cmd/kubelet: implement drop-in configuration directory for kubelet

[sohankunkerkar]

This implements a drop-in configuration directory for the kubelet by introducing a --config-dir flag. Users can provide individual kubelet config snippets in separate files, formatted similarly to kubelet.conf. The kubelet will process the files in alphanumeric order, appending configurations if subfield(s) doesn't exist, overwriting them if they do, and handling lists by overwriting instead of merging.

What type of PR is this?

/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Implement alpha support for a drop-in kubelet configuration directory

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[KEP-3983](https://github.com/kubernetes/enhancements/blob/master/keps/sig-node/3983-drop-in-configuration/README.md)

[k8s-ci-robot]

Hi @sohankunkerkar. Thanks for your PR.

I'm waiting for a kubernetes 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.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[mrunalp]

/ok-to-test

[ffromani]

/triage accepted
/prioritiy important-soon

[haircommander]

Jul 18 21:34:31.374899 e2e-f9c33b17b2-674b9-master kubelet[10183]: E0718 21:34:31.374829   10183 run.go:74] "command failed" err="flag  specified but environment variable KUBELET_CONFIG_DROPIN_DIR_ALPHA not set, cannot start kubelet"

I think we should set the default value to "" to start. WDYT @SergeyKanzhelev @mrunalp @sohankunkerkar

[SergeyKanzhelev]

Jul 18 21:34:31.374899 e2e-f9c33b17b2-674b9-master kubelet[10183]: E0718 21:34:31.374829   10183 run.go:74] "command failed" err="flag  specified but environment variable KUBELET_CONFIG_DROPIN_DIR_ALPHA not set, cannot start kubelet"

I think we should set the default value to "" to start. WDYT @SergeyKanzhelev @mrunalp @sohankunkerkar

yes. Maybe even forever.

[mrunalp]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 9f0655af011a68bbab2775d8fb2d0d218ab10619

[haircommander]

/retest

[haircommander]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 570d2e55b1011fc4a0d502226aa6fb5f98f792f7

[k8s-ci-robot]

@sohankunkerkar: The following test 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-kubernetes-e2e-gce-cos-alpha-features	84fa31df501484f4dd742148ada1182eed02530a	link	false	/test pull-kubernetes-e2e-gce-cos-alpha-features

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.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[haircommander]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: c377fc4be14b67eb39618ccaf26eb76c4c8ffd7e