How To Troubleshoot Kubernetes Pods ?

Kubernetes (K8s) installations frequently present issues from multiple perspectives, including pods, services, ingress, non-responsive clusters, control planes, and high-availability configurations. Kubernetes pods are the smallest deployable units in the Kubernetes ecosystem, each containing one or more containers that share resources and a network. Pods are intended to execute a single instance of an app or process and are built and destroyed as required. Pods are essential for scaling, updating, and sustaining applications in a Kubernetes environment.

In this article, we will explore Pod troubleshooting strategies in Kubernetes, offering expert insights to help you ensure the seamless performance of your applications.

What is Kubernetes Troubleshooting?

Kubernetes troubleshooting is the process of finding, diagnosing, and resolving issues with Kubernetes clusters, nodes, pods, or containers. Kubernetes troubleshooting, as a broader term, encompasses effective ongoing fault management and preventative measures for Kubernetes components.

Kubernetes troubleshooting can be extremely difficult. This article will address frequent issues like

• CreateContainerConfigError, ImagePullBackOff, CrashLoopBackOff, and Kubernetes Node Not Ready.
• Explaining the basic diagnosis of issues with Kubernetes pods.
• Showing where to get logs and other data needed for further investigation.

The Three Pillars of Kubernetes Troubleshooting

There are three aspects to effective troubleshooting in a Kubernetes cluster: understanding the problem, managing and remediating the problem, and preventing the problem from recurring.

Understanding the problem

In a Kubernetes context, it can be difficult to understand what happened and identify the core cause of the issue. This often includes:

• Review recent changes to the afflicted cluster, pod, or node to determine what caused the issue.
• Analyzing YAML configurations, Github repositories, and logs from VMs or bare metal machines executing the faulty components.
• Analyzing Kubernetes events and metrics such as disk pressure, memory pressure, and utilization. In a mature environment, dashboards should provide critical metrics for clusters, nodes, pods, and containers across time.
• Comparing similar components that behave similarly, as well as assessing dependency relationships between components, to determine whether they are related to the failure.

Managing and Remediating the Problem

In a microservices architecture, it is common for each component to be developed and managed by a separate team. Because production incidents often involve multiple components, collaboration is essential to remediate problems quickly.

Once the problem is identified, there are three techniques to resolving it:

• Ad hoc solutions: based on tribal knowledge among teams working on the impacted components. Often, the engineer who created the component will have unwritten knowledge of how to troubleshoot and resolve it.
• Manual runbooks: Manual runbooks are explicit, written procedures for resolving different types of incidents. A runbook ensures that each member of the team can swiftly tackle the issue.
• Automated runbooks: Automated runbooks are automated processes that are launched automatically when a problem is discovered. They can be implemented as a script, infrastructure as code (IaC) template, or Kubernetes operator. It can be difficult to automate reactions to all typical situations, but it can be extremely advantageous by minimizing downtime and eliminating human mistake.

Prevention

Successful teams make prevention their top priority. Over time, this will reduce the time invested in identifying and troubleshooting new issues. Preventing production issues in Kubernetes involves:

• Developing policies, regulations, and playbooks following each occurrence to guarantee effective remediation.
• Investigating if and how to automate a response to the issue.
• Defining how to quickly identify the issue next time and make the required data available—for example, by instrumenting the relevant components.
• Ensure that the issue is escalated to the proper teams, and that those teams can effectively communicate to resolve it.

Types of Pod Errors

Before diving into pod debugging, it’s essential to understand different types of Pod errors.

Container & Image Errors

All these error states are part of the kubernetes container package & Kubernetes image package.

Following is the list of official Kubernetes pod errors with error descriptions.

