export swap behavior via label

[fmuyassarov]

This patch exports a label indicating the kubelet's configured swap behavior. By default, it reads from /var/lib/kubelet/config.yaml. If a custom kubelet config path is used, it can be set via the -kubelet-config-path flag.
If the swap behavior is not specified, NoSwap is assumed (matching kubelet's default).

Note: feature.node.kubernetes.io/memory-swap.behavior (or in general kubelet's memorySwap.swapBehavior) reflects whether k8s workloads are allowed to use swap. A node may have swap enabled, but if kubelet is set to NoSwap, pods cannot use it. As such, the behavior label will be exported only if node level swap is enabled.

      feature.node.kubernetes.io/memory-swap: "true"
      feature.node.kubernetes.io/memory-swap.behavior: LimitedSwap

Fixes: #2178

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: fmuyassarov
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[fmuyassarov]

@marquiz Do you have any suggestions for handling this part?
When a custom kubelet config path is used, I want to ensure the user-specified path (via the kubelet-config-path flag) is correctly propagated. There are two places where this path needs to be dynamic.

1. when mounting the path so the NFD worker can read the file
2. when passing the path to the worker (this part is already handled).
   The issue is that it's easy to parameterize this in Helm, but I haven't found a clean way to do it with Kustomize.

Also, for the Helm specifically, do you think it makes sense to place the flag under worker.config, or would another location be more appropriate?

[fmuyassarov]

/test pull-node-feature-discovery-build-image-cross-generic

[marquiz]

@fmuyassarov thank you for the patch and working on this. Let's get this finalized.

My main comment is that in topology-updater we already read the kubelet config (read from the kubelet configz endpoint by default), helpers are in pkg/utils/kubeconf/. Could we do the same on nfd-worker?

[fmuyassarov]

@fmuyassarov thank you for the patch and working on this. Let's get this finalized.

My main comment is that in topology-updater we already read the kubelet config (read from the kubelet configz endpoint by default), helpers are in pkg/utils/kubeconf/. Could we do the same on nfd-worker?

I will check that.