Kubernetes Troubleshooting – The Complete Guide

What is Kubernetes Troubleshooting?

Kubernetes troubleshooting is the process of identifying, diagnosing, and resolving issues in Kubernetes clusters, nodes, pods, or containers.

More broadly defined, Kubernetes troubleshooting also includes effective ongoing management of faults and taking measures to prevent issues in Kubernetes components.

Kubernetes troubleshooting can be very complex. This article will focus on:

• Providing solutions to common errors, including CreateContainerConfigError, ImagePullBackOff, CrashLoopBackOff and Kubernetes Node Not Ready.
• Explaining initial diagnosis of problems in Kubernetes pods and clusters.
• Showing where to find logs and other information required for deeper analysis.

This is part of an extensive series of guides about Kubernetes.

The Three Pillars of Kubernetes Troubleshooting

Tips from the expert

Itiel Shwartz

Co-Founder & CTO

Itiel is the CTO and co-founder of Komodor. He’s a big believer in dev empowerment and moving fast, has worked at eBay, Forter and Rookout (as the founding engineer). Itiel is a backend and infra developer turned “DevOps”, an avid public speaker that loves talking about things such as cloud infrastructure, Kubernetes, Python, observability, and R&D culture.

In my experience, here are tips that can help you better troubleshoot Kubernetes:

Use namespaces for isolation

Organize your clusters by namespaces to isolate different environments (e.g., dev, staging, prod) for more targeted troubleshooting.

Enable audit logging

Turn on Kubernetes audit logging to capture detailed events for security and debugging purposes.

Utilize resource quotas

Set resource quotas to prevent a single application from exhausting cluster resources, which can lead to easier identification of resource contention issues.

Automate node health checks

Implement automated health checks and alerts for node conditions such as disk pressure, memory pressure, and network availability.

Employ Kubernetes Operators

Use operators to automate complex application lifecycles and maintain stateful applications more reliably.

Why is Kubernetes Troubleshooting so Difficult?

Kubernetes is a complex system, and troubleshooting issues that occur somewhere in a Kubernetes cluster is just as complicated.

Even in a small, local Kubernetes cluster, it can be difficult to diagnose and resolve issues, because an issue can represent a problem in an individual container, in one or more pods, in a controller, a control plane component, or more than one of these.

In a large-scale production environment, these issues are exacerbated, due to the low level of visibility and a large number of moving parts. Teams must use multiple tools to gather the data required for troubleshooting and may have to use additional tools to diagnose issues they detect and resolve them.

To make matters worse, Kubernetes is often used to build microservices applications, in which each microservice is developed by a separate team. In other cases, there are DevOps and application development teams collaborating on the same Kubernetes cluster. This creates a lack of clarity about division of responsibility – if there is a problem with a pod, is that a DevOps problem, or something to be resolved by the relevant application team?

In short – Kubernetes troubleshooting can quickly become a mess, waste major resources and impact users and application functionality – unless teams closely coordinate and have the right tools available.

Troubleshooting Common Kubernetes Errors

If you are experiencing one of these common Kubernetes errors, here’s a quick guide to identifying and resolving the problem:

• CreateContainerConfigError
• ImagePullBackOff or ErrImagePull
• CrashLoopBackOff
• Kubernetes Node Not Ready

CreateContainerConfigError

This error is usually the result of a missing Secret or ConfigMap. Secrets are Kubernetes objects used to store sensitive information like database credentials. ConfigMaps store data as key-value pairs, and are typically used to hold configuration information used by multiple pods.

How to identify the issue

Run kubectl get pods .

Check the output to see if the pod’s status is CreateContainerConfigError

$ kubectl get pods 
NAME                 READY   STATUS                       RESTARTS   AGE
pod-missing-config   0/1     CreateContainerConfigError   0          1m23s

Getting detailed information and resolving the issue

To get more information about the issue, run kubectl describe [name] and look for a message indicating which ConfigMap is missing:

$ kubectl describe pod pod-missing-config 
Warning Failed 34s (x6 over 1m45s) kubelet 
Error: configmap "configmap-3" not found

Now run this command to see if the ConfigMap exists in the cluster.

