Re-pulling image in kubernetes

Question

I have set up a kubernetes cluster on GKE.

My replication controller YAML:

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

But if I try and do an rolling update:

kubectl rolling-update myapp --image=us.gcr.io/project-107012/myapp:5c3dda6b

the rolling update is successful but there's no re-pull of the image

Answer 1

There are only two scenarios when kubernetes will pull an image for pod creation(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:

This works if you always want to pull the image. You can also pull on demand if you want, eg. you need to use exampleImage:latest only when a new version is put up. So you can:

• 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!)