The commands/steps listed on this page can be used to check networking related issues in your cluster.

Make sure you configured the correct kubeconfig (for example, export KUBECONFIG=$PWD/kube_config_rancher-cluster.yml for Rancher HA) or are using the embedded kubectl via the UI.

Double check if all the required ports are opened in your (host) firewall

Double check if all the required ports are opened in your (host) firewall. The overlay network uses UDP in comparison to all other required ports which are TCP.

Check if overlay network is functioning correctly

The pod can be scheduled to any of the hosts you used for your cluster, but that means that the NGINX ingress controller needs to be able to route the request from NODE_1 to NODE_2. This happens over the overlay network. If the overlay network is not functioning, you will experience intermittent TCP/HTTP connection failures due to the NGINX ingress controller not being able to route to the pod.

To test the overlay network, you can launch the following DaemonSet definition. This will run an alpine container on every host, which we will use to run a ping test between containers on all hosts.

  1. Save the following file as ds-overlaytest.yml

    apiVersion: apps/v1
    kind: DaemonSet
    metadata:
      name: overlaytest
    spec:
      selector:
          matchLabels:
            name: overlaytest
      template:
        metadata:
          labels:
            name: overlaytest
        spec:
          tolerations:
          - operator: Exists
          containers:
          - image: busybox:1.28
            imagePullPolicy: Always
            name: alpine
            command: ["sh", "-c", "tail -f /dev/null"]
            terminationMessagePath: /dev/termination-log
    
  2. Launch it using kubectl create -f ds-overlaytest.yml

  3. Wait until kubectl rollout status ds/overlaytest -w returns: daemon set "overlaytest" successfully rolled out.

  4. Run the following command, from the same location, to let each container on every host ping each other (it’s a single line bash command).

    echo "=> Start network overlay test"; kubectl get pods -l name=overlaytest -o jsonpath='{range .items[*]}{@.metadata.name}{" "}{@.spec.nodeName}{"\n"}{end}' | while read spod shost; do kubectl get pods -l name=overlaytest -o jsonpath='{range .items[*]}{@.status.podIP}{" "}{@.spec.nodeName}{"\n"}{end}' | while read tip thost; do kubectl --request-timeout='10s' exec $spod -- /bin/sh -c "ping -c2 $tip > /dev/null 2>&1"; RC=$?; if [ $RC -ne 0 ]; then echo $shost cannot reach $thost; fi; done; done; echo "=> End network overlay test"
    
  5. When this command has finished running, the output indicating everything is correct is:

    => Start network overlay test
    => End network overlay test
    

If you see error in the output, that means that the required ports for overlay networking are not opened between the hosts indicated.

Example error output of a situation where NODE1 had the UDP ports blocked.

=> Start network overlay test
command terminated with exit code 1
NODE2 cannot reach NODE1
command terminated with exit code 1
NODE3 cannot reach NODE1
command terminated with exit code 1
NODE1 cannot reach NODE2
command terminated with exit code 1
NODE1 cannot reach NODE3
=> End network overlay test

Cleanup the alpine DaemonSet by running kubectl delete ds/overlaytest.

Check if MTU is correctly configured on hosts and on peering/tunnel appliances/devices

When the MTU is incorrectly configured (either on hosts running Rancher, nodes in created/imported clusters or on appliances/devices in between), error messages will be logged in Rancher and in the agents, similar to:

  • websocket: bad handshake
  • Failed to connect to proxy
  • read tcp: i/o timeout

See Google Cloud VPN: MTU Considerations for an example how to configure MTU correctly when using Google Cloud VPN between Rancher and cluster nodes.

Resolved issues

Overlay network broken when using Canal/Flannel due to missing node annotations

GitHub issue #13644
Resolved in v2.1.2

To check if your cluster is affected, the following command will list nodes that are broken (this command requires jq to be installed):

kubectl get nodes -o json | jq '.items[].metadata | select(.annotations["flannel.alpha.coreos.com/public-ip"] == null or .annotations["flannel.alpha.coreos.com/kube-subnet-manager"] == null or .annotations["flannel.alpha.coreos.com/backend-type"] == null or .annotations["flannel.alpha.coreos.com/backend-data"] == null) | .name'

If there is no output, the cluster is not affected.

System namespace pods network connectivity broken

Note: This applies only to Rancher upgrades from v2.0.6 or earlier to v2.0.7 or later. Upgrades from v2.0.7 to later version are unaffected.

GitHub issue #15146

If pods in system namespaces cannot communicate with pods in other system namespaces, you will need to follow the instructions in Upgrading to v2.0.7+ — Namespace Migration to restore connectivity. Symptoms include:

  • NGINX ingress controller showing 504 Gateway Time-out when accessed.
  • NGINX ingress controller logging upstream timed out (110: Connection timed out) while connecting to upstream when accessed.