For example $ kubectl get configmap configmap-3

If the result is null, the ConfigMap is missing, and you need to create it. See the documentation to learn how to create a ConfigMap with the name requested by your pod.

Make sure the ConfigMap is available by running get configmap [name] again. If you want to view the content of the ConfigMap in YAML format, add the flag -o yaml.

Once you have verified the ConfigMap exists, run kubectl get pods again, and verify the pod is in status Running:

$ kubectl get pods
NAME                 READY   STATUS    RESTARTS   AGE
pod-missing-config   0/1     Running   0          1m23s

ImagePullBackOff or ErrImagePull

This status means that a pod could not run because it attempted to pull a container image from a registry, and failed. The pod refuses to start because it cannot create one or more containers defined in its manifest.

How to identify the issue

Run the command kubectl get pods

Check the output to see if the pod status is ImagePullBackOff or ErrImagePull:

$ kubectl get pods
NAME       READY    STATUS             RESTARTS   AGE
mypod-1    0/1      ImagePullBackOff   0          58s

Getting detailed information and resolving the issue

Run the kubectl describe pod [name] command for the problematic pod.

The output of this command will indicate the root cause of the issue. This can be one of the following:

• Wrong image name or tag—this typically happens because the image name or tag was typed incorrectly in the pod manifest. Verify the correct image name using docker pull, and correct it in the pod manifest.
• Authentication issue in Container registry—the pod could not authenticate with the registry to retrieve the image. This could happen because of an issue in the Secret holding credentials, or because the pod does not have an RBAC role that allows it to perform the operation. Ensure the pod and node have the appropriate permissions and Secrets, then try the operation manually using docker pull.

CrashLoopBackOff

This issue indicates a pod cannot be scheduled on a node. This could happen because the node does not have sufficient resources to run the pod, or because the pod did not succeed in mounting the requested volumes.

How to identify the issue

Run the command kubectl get pods.

Check the output to see if the pod status is CrashLoopBackOff

$ kubectl get pods
NAME       READY    STATUS             RESTARTS   AGE
mypod-1    0/1      CrashLoopBackOff   0          58s

Getting detailed information and resolving the issue

Run the kubectl describe pod [name] command for the problematic pod:

The output will help you identify the cause of the issue. Here are the common causes:

• Insufficient resources—if there are insufficient resources on the node, you can manually evict pods from the node or scale up your cluster to ensure more nodes are available for your pods.
• Volume mounting—if you see the issue is mounting a storage volume, check which volume the pod is trying to mount, ensure it is defined correctly in the pod manifest, and see that a storage volume with those definitions is available.
• Use of hostPort—if you are binding pods to a hostPort, you may only be able to schedule one pod per node. In most cases you can avoid using hostPort and use a Service object to enable communication with your pod.

Kubernetes Node Not Ready

When a worker node shuts down or crashes, all stateful pods that reside on it become unavailable, and the node status appears as NotReady.

If a node has a NotReady status for over five minutes (by default), Kubernetes changes the status of pods scheduled on it to Unknown, and attempts to schedule it on another node, with status ContainerCreating.

How to identify the issue

Run the command kubectl get nodes.

Check the output to see is the node status is NotReady

NAME        STATUS      AGE    VERSION
mynode-1    NotReady    1h     v1.2.0

To check if pods scheduled on your node are being moved to other nodes, run the command get pods.

Check the output to see if a pod appears twice on two different nodes, as follows:

NAME       READY    STATUS               RESTARTS      AGE    IP        NODE
mypod-1    1/1      Unknown              0             10m    [IP]      mynode-1
mypod-1    0/1      ContainerCreating    0             15s    [none]    mynode-2

Resolving the issue

If the failed node is able to recover or is rebooted by the user, the issue will resolve itself. Once the failed node recovers and joins the cluster, the following process takes place:

1. The pod with Unknown status is deleted, and volumes are detached from the failed node.
2. The pod is rescheduled on the new node, its status changes from Unknown to ContainerCreating and required volumes are attached.
3. Kubernetes uses a five-minute timeout (by default), after which the pod will run on the node, and its status changes from ContainerCreating to Running.

