Troubleshooting the Kubernetes cluster

In this chapter we will learn about how to trouble shoot our Kubernetes cluster at control plane level and at application level.

Troubleshooting the control plane

Listing the nodes in a cluster

First thing to check if your cluster is working fine or not is to list the nodes associated with your cluster.

kubectl get nodes

Make sure that all nodes are in Ready state.

List the control plane pods

If your nodes are up and running, next thing to check is the status of Kubernetes components. Run,

kubectl get pods -n kube-system

If any of the pod is restarting or crashing, look in to the issue. This can be done by getting the pod's description. For example, in my cluster kube-dns is crashing. In order to fix this first check the deployment for errors.

kubectl describe deployment -n kube-system kube-dns

Log files


If your deployment is good, the next thing to look for is log files. The locations of log files are given below...

/var/log/kube-apiserver.log - For API Server logs
/var/log/kube-scheduler.log - For Scheduler logs
/var/log/kube-controller-manager.log - For Replication Controller logs

If your Kubernetes components are running as pods, then you can get their logs by following the steps given below, Keep in mind that the actual pod's name may differ from cluster to cluster...

kubectl logs -n kube-system -f kube-apiserver-node1
kubectl logs -n kube-system -f kube-scheduler-node1
kubectl logs -n kube-system -f kube-controller-manager-node1

Worker Nodes

In your worker, you will need to check for errors in kubelet's log...

sudo journalctl -u  kubelet

Troubleshooting the application

Sometimes your application(pod) may fail to start because of various reasons. Let's see how to troubleshoot.

Getting detailed status of an object (pods, deployments)

object.status shows a detailed information about whats the status of an object ( e.g. pod) and why its in that condition. This can be very useful to identify the issues.


kubectl get pod vote -o yaml

example output snippet when a wrong image was used to create a pod.

    message: 'rpc error: code = Unknown desc = Error response from daemon: manifest
      for schoolofdevops/vote:latst not found'
    reason: ErrImagePull

Checking the status of Deployment

For this example I have a sample deployment called nginx.

FILE: nginx-deployment.yml

apiVersion: apps/v1beta1
kind: Deployment
  name: nginx
    app: nginx
  replicas: 1
        app: nginx
        - name: nginx
          image: ngnix:latest
            - containerPort: 80

List the deployment to check for the availability of pods

kubectl get deployment nginx

nginx         1         1         1            0           20h

It is clear that my pod is unavailable. Lets dig further.

Check the events of your deployment.

kubectl describe deployment nginx

List the pods to check for any registry related error

kubectl get pods

NAME                           READY     STATUS             RESTARTS   AGE
nginx-57c88d7bb8-c6kpc         0/1       ImagePullBackOff   0          7m

As we can see, we are not able to pull the image(ImagePullBackOff). Let's investigate further.

kubectl describe pod nginx-57c88d7bb8-c6kpc

Check the events of the pod's description.

  Type     Reason                 Age               From                                               Message
  ----     ------                 ----              ----                                               -------
  Normal   Scheduled              9m                default-scheduler                                  Successfully assigned nginx-57c88d7bb8-c6kpc to
  Normal   SuccessfulMountVolume  9m                kubelet,  MountVolume.SetUp succeeded for volume "default-token-8cwn4"
  Normal   Pulling                8m (x4 over 9m)   kubelet,  pulling image "ngnix"
  Warning  Failed                 8m (x4 over 9m)   kubelet,  Failed to pull image "ngnix": rpc error: code = Unknown desc = Error response from daemon: repository ngnix not found: does not exist or no pull access
  Normal   BackOff                7m (x6 over 9m)   kubelet,  Back-off pulling image "ngnix"
  Warning  FailedSync             4m (x24 over 9m)  kubelet,  Error syncing pod

Bingo! The name of the image is ngnix instead of nginx. So fix the typo in your deployment file and redo the deployment.

Sometimes, your application(pod) may fail to start because of some configuration issues. For those errors, we can follow the logs of the pod.

kubectl logs -f nginx-57c88d7bb8-c6kpc

If you have any errors it will get populated in your logs.