fix:Add preflight guard against cluster identity changes on existing …

[isumitsolanki]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Adds a preflight validation in kubernetes/preinstall to prevent unsafe changes to cluster identity on existing clusters.

When Kubespray is re-run against an existing cluster, it now reads the current kubeadm config ({{ kube_config_dir }}/kubeadm-config.yaml) and compares:

• cluster_name (kubeadm clusterName)
• dns_domain (kubeadm networking.dnsDomain)

If either value differs from inventory, the playbook fails fast with a clear error. This avoids partial reconfiguration that can break certificates, service-account token issuer expectations, DNS, and CNI behavior.

Which issue(s) this PR fixes:

Fixes #13233

Special notes for your reviewer:

• The check is scoped to existing clusters only (when kubeadm config file exists).
• It runs once on the first control-plane host.
• It respects ignore_assert_errors, consistent with other preinstall assertions.
• Fresh installs are not affected.

Does this PR introduce a user-facing change?:

Kubespray now fails early if `cluster_name` or `dns_domain` is changed for an existing cluster. Changing these values in-place is unsupported and can cause cluster-wide disruption; users should keep the original values or redeploy a new cluster.

[k8s-ci-robot]

Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: isumitsolanki
Once this PR has been reviewed and has the lgtm label, please assign yankay for approval. For more information see the Code Review Process.

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[k8s-ci-robot]

Hi @isumitsolanki. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[yankay]

/ok-to-test