If you have no time to wait, or the node does not recover, you’ll need to help Kubernetes reschedule the stateful pods on another, working node. There are two ways to achieve this:

• Remove failed node from the cluster—using the command kubectl delete node [name]
• Delete stateful pods with status unknown—using the command kubectl delete pods [pod_name] --grace-period=0 --force -n [namespace]

Learn more about Node Not Ready issues in Kubernetes.

Troubleshooting Kubernetes Pods: A Quick Guide

If you’re experiencing an issue with a Kubernetes pod, and you couldn’t find and quickly resolve the error in the section above, here is how to dig a bit deeper. The first step to diagnosing pod issues is running kubectl describe pod [name].

Understanding the Output of the kubectl describe pod Command

Here is example output of the describe pod command, provided in the Kubernetes documentation:

Name:		nginx-deployment-1006230814-6winp
Namespace:	default
Node:		kubernetes-node-wul5/10.240.0.9
Start Time:	Thu, 24 Mar 2016 01:39:49 +0000
Labels:		app=nginx,pod-template-hash=1006230814
Annotations:    kubernetes.io/created-by={"kind":"SerializedReference","apiVersion":"v1","reference":{"kind":"ReplicaSet","namespace":"default","name":"nginx-deployment-1956810328","uid":"14e607e7-8ba1-11e7-b5cb-fa16" ...
Status:		Running
IP:		10.244.0.6
Controllers:	ReplicaSet/nginx-deployment-1006230814
Containers:
  nginx:
    Container ID:	docker://90315cc9f513c724e9957a4788d3e625a078de84750f244a40f97ae355eb1149
    Image:		nginx
    Image ID:		docker://6f62f48c4e55d700cf3eb1b5e33fa051802986b77b874cc351cce539e5163707
    Port:		80/TCP
    QoS Tier:
      cpu:	Guaranteed
      memory:	Guaranteed
    Limits:
      cpu:	500m
      memory:	128Mi
    Requests:
      memory:		128Mi
      cpu:		500m
    State:		Running
      Started:		Thu, 24 Mar 2016 01:39:51 +0000
    Ready:		True
    Restart Count:	0
    Environment:        [none]
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-5kdvl (ro)
Conditions:
  Type          Status
  Initialized   True
  Ready         True
  PodScheduled  True
Volumes:
  default-token-4bcbi:
    Type:	Secret (a volume populated by a Secret)
    SecretName:	default-token-4bcbi
    Optional:   false
QoS Class:      Guaranteed
Node-Selectors: [none]
Tolerations:    [none]
Events:
  FirstSeen	LastSeen	Count	From					SubobjectPath		Type		Reason		Message
  ---------	--------	-----	----					-------------		--------	------		-------
  54s		54s		1	{default-scheduler }						Normal		Scheduled	Successfully assigned nginx-deployment-1006230814-6winp to kubernetes-node-wul5
  54s		54s		1	{kubelet kubernetes-node-wul5}	spec.containers{nginx}	Normal		Pulling		pulling image "nginx"
  53s		53s		1	{kubelet kubernetes-node-wul5}	spec.containers{nginx}	Normal		Pulled		Successfully pulled image "nginx"
  53s		53s		1	{kubelet kubernetes-node-wul5}	spec.containers{nginx}	Normal		Created		Created container with docker id 90315cc9f513
  53s		53s		1	{kubelet kubernetes-node-wul5}	spec.containers{nginx}	Normal		Started		Started container with docker id 90315cc9f513

We bolded the most important sections in the describe pod output:

• Name—below this line are basic data about the pod, such as the node it is running on, its labels and current status.
• Status—this is the current state of the pod, which can be:
  • Pending
  • Running
  • Succeeded
  • Failed
  • Unknown
• Containers—below this line is data about containers running on the pod (only one in this example, called nginx),
• Containers:State—this indicates the status of the container, which can be:
  • Waiting
  • Running
  • Terminated
• Volumes—storage volumes, secrets or ConfigMaps mounted by containers in the pod.
• Events—recent events occurring on the pod, such as images pulled, containers created and containers started.

Continue debugging based on the pod state.

