[YAML] 'log_level' is deprecated parameter name. use '@log_level' instead // parameter '$log_level' is not used

[ng-bsy]

Describe the bug

log_level on plugin scope can't be correctly defined in yaml config, without fluentd throwing a warning and/or the parameter not being recognized

To Reproduce

# Config 1
- match:
    $tag: '**'
    $type: stdout
    log_level: debug

results in:

[warn]: #0 'log_level' is deprecated parameter name. use '@log_level' instead.

since @ is not supported in yaml and every other instance of it has been replaced by $, looking at the fluentd documentation, I've also tried:

# Config 2
- match:
    $tag: '**'
    $type: stdout
    $log_level: debug

however this results in:

[warn]: parameter '$log_level' in <match **>
...
</match> is not used.

Expected behavior

I expect Config 2 not to throw a warning message and instead set the log_level at plugin scope to the according value.

Your Environment

- Fluentd version: 1.16.2
- TD Agent version:
- Operating system: Ubuntu 22.04 LTS
- Kernel version: 5.15

Your Configuration

see To Reproduce

Your Error Log

see To Reproduce

Additional context

No response

[daipom]

@ng-bsy Thanks for your report!
It seems that YAML format fails to take log_level setting into account.

• Handle YAML configuration format on configuration file #3712

We will check it.

[Shingo-Nakayama]

We have checked this report and it appears that YAML format doesn't support the $log_level.

We also confirmed that using log_level instead of $log_level results in warn messages, but the log_level setting works fine.

Although this may be improved by future modifications, you can use log_level (without $) for log_level setting for now.

[Shingo-Nakayama]

I add description for this issue in the official document.
https://docs.fluentd.org/configuration/config-file-yaml#special-yaml-elements