Check if all images already exist, before pulling the images

[afbjorklund]

Is this a BUG REPORT or FEATURE REQUEST?

Choose one: FEATURE REQUEST

Versions

kubeadm version (use kubeadm version):

v1.32.0

Environment:

• Kubernetes version (use kubectl version): stable
• Cloud provider or hardware configuration: Lima
• OS (e.g. from /etc/os-release): Ubuntu LTS
• Kernel (e.g. uname -a): 6.8
• Container runtime (CRI) (e.g. containerd, cri-o): containerd
• Container networking plugin (CNI) (e.g. Calico, Cilium): flannel
• Others: QEMU/KVM

What happened?

When running the images preflight, the message is always printed:

[preflight] Pulling images required for setting up a Kubernetes cluster
[preflight] This might take a minute or two, depending on the speed of your internet connection
[preflight] You can also perform this action in beforehand using 'kubeadm config images pull'

What you expected to happen?

If you have already pulled all the images, a more friendly message:

[preflight] All images required for setting up a Kubernetes cluster exist

How to reproduce it (as minimally and precisely as possible)?

kubeadm init phase preflight

Anything else we need to know?

[SataQiu]

The existing images will be skipped. You can see the detailed info by kubeadm init phase preflight -v 1

# kubeadm init phase preflight -v 1
...
[preflight] Pulling images required for setting up a Kubernetes cluster
[preflight] This might take a minute or two, depending on the speed of your internet connection
[preflight] You can also perform this action in beforehand using 'kubeadm config images pull'
I0104 02:50:25.901834    3238 checks.go:828] using image pull policy: IfNotPresent
I0104 02:50:25.934956    3238 checks.go:846] image exists: registry.k8s.io/kube-apiserver:v1.28.15
I0104 02:50:25.969421    3238 checks.go:846] image exists: registry.k8s.io/kube-controller-manager:v1.28.15
I0104 02:50:26.004269    3238 checks.go:846] image exists: registry.k8s.io/kube-scheduler:v1.28.15
I0104 02:50:26.039219    3238 checks.go:846] image exists: registry.k8s.io/kube-proxy:v1.28.15
I0104 02:50:26.098499    3238 checks.go:846] image exists: registry.k8s.io/pause:3.9
I0104 02:50:26.125516    3238 checks.go:846] image exists: registry.k8s.io/etcd:3.5.9-0
I0104 02:50:26.152237    3238 checks.go:846] image exists: registry.k8s.io/coredns/coredns:v1.10.1
...

[neolit123]

So I already did the pull, and it is redundant.

1. "Pulling images required" : nothing left to pull
2. "This might take a minute or two": but not anymore
3. "You can also perform this action beforehand": already did

i gave the idea how it can be better implemented here
kubernetes/kubernetes#129474 (review)

but these few kubeadm lines are linear and not too output-poluting.
#3145 (comment)

Probably should stop the (unconfigured) kubelet service, while it is pulling the images?

combining the logs from multiple tools in the same output seems bad.
but yes, you can stop the kubelet before running kubeadm. kubeadm will start it again later.

there is a tracking issue to not start the kubelet with a crashloop until kubeadm prepares the config, but it also requires deb/rpm package updates, and maybe a KEP to polish all corner cases:

• change the kubelet service crash loop behavior #2178

[afbjorklund]

It could also be useful with a exist command, to see if the images have already been pulled...

Similar to the podman image exists command, which is missing from docker and containerd.

Currently doing a workaround:

images="$(kubeadm config images list)"; for image in $images; do sudo crictl image -q $image | grep -q sha256; done

Or a policy to pull, perhaps?

The airgapped tarballs should go in a separate issue, for now just using registry.k8s.io et al.

[pacoxu]

If you are sure that images already exist, you may try use ImagePullPolicy: Never like kubernetes/kubernetes#102901.

Similar to the podman image exists command, which is missing from docker and containerd.

Do you mean something like kubeadm config images exists to check if all images are ready?

[afbjorklund]

Do you mean something like kubeadm config images exists to check if all images are ready?

Yeah, I was using it to know if the kubeadm config images pull command had completed yet.

And if you issue another kubeadm config images pull, it will pull them from the network again.

I think it is "image exists" and "images exist", but then again I'm not a native speaker of English.