filter_kubernetes: Add ability to change kubelet_host

[tumd]

Allow the user to set kubelet_host when use_kubelet is true.
Defaults to '127.0.0.1'.

Fixes #5143

Signed-off-by: Thomas Danielsson thomas.danielsson@sharespine.com

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change

[INPUT]
  Name dummy
  Dummy {"top": {".dotted": "value"}}

[FILTER]
  Name          kubernetes
  Match         *
  Use_Kubelet   true
  Kubelet_Host  ${KUBELET_HOST}
  Kubelet_Port  10250


[OUTPUT]
  Name stdout
  Match *

• Debug log output from testing the change

[2022/04/12 10:12:30] [ info] [filter:kubernetes:kubernetes.0] https=1 host=10.132.15.210 port=10250
[2022/04/12 10:12:30] [ info] [filter:kubernetes:kubernetes.0] local POD info OK
[2022/04/12 10:12:30] [ info] [filter:kubernetes:kubernetes.0] testing connectivity with Kubelet...
[2022/04/12 10:12:30] [debug] [filter:kubernetes:kubernetes.0] Send out request to Kubelet for pods information.
[2022/04/12 10:12:30] [debug] [http_client] not using http_proxy for header
[2022/04/12 10:12:30] [debug] [http_client] server 10.132.15.210:10250 will close connection #67
[2022/04/12 10:12:30] [debug] [filter:kubernetes:kubernetes.0] Request (ns=logging, pod=fluent-bit-kt7hc) http_do=0, HTTP Status: 200
[2022/04/12 10:12:30] [ info] [filter:kubernetes:kubernetes.0] connectivity OK

• [N/A] Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A] Attached local packaging test output showing all targets (including any new ones) build.

Documentation

• Documentation required for this feature
  pipeline: filters: kubernetes: Add kubelet_host fluent-bit-docs#787

Backporting

• [N/A] Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[patrick-stephens]

Can you rebase as seems to be picking up a fixed error in linting?

[tumd]

@patrick-stephens Done!

[wmedlar]

This is a very valuable addition for secure environments. Can we get the ball rolling on review again?

cc codeowners: @edsiper @leonardo-albertovich @fujimotos @koleini

[leonardo-albertovich]

I don't know nearly enough about kubernetes to understand the rational of this but the code changes look harmless since the default behavior is retained through the default value in the configuration entry.

I'd say it's good as long as the tests pass.