Kubernetes ImagePullBackOff Error

Kubernetes is a portable, extensible, open-source platform for managing containerized workloads and services that facilitates both declarative configuration and automation. In this context, I used minikube, which is a lightweight Kubernetes implementation that creates a virtual machine on my local machine and deploys a simple cluster containing only one node. When running containers on Kubernetes, if a container image does not already exist on a Node, kubelet will instruct the container runtime to pull it. ImagePullBackOff means that a Pod couldn't start because Kubernetes could not pull the container Image. The 'BackOff' part means that Kubernetes will keep trying to pull the image, with an increasing delay.

The root causes of this ImagePullBackOff error include:

• The image or tag does not exist
• A typo was made in the image name or tag
• The image registry requires authentication
• You have exceeded a rate or download limit on the registry.

The first step to finding out the root cause of the error is kubectl describe. This will show the full error log of the Pod, so you can see what is causing the error. In some cases, like my example, the pod might be in a different namespace so the namespace has to be indicated

kubectl describe pods --namespace <namespace>

After confirming the root of the problem, check the spread of the problem

• Are there other Pods already running in that node and are they pulling from the same registry? what is different about this pod?
• Can the node in the cluster pull the image?
• Can you pull the image locally from your workstation using docker pull or podman pull?

If the image can be pulled locally, add this line of code:

ImagePullPolicy: IfNotPresent

This means the image will only be pulled if it is not already present locally. Other options for this ImagePullPolicy include, Never and Always. You can check the Kubernetes documentation for more information about images.

In some cases, while working with node images, I came across this error. Pulling the image locally first and then taking out the tag of the image solved this problem. Meaning if the image name was:

Image: node:14

change to 

Image: node

Kubernetes is now the second largest open-source project right after Linux. It makes container orchestration easy and some of its perks include service discovery and load balancing, automatic rollouts and rollbacks, and self-healing amongst others. Using Kubernetes for your containers is an idea that should be considered.