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Troubleshooting And Debugging Kubernetes

Troubleshooting K8s - Common Issues in K8S - finding the reasons and Fixing Them#

Pod in ImagePullBackOff#

With an error message like: Back-off pulling image

A lot of tutorials say uou should use describe on the pod. This is wrong. You cannot describe the pod if it is not running. It will not be running as k8s cannot even get the image is should run.

The best place to start is to look at the events of a pod with:

kubectl get event -n portal --field-selector

You will get output like:

LAST SEEN   TYPE      REASON    OBJECT                                 MESSAGE
21m         Normal    BackOff   pod/my-pod-zl6m6   Back-off pulling image ""
71s         Warning   Failed    pod/my-pod-zl6m6   Error: ImagePullBackOff

but that is telling us what we already know.

If there is only 1 pod in the namespace it is easier to look at all events in the namespace:

kubectl get event -n portal

But there is no clear indication except for in rancher on a rare occasion it will show the actual error from the registry:

ErrImagePull: rpc error: code = Unknown desc = Error response from daemon: Get Get https://core.harbor.domain/service/token?scope=repository%3Acrepo%2Fimage_name%3Apull&service=harbor-registry: dial tcp: lookup core.harbor.domain: no such host

In which case sometimes the registry gives errors…

A Pod is stuck in Pending State#

Here a MySQL pod has been stuck for 48 minutes in a Pending state

$ kubectl get pods
mysql-6q5hp   0/1     Pending   0          48m

Describe the pod:

$ kubectl describe pod mysql-6q5hp
Name:           mysql-6q5hp
Namespace:      default
Priority:       0
Node:           <none>
Labels:         app=mysql
Annotations:    <none>
Status:         Pending
IPs:            <none>
Controlled By:  ReplicaSet/mysql
    Image:      mysql
    Port:       3306/TCP
    Host Port:  0/TCP
    cpu:     1
    memory:  2Gi
    Liveness:  tcp-socket :3306 delay=0s timeout=1s period=10s #success=1 #failure=3
    MYSQL_ROOT_PASSWORD:  some-password-here
    /var/lib/mysql from database (rw)
    /var/run/secrets/ from default-token-mbn5b (ro)
Type           Status
PodScheduled   False 
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  database
    ReadOnly:   false
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-mbn5b
    Optional:    false
QoS Class:       Burstable
Node-Selectors:  <none>
Tolerations: for 300s
       for 300s
Type     Reason            Age        From               Message
----     ------            ----       ----               -------
Warning  FailedScheduling  <unknown>  default-scheduler  0/1 nodes are available: 1 Insufficient memory.
Warning  FailedScheduling  <unknown>  default-scheduler  0/1 nodes are available: 1 Insufficient memory.

Source: My pod stays pending

Pod Status shows a RunContainerError#

$ kubectl get pods -w
NAME                       READY   STATUS              RESTARTS   AGE
nginx-fast-storage-wknfz   1/1     Running             0          128m
parallel-kcvxt             0/1     ContainerCreating   0          10s
parallel-lpttv             0/1     ContainerCreating   0          10s
parallel-ng5xd             0/1     RunContainerError   0          10s
parallel-pjwdz             0/1     ContainerCreating   0          10s
parallel-vnskl             0/1     ContainerCreating   0          10s
parallel-pjwdz             0/1     RunContainerError   0          11s
parallel-lpttv             0/1     RunContainerError   0          13s
parallel-vnskl             0/1     RunContainerError   0          16s
parallel-kcvxt             0/1     RunContainerError   0          19s

Check the events for any info

You can get the events causing the error:

kubectl get events --sort-by=.metadata.creationTimestamp

That said the error:

41m         Normal    Created                pod/parallel-ng5xd   Created container kuard
41m         Warning   Failed                 pod/parallel-ng5xd   Error: failed to start container "kuard": Error response from daemon: OCI runtime create failed: container_linux.go:345: starting container process caused "exec: \"--keygen-enable\": executable file not found in $PATH": unknown

View DNS Records#

kubectl get pods -n kube-system

Pod in CrashLoopBackoff shows secrets error in logs#

Check pod status

$ kubectl get po
NAME                                                   READY   STATUS             RESTARTS   AGE
dashboard-demo-kubernetes-dashboard-59db4d65dc-dnbx8   0/1     CrashLoopBackOff   6          8m11s

Check the logs:

kubectl logs dashboard-demo-kubernetes-dashboard-59db4d65dc-dnbx8
Storing encryption key in a secret
panic: secrets is forbidden: User "system:serviceaccount:default:dashboard-demo-kubernetes-dashboard" cannot create resource "secrets" in API group "" in the namespace "kube-system"