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I have a Kubernetes deployment which uses image: test:latest (not real image name but it's the latest tag).
This image is on docker hub. I have just pushed a new version of test:latest to dockerhub. I was expecting a new deployment of my pod in Kubernetes but nothing happends.
I've created my deployment like this:
kubectl run sample-app --image=`test:latest` --namespace=sample-app --image-pull-policy Always
Why isn't there a new deployment triggered after the push of a new image?
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Image Pull Policy Options If imagePullPolicy is set to Always, Kubernetes will always pull the image from the Repository. With IfNotPresent, Kubernetes will only pull the image when it does not already exist on the node. While with imagePullPolicy set to Never, Kubernetes will never pull the image.
The Image pull policy will always actually help to pull the image every single time a new pod is created (this can be in any case like scaling the replicas, or pod dies and new pod is created) But if you want to update the image of the current running pod, deployment is the best way.
What Does `Failed to Pull Image` Mean? You'll get a `Failed to pull image` error when Kubernetes tries to create a new pod but can't pull the container image it needs in order to do so. You'll usually see this straight after you try to apply a new resource to your cluster using a command like `kubectl apply`.
To resolve it, double check the pod specification and ensure that the repository and image are specified correctly. If this still doesn't work, there may be a network issue preventing access to the container registry. Look in the describe pod text file to obtain the hostname of the Kubernetes node.
There are three image policy pull options for Kubernetes. If imagePullPolicy is set to Always, Kubernetes will always pull the image from the Repository. With IfNotPresent, Kubernetes will only pull the image when it does not already exist on the node. While with imagePullPolicy set to Never, Kubernetes will never pull the image.
Without the Always policy, Kubernetes would never pull your new image releases if the tag was already available locally. All the policies which permit image pulls will fetch new versions of your locally cached tags. Use an image digest as your Pod’s image field if you want a container to stick with an exact image version each time it starts.
With IfNotPresent, Kubernetes will only pull the image when it does not already exist on the node. While with imagePullPolicy set to Never, Kubernetes will never pull the image. In case the specification is not stated on the manifest file, Kubernetes will set the policy depending on the image’s tag.
You don’t have to specify an image pull policy. When a Pod lacks a policy, Kubernetes will infer your intentions from the image’s tag. If you’ve supplied a specific tag (such as my-image:my-release ), the image will only be pulled if the tag doesn’t already exist on the Kubelet node. This policy is called IfNotPresent.
Kubernetes is not watching for a new version of the image. The image pull policy specifies how to acquire the image to run the container. Always means it will try to pull a new version each time it's starting a container. To see the update you'd need to delete the Pod (not the Deployment) - the newly created Pod will run the new image.
There is no direct way to have Kubernetes automatically update running containers with new images. This would be part of a continuous delivery system (perhaps using kubectl set image with the new sha256sum or an image tag - but not latest).
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One way to force the update to happen is to run this in your CI script (after pushing the new image and with image-pull-policy set to Always in the applied yaml):
kubectl rollout restart deployment/<name> --namespace=<namespace>
In Azure Devops enter "rollout" as the command, use the namespace feature above and put "restart ..." in the parameters field.
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If you are working with yml files, executing deployment with
kubectl apply -f myfile.yml
and
imagePullPolicy: Always
on your file, k8s will not pull a new image. You will first need to delete the pod, and the K8s deployment will automatically pull the image.
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