Kubernetes ImagePullBackOff

What Is Kubernetes ImagePullBackOff Error and How to Fix It

What Is Kubernetes ImagePullBackOff? 

The ImagePullBackOff error is a common error message in Kubernetes that occurs when a container running in a pod fails to pull the required image from a container registry. This error can occur for a variety of reasons, including network connectivity issues, incorrect image name or tag, missing credentials, or insufficient permissions.

When a pod is created, Kubernetes attempts to pull the container image specified in the pod definition from the container registry. If the image is not available or cannot be pulled, Kubernetes marks the pod as “ImagePullBackOff” and stops attempting to pull the image. Thus, the pod will not be able to start and will remain in a pending state.

The root cause of the problem needs to be identified and addressed. This may involve checking network connectivity, verifying the image name and tag, ensuring that credentials are correct and up to date, and ensuring that the appropriate permissions are in place. Once the issue is resolved, the Pod can be recreated, and the container image should be pulled successfully

This is part of a series of articles about Kubernetes troubleshooting

In this article:

Common Reasons for the ImagePullBackOff Error 

There are several common causes of this error, including:

• Invalid name: One common cause of the ImagePullBackOff error is an invalid image name. This can happen if the image name specified in the pod definition is incorrect or does not exist in the container registry. It is important to ensure that the image name is spelled correctly and that it exists in the container registry before attempting to pull it.
• Missing or incorrect tags: Another common cause is a missing or incorrect tag. Images in a container registry are typically organized using tags to indicate specific versions or releases. If the image tag is missing or incorrect in the pod definition, Kubernetes will not be able to pull the correct image. It is important to ensure that the correct tag is specified in the pod definition.
• Inaccurate credentials or registry information: Kubernetes requires valid authentication credentials to pull images from private container registries. If the credentials specified in the pod definition are inaccurate or outdated, Kubernetes cannot authenticate to the container registry or pull the image. It is important to ensure that the credentials used to access the container registry are correct and up to date.
• Network connectivity issues: The ImagePullBackOff error can also occur when there are issues in the connectivity between the container registry and the Kubernetes cluster. If there is a firewall blocking the connection or a slow network connection, Kubernetes may not be able to download the image from the container registry. It is important to ensure that there are no network connectivity issues and that the Kubernetes cluster can access the container registry.
• Reaching the container registry rate limit: Some container registries limit the number of requests that can be made to their API in a given period of time. If the Kubernetes cluster exceeds this rate limit, the ImagePullBackOff error may occur. In this case, it is important to ensure that the Kubernetes cluster is not exceeding the rate limit and to contact the container registry to request a higher rate limit if needed.

How to Troubleshoot and Fix the ImagePullBackOff Error 

Troubleshooting and fixing the ImagePullBackOff error in Kubernetes can be a complex task, but the following steps are the general way to identify and resolve the issue:

Step 1: Collect information

The first step in troubleshooting the ImagePullBackOff error is to collect information about the problem. Use the kubectl describe podcommand to retrieve the information and save it as a text file:

kubectl describe pod [podname] > /tmp/troubleshooting_pod_description.txt

Step 2: Check the Events section in the pod description 

The events section in the pod description text file can be a valuable source of information for troubleshooting errors like ImagePullBackOff. This section provides details about the status of the pod and any events that have occurred, including errors related to image pulling. 

Check for messages such as Repository does not exist, No pull access, Manifest not found, and Authorization failed. These events can provide clues as to the root cause of the ImagePullBackOff error.

You can use grepor a text editor such as Nano to search for the above errors.

Step 3: Troubleshoot and fix the error

Once you have collected information and reviewed the events section, you can begin to troubleshoot the issue. For example, if the error message is Repository does not exist, it indicates that the container registry does not exist or is not accessible. Kubernetes pulls images from Docker Hub by default, so this error could occur if the cluster is using a private registry. To resolve this issue, ensure that the container registry is available and that the pod definition specifies the correct registry URL.

If the error message is Manifest not found, Kubernetes could not find the requested version of the container image in the specified registry. To resolve this issue, ensure that the image name and tag are correct and that the image has been pushed to the container registry. If the image has been deleted or moved, update the pod definition with the correct image name and tag.

If the error message is Authorization failed, the credentials used to access the container registry are incorrect or expired. To resolve this issue, update the pod definition with the correct credentials or generate new credentials if the old ones have expired. Verify that the credentials (secrets) are correct and that the pod has the appropriate permissions to access the container registry.

Step 4: Recreate the pod

Once the issue has been identified and addressed, you can attempt to resolve the ImagePullBackOff error by deleting and recreating the pod. To do this, run the following commands:

kubectl delete pod <pod_name>

kubectl apply -f <pod_definition_file>

This will delete the existing pod and recreate it with the updated definition file. If the image is now available and the issue has been resolved, the pod should start successfully.

Kubernetes Troubleshooting with Lumigo

Lumigo is a troubleshooting platform, purpose-built for microservice-based applications. Developers using Kubernetes to orchestrate their containerized applications can use Lumigo to monitor, trace and troubleshoot issues fast. Deployed with zero-code changes and automated in one-click, Lumigo stitches together every interaction between micro and managed service into end-to-end stack traces. These traces, served alongside request payload data, give developers complete visibility into their container environments. Using Lumigo, developers get:

• End-to-end virtual stack traces across every micro and managed service that makes up a serverless application, in context
• API visibility that makes all the data passed between services available and accessible, making it possible to perform root cause analysis without digging through logs 
• Distributed tracing that is deployed with no code and automated in one click 
• Unified platform to explore and query across microservices, see a real-time view of applications, and optimize performance

To try Lumigo for Kubernetes, check out our Kubernetes operator on GitHub.

Learn more about Lumigo