Pod Error Type	Error Description
ErrImagePull	If kubernetes is not able to pull the image mentioned in the manifest.
ErrImagePullBackOff	Container image pull failed, kubelet is backing off image pull
ErrInvalidImageName	Indicates a wrong image name.
ErrImageInspect	Unable to inspect the image.
ErrImageNeverPull	Specified Image is absent on the node and PullPolicy is set to NeverPullImage
ErrRegistryUnavailable	HTTP error when trying to connect to the registry
ErrContainerNotFound	The specified container is either not present or not managed by the kubelet, within the declared pod.
ErrRunInitContainer	Container initialization failed.
ErrRunContainer	Pod’s containers don’t start successfully due to misconfiguration.
ErrKillContainer	None of the pod’s containers were killed successfully.
ErrCrashLoopBackOff	A container has terminated. The kubelet will not attempt to restart it.
ErrVerifyNonRoot	A container or image attempted to run with root privileges.
ErrCreatePodSandbox	Pod sandbox creation did not succeed.
ErrConfigPodSandbox	Pod sandbox configuration was not obtained.
ErrKillPodSandbox	A pod sandbox did not stop successfully.
ErrSetupNetwork	Network initialization failed.

How to Troubleshoot Pod Errors ?

The first step in troubleshooting a pod is getting the status of the pod. Run the below command to know the status of the pods.

kubectl get pods

Now that you know the error type, describe the individual pod and look through the events to see what is generating the pod error.

To get detailed information about the pod. Run the below command.

kubectl describe pod <pod-name>

Now let’s look at some of the most common pod errors and how to troubleshoot them.

Troubleshoot ErrImagePullBackOff

Run the below command to get the pod details.

kubectl get pods

If you see ErrImagePullBackOff in pod status, it is most likely for the following reasons.

• The supplied image does not exist in the registry.
• A misspelling in the image’s name or tag.
• Image pull access was denied from the given registry due to credential issues.

If you check the pod events, you will see the ErrImagePull error followed by ErrImagePullBackOff. This means the kubelet stops trying to pull the image again and again.

kubectl describe pod <pod-name>

• Error reference

1. Troubleshoot Error: InvalidImageName

Run below command to know status of the pods.

kubectl get pods

• If you specify a wrong image URL in the manifest, you will get the InvalidImageName error.

For example, if you have a private container registry and you mention the image name with https, it will throw the ‘InvalidImageName’ error. You need to specify the image name without https.

• If you have trailing slashes in the image name, you will get both ‘InspectFailed’ & ‘InvalidImageName’ errors. You can check it by describing the pod.

• Error reference

2. Pod Configmap & Secret Errors[CreateContainerConfigError]

CreateContainerConfigError is one of the common errors related to Configmaps and Secrets in pods.

This normally occurs due to two reasons.

• You have the wrong configmap or secret keys referenced as environment variables
• The referenced configmap is not available

If you describe the pod you will see the following error.

If you have a typo in the key name, you will see the following error in the pod events.

To rectify this issue,

• Ensure the config map is created.
• Ensure you have the correct configmap name & key name added to the env declaration.

Let’s look at the correct example. Here is a configmap where service-name is the key that is needed as an env variable inside the pod.

Here is the correct pod definition using the key (service-name) & configmap name (nginx-config)

Conclusion

Troubleshooting Pod failures in Kubernetes can initially seem daunting. However, with a systematic approach, you can identify and solve most issues. Always start with the basics: check the Pod status, describe the Pod for details, examine logs, and inspect configurations. Remember, every failure is an opportunity to learn and improve your Kubernetes skills.

Kubernetes Pods – FAQ’s

what are some common issues with Kubernetes pods?

Some of the common issues with pods includes resource constraints, Container crashes, misconfigured environment variables and networking problems.

What should we do when a pod is stuck in pending state?

Pods remain in a pending state when there are insufficient resources or scheduling issues. To get more information about why the pod is in pending state you can use the command ‘kubectl describe pod <pod-name>’

What are Kubernetes pods?

Pods are smallest unit of deployment in kubernetes, consisting of one or more containers which share resources like network & storage

What to do when my pod’s containers are not starting or crashing?

Review the container images, their dependencies and configurations. Check the logs for any startup errors

How can I troubleshoot issues related to networking?

You have to verify network policies, service configurations and pod network plugins. Test the connectivity using ‘kubectl exec’ command and then inspect DNS resolution.