feat: Add DNS patch

[jimmidyson]

Depends on #129.

[github-actions]

This PR/issue depends on:

• feat: Add API server cert SANs patch #129
  By Dependent Issues (🤖). Happy coding!

[jimmidyson]

@dkoshkin do we really need to be able to override DNS image repo here? Is it not enough to just be able to override the registry images come from at kubeadmconfig top level that applies to all images?

[dkoshkin]

@dkoshkin do we really need to be able to override DNS image repo here? Is it not enough to just be able to override the registry images come from at kubeadmconfig top level that applies to all images?

I had the same thought for this repo @jimmidyson and why I asked if it was somehow related to API SANs. DKP has a very specific usecase because of how FIPS support works, but for a more generic solution I think having a variable for the registry is more valuable.

[jimmidyson]

For the fips case do we really need to override the DNS registry via "/spec/template/spec/kubeadmConfigSpec/clusterConfiguration/dns/imageRepository" or is it enough to be able just to override "/spec/template/spec/kubeadmConfigSpec/clusterConfiguration/imageRepository" (https://github.com/kubernetes-sigs/cluster-api/blob/82eff49867008365d3b26f82b55ff29a67880aa7/bootstrap/kubeadm/api/v1beta1/kubeadm_types.go#L139)? Why do we need to override the individual component image repositories (which really should be image registry iiuc...)?

[jimmidyson]

We could also just solve that with inline patches on fips cluster classes perhaps in addition to generic external patches 🤔

[jimmidyson]

Ah I see the note that coredns should always be pulled from default k8s registry

[jimmidyson]

Closing - as discussed above this does not appear to be a common enough use case to provide a patch for. This can be handled via inline patches, or a different patch webhook deployment.