Map --config flag in KubeletConfigSpec

[mdanielolsson]

Most config parameters passed as flags on the kubelet has been deprecated in favor of the --config parameter which expects a file as input. (https://kubernetes.io/docs/tasks/administer-cluster/kubelet-config-file/)

I read issue #5070 that the suggestion is to migrate away from the old style of migrating configuration to the kubelet, so I think this would be a good first step to just expose the flag. That way users can start migrating configuration to file before they are forced to do so.

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[johngmyers]

I don't see how exposing the flag is helpful. There would need to be code in kops for creating the config file that the flag points to and the settings exposed in the spec would need to be mapped to settings in that file instead of to flags.

[olemarkus]

The correct thing to do would be to parse our API to configfile params and compile the configfile. We already do this for some flags on KubeScheduler.

[johngmyers]

Converting our API struct to a KubeletConfiguration would be more complicated than the current code. Given the KubeletConfiguration format is beta, it would also increase our exposure to the risk of format changes.

[hakman]

We should probably move to KubeletConfiguration in 1.20. I doubt the format will change much. Maybe the API version from time to time, but we can handle it.

[hakman]

Closing, per the above comments.