How do I force Kubernetes to re-pull an image

Question

I have the following replication controller in Kubernetes on GKE   apiVersion  v1 kind  ReplicationController metadata    name  myapp   labels      app  myapp spec    replicas  2   selector      app  myapp     deployment  initial   template      metadata        labels          app  myapp         deployment  initial     spec        containers        - name  myapp         image  myregistry com myapp 5c3dda6b         ports          - containerPort  80       imagePullPolicy  Always       imagePullSecrets          - name  myregistry com-registry-key   Now  if I say  kubectl rolling-update myapp --image us gcr io project-107012 myapp 5c3dda6b   the rolling update is performed  but no re-pull   Why

User · Answer

The rolling update command  when given an image argument  assumes that the image is different than what currently exists in the replication controller

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Now  the command kubectl rollout restart deploy YOUR-DEPLOYMENT combined with a imagePullPolicy  Always policy will allow you to restart all your pods with a latest version of your image

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My hack during development is to change my Deployment manifest to add the latest tag and always pull like so   image  etoews my-image latest imagePullPolicy  Always   Then I delete the pod manually  kubectl delete pod my-app-3498980157-2zxhd   Because it s a Deployment  Kubernetes will automatically recreate the pod and pull the latest image

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Specify strategy as     strategy       type  Recreate     rollingUpdate  null   Make sure you have different annotation for each deployment  Helm does it like     template      metadata        labels          app kubernetes io name  AppName         app kubernetes io instance  ReleaseName       annotations          rollme     randAlphaNum 5   quote      Specify image pull policy - Always        containers          - name      Chart Name              image   quot     Values image repository        Values image tag    quot            imagePullPolicy  Always

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Linux  kubectl patch deployment  lt name gt  -p     spec      template      metadata      annotations      date      date    s              windows  kubectl patch deployment  lt name gt  -p  -join      spec        template        metadata        annotations        date             Get-Date -Format o  replace      -   replace

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One has to group imagePullPolicy inside the container data instead of inside the spec data   However  I filed an issue about this because I find it odd   Besides  there is no error message   So  this spec snippet works   spec    containers    - name  myapp     image  myregistry com myapp 5c3dda6b     ports      - containerPort  80     imagePullPolicy  Always   imagePullSecrets      - name  myregistry com-registry-key

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This answer aims to force an image pull in a situation where your node has already downloaded an image with the same name  therefore even though you push a new image to container registry  when you spin up some pods  your pod says  quot image already present quot   For a case in Azure Container Registry  probably AWS and GCP also provides this    You can look to your Azure Container Registry and by checking the manifest creation date you can identify what image is the most recent one   Then  copy its digest hash  which has a format of sha256 xxx   xxx    You can scale down your current replica by running command below  Note that this will obviously stop your container and cause downtime    kubectl scale --replicas 0 deployment  lt deployment-name gt  -n  lt namespace-name gt    Then you can get the copy of the deployment yaml by running   kubectl get deployments apps  lt deployment-name gt  -o yaml  gt  deployment yaml   Then change the line with image field from  lt image-name gt   lt tag gt  to  lt image-name gt  sha256 xxx   xxx  save the file   Now you can scale up your replicas again  New image will be pulled with its unique digest    Note  It is assumed that  imagePullPolicy  Always field is present in the container

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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  It leaves you flawless update without any problem  mainly when you have a persistent volume attached to the pod

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You can define imagePullPolicy  Always in your deployment file

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There is a comand to directly do that  Create a new kubectl rollout restart command that does a rolling restart of a deployment  The pull request got merged  It is part of the version 1 15  changelog  or higher

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Apparently now when you run a rolling-update with the --image argument the same as the existing container image  you must also specify an --image-pull-policy  The following command should force a pull of the image when it is the same as the container image   kubectl rolling-update myapp --image us gcr io project-107012 myapp 5c3dda6b --image-pull-policy Always

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A popular workaround is to patch the deployment with a dummy annotation  or label     kubectl patch deployment  lt name gt  -p         spec      template      metadata      annotations      date      date    s             Assuming your deployment meets these requirements  this will cause K8s to pull any new image and redeploy

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Kubernetes will pull upon Pod creation if either  see updating-images doc     Using images tagged  latest imagePullPolicy  Always is specified   This is great if you want to always pull  But what if you want to do it on demand  For example  if you want to use some-public-image latest but only want to pull a newer version manually when you ask for it  You can currently    Set imagePullPolicy to IfNotPresent or Never and pre-pull  Pull manually images on each cluster node so the latest is cached  then do a kubectl rolling-update or similar to restart Pods  ugly easily broken hack   Temporarily change imagePullPolicy  do a kubectl apply  restart the pod  e g  kubectl rolling-update   revert imagePullPolicy  redo a kubectl apply  ugly   Pull and push some-public-image latest to your private repository and do a kubectl rolling-update  heavy     No good solution for on-demand pull  If that changes  please comment  I ll update this answer

[image] How do I force Kubernetes to re-pull an image?

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