Pod Stays Pending

If a pod’s status is Pending for a while, it could mean that it cannot be scheduled onto a node. Look at the describe pod output, in the Events section. Try to identify messages that indicate why the pod could not be scheduled. For example:

• Insufficient resources in the cluster—the cluster may have insufficient CPU or memory resources. This means you’ll need to delete some pods, add resources on your nodes, or add more nodes.
• Resource requirements—the pod may be difficult to schedule due to specific resources requirements. See if you can release some of the requirements to make the pod eligible for scheduling on additional nodes.

Pod Stays Waiting

If a pod’s status is Waiting, this means it is scheduled on a node, but unable to run. Look at the describe pod output, in the ‘Events’ section, and try to identify reasons the pod is not able to run.

Most often, this will be due to an error when fetching the image. If so, check for the following:

• Image name—ensure the image name in the pod manifest is correct
• Image available—ensure the image is really available in the repository
• Test manually—run a docker pull command on the local machine, ensuring you have the appropriate permissions, to see if you can retrieve the image

Pod Is Running but Misbehaving

If a pod is not running as expected, there can be two common causes: error in pod manifest, or mismatch between your local pod manifest and the manifest on the API server.

Checking for an error in your pod description

It is common to introduce errors into a pod description, for example by nesting sections incorrectly, or typing a command incorrectly.

Try deleting the pod and recreating it with kubectl apply --validate -f mypod1.yaml

This command will give you an error like this if you misspelled a command in the pod manifest, for example if you wrote continers instead of containers:

46757 schema.go:126] unknown field: continers
46757 schema.go:129] this may be a false alarm, see https://github.com/kubernetes/kubernetes/issues/5786
pods/mypod1

Checking for a mismatch between local pod manifest and API Server

It can happen that the pod manifest, as recorded by the Kubernetes API Server, is not the same as your local manifest—hence the unexpected behavior.

Run this command to retrieve the pod manifest from the API server and save it as a local YAML file:

kubectl get pods/[pod-name] -o yaml > apiserver-[pod-name].yaml

You will now have a local file called apiserver-[pod-name].yaml, open it and compare with your local YAML. There are three possible cases:

• Local YAML has the same lines as API Server YAML, and more—this indicates a mismatch. Delete the pod and rerun it with the local pod manifest (assuming it is the correct one).
• API Server YAML has the same lines as local YAML, and more—this is normal, because the API Server can add more lines to the pod manifest over time. The problem lies elsewhere.
• Both YAML files are identical—again, this is normal, and means the problem lies elsewhere.

Diagnosing Other Pod Issues

If you weren’t able to diagnose your pod issue using the methods above, there are several additional methods to perform deeper debugging of your pod:

• Examining Pod Logs
• Debugging with Container Exec
• Debugging with an Ephemeral Debug Container
• Running a Debug Pod on the Node

Examining Pod Logs

You can retrieve logs for a malfunctioning container using this command:

kubectl logs [pod-name] [container-name]

If the container has crashed, you can use the --previous flag to retrieve its crash log, like so:

kubectl logs --previous [pod-name] [container-name]

Debugging with Container Exec

Many container images contain debugging utilities—this is true for all images derived from Linux and Windows base images. This allows you to run commands in a shell within the malfunctioning container, as follows:

kubectl exec [pod-name] -c [container-name] -- [your-shell-commands]

Debugging with an Ephemeral Container

There are several cases in which you cannot use the kubectl exec command:

• The container has already crashed
• The container image is distroless, or purposely does not include a debugging utility

The solution, supported in Kubernetes v.1.18 and later, is to run an “ephemeral container”. This is a container that runs alongside your production container and mirrors its activity, allowing you to run shell commands on it, as if you were running them on the real container, and even after it crashes.

Create an ephemeral container using kubectl debug -it [pod-name] --image=[image-name] --target=[pod-name].

The --target flag is important because it lets the ephemeral container communicate with the process namespace of other containers running on the pod.

After running the debug command, kubectl will show a message with your ephemeral container name—take note of this name so you can work with the container:

Defaulting debug container name to debugger-8xzrl

You can now run kubectl exec on your new ephemeral container, and use it to debug your production container.

Running a Debug Pod on the Node

If none of these approaches work, you can create a special pod on the node, running in the host namespace with host privileges. This method is not recommended in production environments for security reasons.

