeIP: ips[1], } }) ginkgo.It("should be able to preserve UDP traffic when server pod cycles for a NodePort service", func() { // Create a NodePort service udpJig := e2eservice.NewTestJig(cs, ns, serviceName) ginkgo.By("creating a UDP service " + serviceName + " with type=NodePort in " + ns) udpService, err := udpJig.CreateUDPService(func(svc *v1.Service) { svc.Spec.Type = v1.ServiceTypeNodePort svc.Spec.Ports = []v1.ServicePort{ {Port: 80, Name: "udp", Protocol: v1.ProtocolUDP, TargetPort: intstr.FromInt(80)}, } }) framework.ExpectNoError(err) // Create a pod in one node to create the UDP traffic against the NodePort service every 5 seconds ginkgo.By("creating a client pod for probing the service " + serviceName) clientPod := newAgnhostPod(podClient, "") clientPod.Spec.NodeName = clientNodeInfo.name cmd := fmt.Sprintf(`date; for i in $(seq 1 300); do echo "$(date) Try: ${i}"; echo hostname | nc -u -w 5 -p %d %s %d; echo; done`, srcPort, serverNodeInfo.nodeIP, udpService.Spec.Ports[0].NodePort) clientPod.Spec.Containers[0].Command = []string{"/bin/sh", "-c", cmd} clientPod.Spec.Containers[0].Name = podClient fr.PodClient().CreateSync(clientPod) // Read the client pod logs logs, err := e2epod.GetPodLogs(cs, ns, podClient, podClient) framework.ExpectNoError(err) framework.Logf("Pod client logs: %s", logs) // Add a backend pod to the service in the other node ginkgo.By("creating a backend pod " + podBackend1 + " for the service " + serviceName) serverPod1 := newAgnhostPod(podBackend1, "netexec", fmt.Sprintf("--udp-port=%d", 80)) serverPod1.Labels = udpJig.Labels serverPod1.Spec.NodeName = serverNodeInfo.name fr.PodClient().CreateSync(serverPod1) // Waiting for service to expose endpoint. err = validateEndpointsPorts(cs, ns, serviceName, portsByPodName{podBackend1: {80}}) framework.ExpectNoError(err, "failed to validate endpoints for service %s in namespace: %s", serviceName, ns) // Check that the pod receives the traffic // UDP conntrack entries timeout is 30 sec by default ginkgo.By("checking client pod connected to the backend 1 on Node IP " + serverNodeInfo.nodeIP) time.Sleep(30 * time.Second) logs, err = e2epod.GetPodLogs(cs, ns, podClient, podClient) framework.ExpectNoError(err) framework.Logf("Pod client logs: %s", logs) if !strings.Contains(string(logs), podBackend1) { framework.Failf("Failed to connecto to backend 1") } // Create a second pod ginkgo.By("creating a second backend pod " + podBackend2 + " for the service " + serviceName) serverPod2 := newAgnhostPod(podBackend2, "netexec", fmt.Sprintf("--udp-port=%d", 80)) serverPod2.Labels = udpJig.Labels serverPod2.Spec.NodeName = serverNodeInfo.name fr.PodClient().CreateSync(serverPod2) // and delete the first pod framework.Logf("Cleaning up %s pod", podBackend1) fr.PodClient().DeleteSync(podBackend1, metav1.DeleteOptions{}, framework.DefaultPodDeletionTimeout) // Check that the second pod keeps receiving traffic // UDP conntrack entries timeout is 30 sec by default ginkgo.By("checking client pod connected to the backend 2 on Node IP " + serverNodeInfo.nodeIP) time.Sleep(30 * time.Second) logs, err = e2epod.GetPodLogs(cs, ns, podClient, podClient) framework.ExpectNoError(err) framework.Logf("Pod client logs: %s", logs) if !strings.Contains(string(logs), podBackend2) { framework.Failf("Failed to connecto to backend 2") } }) ginkgo.It("should be able to preserve UDP traffic when server pod cycles for a ClusterIP service", func() { // Create a NodePort service udpJig := e2eservice.NewTestJig(cs, ns, serviceName) ginkgo.By("creating a UDP service " + serviceName + " with type=ClusterIP in " + ns) udpService, err := udpJig.CreateUDPService(func(svc *v1.Service) { svc.Spec.Type = v1.ServiceTypeClusterIP svc.Spec.Ports = []v1.ServicePort{ {Port: 80, Name: "udp", Protocol: v1.ProtocolUDP, TargetPort: intstr.FromInt(80)}, } }) framework.ExpectNoError(err) // Create a pod in one node to create the UDP traffic against the NodePort service every 5 seconds ginkgo.By("creating a client pod for probing the service " + serviceName) clientPod := newAgnhostPod(podClient, "") clientPod.Spec.NodeName = clientNodeInfo.name cmd := fmt.Sprintf(`date; for i in $(seq 1 300); do echo "$(date) Try: ${i}"; echo hostname | nc -u -w 5 -p %d %s %d; echo; done`, srcPort, udpService.Spec.ClusterIP, udpService.Spec.Ports[0].Port) clientPod.Spec.Containers[0].Command = []string{"/bin/sh", "-c", cmd} clientPod.Spec.Containers[0].Name = podClient fr.PodClient().CreateSync(clientPod) // Read the client pod logs logs, err := e2epod.GetPodLogs(cs, ns, podClient, podClient) framework.ExpectNoError(err) framework.Logf("Pod client logs: %s", logs) // Add a backend pod to the service in the other node ginkgo.By("creating a backend pod " + podBackend1 + " for the service " + serviceName) serverPod1 := newAgnhostPod(podBackend1, "netexec", fmt.Sprintf("--udp-port=%d", 80)) serverPod1.Labels = udpJig.Labels serverPod1.Spec.NodeName = serverNodeInfo.name fr.PodClient().CreateSync(serverPod1) // Waiting for service to expose endpoint. err = validateEndpointsPorts(cs, ns, serviceName, portsByPodName{podBackend1: {80}}) framework.ExpectNoError(err, "failed to validate endpoints for service %s in namespace: %s", serviceName, ns) // Check that the pod receives the traffic // UDP conntrack entries timeout is 30 sec by default ginkgo.By("checking client pod connected to the backend 1 on Node IP " + serverNodeInfo.nodeIP) time.Sleep(30 * time.Second) logs, err = e2epod.GetPodLogs(cs, ns, podClient, podClient) framework.ExpectNoError(err) framework.Logf("Pod client logs: %s", logs) if !strings.Contains(string(logs), podBackend1) { framework.Failf("Failed to connecto to backend 1") } // Create a second pod ginkgo.By("creating a second backend pod " + podBackend2 + " for the service " + serviceName) serverPod2 := newAgnhostPod(podBackend2, "netexec", fmt.Sprintf("--udp-port=%d", 80)) serverPod2.Labels = udpJig.Labels serverPod2.Spec.NodeName = serverNodeInfo.name fr.PodClient().CreateSync(serverPod2) // and delete the first pod framework.Logf("Cleaning up %s pod", podBackend1) fr.PodClient().DeleteSync(podBackend1, metav1.DeleteOptions{}, framework.DefaultPodDeletionTimeout) // Check that the second pod keeps receiving traffic // UDP conntrack entries timeout is 30 sec by default ginkgo.By("checking client pod connected to the backend 2 on Node IP " + serverNodeInfo.nodeIP) time.Sleep(30 * time.Second) logs, err = e2epod.GetPodLogs(cs, ns, podClient, podClient) framework.ExpectNoError(err) framework.Logf("Pod client logs: %s", logs) if !strings.Contains(string(logs), podBackend2) { framework.Failf("Failed to connecto to backend 2") } }) }) </ins>

Related discussion:
text: Maybe we can increase the timeout and/or switch to a TCP based test:
the test should use UDP, and UDP is unreliable by definition ... however is curious that most of the failures happen because it is not able to communicate with the first pod I think that is something that should be investigated, I've analyzed some occurences and it works fine for the second pod, however, the UDP losses should be totally random
Hi everyone, yeah so.. collecting some data on this... using a two node kind cluster, locally, with the antrea plugin, it passes using a 4 node AWS cluster with the antrea CNI plugin, it failed using a two node kidn cluster locally with calico, it passes So I guess the best reproducer is to run these tests, for now, in the cloud.... Now that I have a reproducer for this maybe can live debug it some time next wk with one of yall :)
bear in mind that this test is connecting to a nodePort in the node IP, the test is functionally correct, it may be flaky due to the unreliable UDP nature or due to the pod scheduling, but if is failing constantly it has to be environmental.
Second failure after two weeks of green 5k runs:
yep, :/ https://k8s-|UDP /assign
/reopen I'm afraid this is going to be challenging :smile: The difference now is that we are testing NodePort and ClusterIP If both fail, we can blame the test for sure, If only NodePort fails, we need to check the job, if GCE or KIND If only ClusterIP fails, ... :thinking:
Reopened this issue. <detailsIn response to : /reopen I'm afraid this is going to be challenging :smile: Instructions for interacting with me using PR comments are available . If you have questions or suggestions related to my behavior, please file an issue against the repository. </details
We're hitting this really frequently in 5k-node tests. So I started looking a little bit into that.