[2.17] fix imageRepository path for CoreDNS v1.8.0 #8182

[sebfere]

Thanks to the fix, I can now deploy the Kubernetes cluster as kubeadm can download the coredns image.
Resulting /etc/kubernetes/kubeadm-images.yaml:

apiVersion: kubeadm.k8s.io/v1beta2
kind: InitConfiguration
nodeRegistration:
  criSocket: /var/run/containerd/containerd.sock
---
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
imageRepository: k8s.gcr.io
kubernetesVersion: v1.21.6
etcd:
  local:
    imageRepository: "quay.io/coreos"
    imageTag: "v3.4.13"
dns:
  type: CoreDNS
  imageRepository: k8s.gcr.io/coredns
  imageTag: v1.8.0

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[sebfere]

CLA done.

[floryut]

I'll review this next week but I don't see why would this be needed as coredns 1.8.0 is set for a long time in master without any issue 🤔

[oomichi]

@MRoci Please take a look at this if possible.

[oomichi]

The above has been updated since #7570 for coredns versions <=1.7.0.
It would be safer to have some condition for switching the above for versions.

[oomichi]

/check-cla

[MRoci]

with kubernetes/kubernetes@38a41e1 and kubernetes release 1.21.2 kubeadm's constant CoreDNSImageName has been changed from coredns/coredns to coredns.

Because of that setting imageRepository to k8s.gcr.io/coredns to pull k8s.gcr.io/coredns/coredns:v1.8.0 makes sense to me, but from what i see this should be handled automatically by kubeadm itself and this change should not be necessary

[floryut]

Anyway, this won't be merged as long as it's not done in master prior to release branch
/hold

[kien-truong]

@MRoci

Because of that setting imageRepository to k8s.gcr.io/coredns to pull k8s.gcr.io/coredns/coredns:v1.8.0 makes sense to me, but from what i see this should be handled automatically by kubeadm itself and this change should not be necessary

It's in the commit you mentioned: kubeadm will only prepend the namespace automatically when using the default repository.
So k8s.gcr.io will be transformed into k8s.gcr.io/coredns, but abc.xyz will NOT be converted to abc.xyz/coredns.
If the user wants to use a custom repository like abc.xyz, then the generated kubeadm config file should say abc.xyz/coredns

@sebfere
Would you mind opening a pull request against master branch ? 2.18 is about to be released and should contain this fix.

[MRoci]

@kien-truong

It's in the commit you mentioned: kubeadm will only prepend the namespace automatically when using the default repository. So k8s.gcr.io will be transformed into k8s.gcr.io/coredns, but abc.xyz will NOT be converted to abc.xyz/coredns. If the user wants to use a custom repository like abc.xyz, then the generated kubeadm config file should say abc.xyz/coredns

for custom repositories for sure but as per #8182 this problem affects also users that have the default imageRepository setting (k8s.gcr.io) which should not be the case since it should be handled by kubeadm.

I think that it can be caused when trying to pull coredns:v1.8 with kubeadm<=1.20 which stil expects the old k8s.gcr.io./coredns:1.xx format and also by default ships coredns:v1.7

WIth this fix imageRepository will be set to k8s.gcr.io/coredns being unable to use CoreDNS versions previous than 1.7 and breaking with kubeadm 1.21.0 and 1.21.1 since they have hardcoded the image name as coredns/coredns

[kien-truong]

I think that it can be caused when trying to pull coredns:v1.8 with kubeadm<=1.20 which stil expects the old k8s.gcr.io./coredns:1.xx format and also by default ships coredns:v1.7

Doesn't Kupespray automatically update Kubeadm to the correct version of Kubeadm during deployment ?
Unless the users have a different kubeadm in PATH that shadow Kubespray's , in which case maybe Kubespray should give a warning.

WIth this fix imageRepository will be set to k8s.gcr.io/coredns being unable to use CoreDNS versions previous than 1.7 and breaking with kubeadm 1.21.0 and 1.21.1 since they have hardcoded the image name as coredns/coredns

CoreDNS <= 1.7 is already handled per the existing code, and I think Kubeadm 1.21.0 and 1.21.1 can be checked similarly.

coredns_image_is_namespaced: "{{ (kube_version is version('v1.21.0','>=')) or (coredns_version is version('v1.7.1','>=')) }}"
coredns_image_repo: "{{ kube_image_repo }}{{'/coredns/coredns' if (coredns_image_is_namespaced | bool) else '/coredns' }}"

[MRoci]

@kien-truong
given the fact that for newer versions of kubeadm and coredns it should work either if imageRepository is set to k8s.gcr.io or k8s.gcr.io/coredns maybe in order to use the default k8s.gcr.io, k8s.gcr.io/coredns can be set when kube_version<=1.20 and coredns>=1.8

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