Kubernetes ImagePullBackOff Explained

Good day. It's Monday, Sep. 2, and in this issue, we're covering:

• Kubernetes ImagePullBackOff Explained

• Elasticsearch is Open Source, Again

• Grafana 11.2 release: new updates for data sources, visualizations, transformations, and more

• Save ingestion costs by splitting logs into multiple tables

• Kubectl commands and best practices for new users

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Use Case

Kubernetes ImagePullBackOff Explained

For Kubernetes practitioners, encountering the ImagePullBackOff error is a common challenge that is inevitable.

The Kubernetes ImagePullBackOff error happens when the system fails to retrieve the required container image. When this occurs, the container remains in a Waiting state, unable to proceed with deployment.

What exactly happens during an ImagePullBackOff?

• Kubernetes requests the node to pull the image.

• Node sends a request to Docker Daemon to pull the image.

• Docker Daemon requests the image from the registry.

• If the image is found, the registry sends the image back to Docker Daemon.

• Docker Daemon pulls the image to the node.

• If the image is successfully pulled, Kubernetes marks the image as ready.

• If the image is not found, Docker Daemon reports the failure.

• Kubernetes retries pulling the image.

• If the retry fails, Kubernetes enters ImagePullBackOff state, preventing further retries.

How to detect ImagePullBackOff?

1. View Pods Status

Check if the pod is experiencing issues by viewing its status.

$ kubectl get pods
NAME        READY   STATUS         RESTARTS   AGE
api-pod     0/1     ErrImagePull   0          25s 

Wait a moment, then run the get pods command again: Confirm if the status has changed to ImagePullBackOff after a few seconds.

$ kubectl get pods
NAME        READY   STATUS             RESTARTS   AGE
api-pod     0/1     ImagePullBackOff   0          1m5s 

2. Inspect the Pod

Get detailed information on why the image pull is failing.

$ kubectl describe pod api-pod
Events:
Type     Reason     Age                From               Message
----     ------     ----               ----               -------
Normal   Scheduled  50s                default-scheduler  Successfully assigned default/api-pod to minikube
Normal   Pulling    25s (x2 over 45s)  kubelet            Pulling image "techopsexamples.com/api-service:v2.5"
Warning  Failed     15s (x2 over 40s)  kubelet            Failed to pull image "techopsexamples.com/api-service:v2.5": Error response from daemon: pull access denied for example.com/api-service, repository does not exist or may require 'docker login': denied: requested access to the resource is denied
Warning  Failed     15s (x2 over 40s)  kubelet            Error: ErrImagePull
Normal   BackOff    5s (x2 over 40s)   kubelet            Back-off pulling image "techopsexamples.com/api-service:v2.5"
Warning  Failed     5s (x2 over 40s)   kubelet            Error: ImagePullBackOff

Fixing ImagePullBackOff

1. Fix Manifest or Image Name

Correct typos or incorrect image names in the pod manifest.

apiVersion: v1
kind: Pod
metadata:
  name: api-pod
  labels:
    app: api
spec:
  containers:
  - name: api-container
    image: techopsexamples.com/api-service:v2.5
    ports:
    - containerPort: 8080

Apply this manifest again: Apply the corrected manifest to update the pod.

$ kubectl apply -f pod.yaml
pod/api-pod configured

Check pod status: Verify that the pod is now running successfully.

$ kubectl get pods
NAME        READY   STATUS    RESTARTS   AGE
api-pod     1/1     Running   0          1m 

2. Non-existent Image Validation

Ensure the image is available in the registry before pulling.

$ docker push techopsexamples.com/api-service:v2.5

3. Image Registry Authorization

Create a secret with credentials to access the private registry.

$ kubectl create secret docker-registry reg-secret \
  --docker-server=private-repo.com \
  --docker-username=myuser \
  --docker-password=mysecurepassword \
  --docker-email=[email protected]

Link the secret to the pod's manifest to allow access.

apiVersion: v1
kind: Pod
metadata:
  name: private-api-pod
  labels:
    app: private-api
spec:
  containers:
  - name: private-api-container
    image: private-repo.com/internal-app:v3.0
  imagePullSecrets:
  - name: reg-secret

I believe this was helpful !

Next time when you encounter an ImagePullBackOff error, you'll know exactly how to diagnose and fix it efficiently.

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