Reload kube-state-metrics when kubeconfig changes.

[valayDave]

What would you like to be added:
The kube-state-metrics server takes the --kubeconfig argument. This argument allows passing a path to the kube-config file. When the kubeconfig file changes, the server doesn't automatically reload and we need to reload the server manually (or with hacky reload logic which we have to maintain downstream). If there were a way for the server to listen to a change in the kube-config file, then we wouldn't have to write any custom reload logic.

Why is this needed:
As good security measure, kubeconfig files should be short-lived and renewed periodically. Since kube-state-metrics takes a custom configuration file options, it would be really great if kube-state-metrics updates when the kube-config file changes.

Describe the solution you'd like
I have noticed that KSM already has a watcher for the --config file option (where it is trying to listen to the change in the file), Can a similar pattern be implemented for a --kubeconfig option ?

Additional context

[dashpole]

Might need change in k8s client go
/assign @dgrisonnet
/triage accepted

[dgrisonnet]

Sounds like something that could be beneficial to the project. I looked again in client-go and couldn't find any existing helper that we could reuse, so we will have to implement the watcher ourselves.

/help

[k8s-ci-robot]

@dgrisonnet:
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In response to this:

Sounds like something that could be beneficial to the project. I looked again in client-go and couldn't find any existing helper that we could reuse, so we will have to implement the watcher ourselves.

/help

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[opeco17]

I created PR (#2144) to implement the feature.
I'm using the same logic as the hot reload of --config .