Run a special debug pod on your node using kubectl debug node/[node-name] -it --image=[image-name].

After running the debug command, kubectl will show a message with your new debugging pod—take note of this name so you can work with it:

Creating debugging pod node-debugger-mynode-pdx84 with container debugger on node [node-name]

Note that the new pod runs a container in the host IPC, Network, and PID namespaces. The root filesystem is mounted at /host.

When finished with the debugging pod, delete it using kubectl delete pod [debug-pod-name].

Troubleshooting Kubernetes Clusters: A Quick Guide

Viewing Basic Cluster Info

The first step to troubleshooting container issues is to get basic information on the Kubernetes worker nodes and Services running on the cluster.

To see a list of worker nodes and their status, run kubectl get nodes --show-labels. The output will be something like this:

NAME      STATUS    ROLES    AGE     VERSION        LABELS
worker0   Ready     [none]   1d      v1.13.0        ...,kubernetes.io/hostname=worker0
worker1   Ready     [none]   1d      v1.13.0        ...,kubernetes.io/hostname=worker1
worker2   Ready     [none]   1d      v1.13.0        ...,kubernetes.io/hostname=worker2

To get information about Services running on the cluster, run:

kubectl cluster-info


The output will be something like this:

Kubernetes master is running at https://104.197.5.247
elasticsearch-logging is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy
kibana-logging is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/kibana-logging/proxy
kube-dns is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/kube-dns/proxy

Retrieving Cluster Logs

To diagnose deeper issues with nodes on your cluster, you will need access to logs on the nodes. The following table explains where to find the logs.

Common Cluster Failure Scenarios and How to Resolve Them

Let’s look at several common cluster failure scenarios, their impact, and how they can typically be resolved. This is not a complete guide to cluster troubleshooting, but can help you resolve the most common issues.

API Server VM Shuts Down or Crashes

• Impact: If the API server is down, you will not be able to start, stop, or update pods and services.
• Resolution: Restart the API server VM.
• Prevention: Set the API server VM to automatically restart, and set up high availability for the API server.

Control Plane Service Shuts Down or Crashes

• Impact: Services like the Replication Controller Manager, Scheduler, and so on are collocated with the API Server, so if any of them shut down or crashes, the impact is the same as shutdown of the API Server.
• Resolution: Same as API Server VM Shuts Down.
• Prevention: Same as API Server VM Shuts Down.

API Server Storage Lost

• Impact: API Server will fail to restart after shutting down.
• Resolution: Ensure storage is working again, manually recover the state of the API Server from backup, and restart it.
• Prevention: Ensure you have a readily available snapshot of the API Server. Use reliable storage, such as Amazon Elastic Block Storage (EBS), which survives shut down of the API Server VM, and prefer highly available storage.

Worker Node Shuts Down

• Impact: Pods on the node stop running, the Scheduler will attempt to run them on other available nodes. The cluster will now have less overall capacity to run pods.
• Resolution: Identify the issue on the node, bring it back up and register it with the cluster.
• Prevention: Use a replication control or a Service in front of pods, to ensure users are not impacted by node failures. Design applications to be fault tolerant.

Kubelet Malfunction

• Impact: If the kubelet crashes on a node, you will not be able to start new pods on that node. Existing pods may or may not be deleted, and the node will be marked unhealthy.
• Resolution: Same as Worker Node Shuts Down.
• Prevention: Same as Worker Node Shuts Down.

Unplanned Network Partitioning Disconnecting Some Nodes from the Master

• Impact: The master nodes think that nodes in the other network partition are down, and those nodes cannot communicate with the API Server.
• Resolution: Reconfigure the network to enable communication between all nodes and the API Server.
• Prevention: Use a networking solution that can automatically reconfigure cluster network parameters.

Human Error by Cluster Operator

• Impact: An accidental command by a human operator, or misconfigured Kubernetes components, can cause loss of pods, services, or control plane components. This can result in disruption of service to some or all nodes.
• Resolution: Most cluster operator errors can be resolved by restoring the API Server state from backup.
• Prevention: Implement a solution to automatically review and correct configuration errors in your Kubernetes clusters.

