External-ccm: Add node scoped reconciliation

[dghubble]

Summary

• Add a --node-filter-requirements Kubernetes label selector that restricts node-scoped reconciliation to matching Nodes
• Apply the selector to Kubernetes CCM controllers and OCI-specific Node informers while leaving non-Node resources unfiltered
• Preserve the existing all-Nodes behavior when the selector is empty
• Document the flag and selector syntax

Motivation

The OCI Cloud Controller Manager currently attempts to reconcile every Node in a cluster. This causes provider-specific operations to fail in hybrid clusters containing Nodes managed by other cloud providers. Node filtering lets operators define which Nodes the OCI CCM should manage.

Review fix

• Ensure generic InformerFor calls return the canonical filtered Node informer
• Add regression coverage for the order-sensitive shared informer cache bypass

Testing

• go test ./pkg/cloudprovider/providers/oci -run 'TestNewNodeFilteredSharedInformerFactory' -count=1
• go test ./pkg/cloudprovider/providers/oci -count=1

The CCM E2E suite was not run because a configured Kubernetes and OCI test cluster was not available.

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[l-technicore]

Thanks for adding node-scoped reconciliation.

Testing requested

Could you please include the following in the PR description?

• Manual test results, including the commands executed.
• If possible, results from the CCM E2E suite using FOCUS='[ccm]'.

This would provide additional confidence that the filtering change does not regress the external CCM controllers.

Filtering bypass found during review

We found a filtering bypass through the generic InformerFor path. Although Node requests were delegated to nodeFactory, the caller-provided constructor was passed through unchanged. Such a constructor can create an unfiltered Node informer because WithTweakListOptions is only captured by the generated typed constructor.

Since informers are cached by resource type, calling this path first can also cause typed callers to reuse the unfiltered cache.

Proposed fix

I opened dghubble/oci-cloud-controller-manager#1 with the fix and regression coverage. It ensures all Node InformerFor calls return the canonical filtered informer.

[GouthamML]

LGTM. will approve once the test results are shared and the aforementioned fix is in place

[dghubble]

I've incorporated the suggested change and regression coverage. Inquiring with my company and yours about how to satisfy the CLA.