Add file watcher for TLS certificate files

[afritzler]

Currently the agent and server are not honouring the change of TLS certificates provided to them. This PR introduces a file watcher for both agent and server to restart the corresponding components in case there as been a change in the TLS certificates.

Changes

• Add fsnotify dependency to go.mod
• Add file watcher for certificate files in cmd/agent/app/server.go and cmd/server/app/server.go
• Reload TLS config and credentials on certificate file change in cmd/agent/app/server.go and cmd/server/app/server.go
• Refactor and clean up file watcher code in cmd/agent/app/server.go and cmd/server/app/server.go

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[k8s-ci-robot]

Hi @afritzler. 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.

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[jkh52]

/ok-to-test

[jkh52]

Initial thoughts:

Some admins may want a security posture that disallows this, it could be better to opt-in to the new feature via flag (or at a minimum support an opt-out).

We need to make sure this doesn't make #350 harder to implement (seems like it shouldn't).

It would be nice to see some unit test coverage.

[jkh52]

/cc @tallclair

[afritzler]

@jkh52 thanks a lot for the feedback. Let me address the point of disabling the rotation + adding some test coverage.

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PR needs rebase.

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/lifecycle stale

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/lifecycle rotten

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/close

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@k8s-triage-robot: Closed this PR.

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/close

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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: afritzler / name: Andreas Fritzler (34f2fe7)

[jkh52]

@afritzler - see the effort at #577 (it would give you attribution, but 'EasyCLA check' does not pass. Can you fix that part?)

[k8s-ci-robot]

@afritzler: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-apiserver-network-proxy-docker-build-arm64-master	34f2fe7	link	true	/test pull-apiserver-network-proxy-docker-build-arm64-master
pull-apiserver-network-proxy-docker-build-amd64-master	34f2fe7	link	true	/test pull-apiserver-network-proxy-docker-build-amd64-master
pull-apiserver-network-proxy-make-lint-master	34f2fe7	link	true	/test pull-apiserver-network-proxy-make-lint-master
pull-apiserver-network-proxy-test-master	34f2fe7	link	true	/test pull-apiserver-network-proxy-test-master

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[afritzler]

@afritzler - see the effort at #577 (it would give you attribution, but 'EasyCLA check' does not pass. Can you fix that part?)

Thanks a lot for the update. I fixed the CLA issue. I guess we can close this PR in favor of #577.