Kubernetes Troubleshooting with Komodor

The troubleshooting process in Kubernetes is complex and, without the right tools, can be stressful, ineffective and time-consuming. Some best practices can help minimize the chances of things breaking down, but eventually, something will go wrong – simply because it can.

This is the reason why we created Komodor, a tool that helps dev and ops teams stop wasting their precious time looking for needles in (hay)stacks every time things go wrong.

Acting as a single source of truth (SSOT) for all of your k8s troubleshooting needs, Komodor offers:

• Change intelligence: Every issue is a result of a change. Within seconds we can help you understand exactly who did what and when.
• In-depth visibility: A complete activity timeline, showing all code and config changes, deployments, alerts, code diffs, pod logs and etc. All within one pane of glass with easy drill-down options.
• Insights into service dependencies: An easy way to understand cross-service changes and visualize their ripple effects across your entire system.
• Seamless notifications: Direct integration with your existing communication channels (e.g., Slack) so you’ll have all the information you need, when you need it.

If you are interested in checking out Komodor, use this link to sign up for a Free Trial.

Learn more about Kubernetes Troubleshooting

There’s a lot more to learn about Kubernetes troubleshooting. Check out some of the most common errors, their causes, and how to fix them.

How to Fix CrashLoopBackOff Kubernetes Error

CrashLoopBackOff appears when a pod is constantly crashing in an endless loop in Kubernetes. Understand and learn how to quickly fix the CrashLoopBackOff error (diagnosis and resolution).

Read more: How to Fix CrashLoopBackOff Kubernetes Error

How to Fix ErrImagePull and ImagePullBackoff

ImagePullBackOff / ErrImagePull error means that a pod cannot pull an image from a container registry. In this article, we walk through the steps you should take to troubleshoot the error.

Read more: How to Fix ErrImagePull and ImagePullBackoff

How to Fix CreateContainerError & CreateContainerConfigError

Kubernetes errors such as CreateContainerConfigError and CreateContainerError occur when a container is created in a pod and fails to enter the Running state. Learn more about these errors and how to fix them quickly.

Read more: How to Fix CreateContainerError & CreateContainerConfigError

How to Fix Kubernetes ‘Node Not Ready’ Error

Node Not Ready error indicates a machine in a K8s cluster that cannot run pods. This error is frequently caused by a lack of resources on the node, an issue with the kubelet, or a kube-proxy error.

Read more: How to Fix Kubernetes ‘Node Not Ready’ Error

How to Fix OOMKilled Kubernetes Error (Exit Code 137)

OOMKilled (exit code 137) occur when K8s pods are killed because they use more memory than their limits. OOM stands for “Out Of Memory”, a tool available on Linux systems that keeps track of how much memory each process uses.

Read more: How to Fix OOMKilled Kubernetes Error (Exit Code 137)

Kubernetes Health Checks

This article discusses how to set up a reliable health check process and why health checks are essential for K8s troubleshooting. We go through the different types of health checks including kubelet, liveness, readiness probes, and more.

Read more: Kubernetes Health Checks: Everything You Need to Know

See Additional Guides on Key Kubernetes Topics

Together with our content partners, we have authored in-depth guides on several other topics that can also be useful as you explore the world of Kubernetes.

Read our guide to Kubernetes resource quota

Read our guide to change intelligence

Kubernetes Troubleshooting

Authored by Komodor

• Kubernetes CrashLoopBackOff Error: What It Is and How to Fix It 
• Kubernetes Health Checks: Everything You Need to Know
• How to Fix CreateContainerError & CreateContainerConfigError 

Kubernetes Architecture

Authored by Komodor

• What Are Kubernetes Services? The Ultimate Guide 
• Kubernetes Dashboard: Quick Guide and 4 Great Alternatives
• Ultimate Guide to Kubernetes Operators and How to Create New Operators

Kubernetes Performance

Authored by Granulate

• Kubernetes VPA: How It Works, HPA vs. VPA & 7 Best Practices
• Cluster Autoscaler Basics, Pros and Cons & 8 Best Practices
• Granulate Real-Time Continuous Kubernetes & Containers Optimization