Kubernetes, though powerful, is a complex system. Issues ranging from configuration mishaps to version incompatibilities can disrupt your deployment, affecting the efficiency of your applications. Understanding Kubernetes errors and how to troubleshoot them is a critical part of effectively managing a Kubernetes cluster.

What Is Kubernetes Troubleshooting? 

Kubernetes troubleshooting involves identifying and resolving issues that arise when using Kubernetes. These issues can vary from configuration errors to resource constraints, security issues, persistent storage problems, and version incompatibility. Understanding how to identify and fix these issues is crucial for the smooth operation of your applications.

The process of troubleshooting in Kubernetes starts with understanding the symptoms of the problem. This could be an application not running as expected, a service being unavailable, or a resource not being allocated correctly. Once the symptoms are identified, the next step is to diagnose the cause of the problem. This often involves reviewing logs, examining system metrics, or even diving into the Kubernetes source code.

Once the cause has been identified, the last step is to fix the problem. This could involve making changes to your Kubernetes configuration, scaling your resources, updating your security settings, or even upgrading your Kubernetes version. In the following sections, I will provide a deep dive into common causes of Kubernetes errors and how to fix them.

Common Causes of Kubernetes Errors 

There are several common causes of errors in Kubernetes. Understanding these is the first step towards effective Kubernetes troubleshooting.

  1. Misconfiguration

Kubernetes is a complex system with a multitude of configuration options. A slight misstep in setting these up can result in unexpected behavior or even outright failures. 

Misconfiguration can manifest in several ways. For instance, you might incorrectly set up your Kubernetes networking, causing services to be unreachable. Alternatively, you might misconfigure your pods, causing them to crash or behave erratically. Troubleshooting these issues involves carefully reviewing your configuration files and correcting any errors.

  1. Resource Constraints

Kubernetes operates by allocating resources (such as CPU, memory, and storage) to different components. If these resources are not available or are incorrectly allocated, it can cause problems.

For instance, if a pod is allocated more memory than is available on the node, it can cause the node to become overloaded and crash. Alternatively, if a pod is not given enough CPU, it can cause the pod to run slowly or even fail to start. Troubleshooting these issues often involves scaling your resources to meet demand.

  1. Security and RBAC Issues

Kubernetes uses a system called Role-Based Access Control (RBAC) to manage who can do what within a cluster. Misconfigurations or misunderstandings about how this system works can lead to errors.

If a user or service account doesn't have the right permissions to perform a particular action, Kubernetes will prevent it from happening, resulting in an error. For example, if a pod needs to read data from a particular ConfigMap, but the service account it's running under doesn't have permission to do so, the read operation will fail. Fixing these kinds of issues often involves adjusting the RBAC rules to ensure the right permissions are in place.

  1. Persistent Storage Problems

Kubernetes has a complex system for managing storage, and misconfigurations or misunderstandings about how it works can lead to errors. For example, a pod might fail to start if it's unable to mount a necessary persistent volume. 

Alternatively, data might be lost if a pod writes to a location that isn't backed by persistent storage. Troubleshooting these kinds of issues often involves carefully reviewing your storage configuration and ensuring it's set up correctly.

  1. Version Incompatibility

Kubernetes is a rapidly evolving project, and new versions are released regularly. However, not all versions are compatible with each other, and using incompatible versions can cause problems.

For instance, you might be using a version of a Kubernetes API that has been deprecated in the version of Kubernetes you're running. This can cause your applications to fail. Troubleshooting these issues often involves upgrading your Kubernetes version or updating your applications to use a newer API version.

5 Kubernetes Errors and How to Solve Them 

This section will cover five of the most common Kubernetes errors and their solutions. These errors can be quite frustrating, but with the right knowledge and approach, you can resolve them effectively.

1.CrashLoopBackOff

The CrashLoopBackOff error occurs when a container in Kubernetes cannot start, and Kubernetes continually tries to restart it. Here are the steps to diagnose and resolve this error:

  1. Identification: Use the command kubectl describe pod [pod's name] to identify the issue. The message CrashLoopBackOff in the output indicates that the container is failing to start.
  2. Log review: The next step is to review the logs of the pod to understand why the container is failing to start. Use the command kubectl logs [pod's name] to access the logs.
  3. Solution: The solution to this error varies depending on the cause. It could be due to a configuration error, insufficient resources, or a problem with the application code. You would need to rectify the specific issue to resolve this error.

Learn more in this in-depth guide to the CrashLoopBackOff error.

2.Kubernetes Node Not Ready

This common error means that the Kubernetes node is not in a ready state and cannot receive new pods. Here's how you can troubleshoot this issue:

  1. Identification: Use the command kubectl get nodes to check the status of your nodes. If a node is not ready, it will show 'NotReady' status.
  2. Investigation: Investigate the issue using the command kubectl describe node [node's name]. This will give you detailed information about the node, including any events that might have led to its NotReady status.
  3. Resolution: The solution will depend on the root cause of the problem. It could be due to resource exhaustion, network issues, or problems with the kubelet service. You should address these issues to bring the node back to the ready state.

3.Exit Code 1

Exit Code 1 is another common Kubernetes error, indicating that the container has crashed due to an error in the application running inside it. Here’s how you can troubleshoot this:

  1. Identification: Use the command kubectl describe pod [pod's name] to identify the error. If the container has crashed, the output will show Exit Code 1.
  2. Logs Review: Review the logs of the pod using the command kubectl logs [pod's name]. The logs will provide more information about why the container crashed.
  3. Solution: The solution will depend on the cause of the crash. The error could be due to a bug in the application, a configuration error, or a resource issue. You need to fix these problems to resolve the error.

4.Exit Code 125

Exit Code 125 indicates that the Docker runtime has failed to run the container. This error is less common but can be quite tricky to resolve. Here’s how to troubleshoot this:

  1. Identification: Use the command kubectl describe pod [pod's name] to identify the error. If Docker has failed to run the container, the output will show Exit Code 125.
  2. Investigation: Investigate the issue using Docker. You can check the Docker logs or try running the container manually with Docker to get more information about the problem.
  3. Resolution: The solution could be to fix a configuration issue with Docker, update Docker to a more recent version, or resolve a problem with the container image.

5.Exit Code 137

Exit Code 137 means that the container has been terminated by the kernel due to a lack of resources. Here’s how you can troubleshoot this:

  1. Identification: Use the command kubectl describe pod [pod's name] to identify the error. If the container has been terminated due to a lack of resources, the output will show Exit Code 137.
  2. Investigation: Investigate the resource usage of your pods and nodes. You can use the command kubectl describe node to check the resource usage of your nodes.
  3. Solution: The solution is to allocate more resources to your pods or nodes, or to optimize your application to use resources more efficiently.

Conclusion

Mastering Kubernetes troubleshooting can save you a lot of time and headaches. While the errors discussed in this guide are some of the most common, many more could occur. However, the troubleshooting steps remain the same: identify the problem, investigate its cause, and apply the appropriate solution. This guide should help you handle any Kubernetes error thrown your way.

Author: Gilad David Maayan

Technology writer who has worked for SAP, Imperva, Samsung NEXT, NetApp and Check Point, the head of Agile SEO marketing agency.