--logtostderr and --alsologtostderr flags no longer accepted in v0.6.0

[invidian]

What happened:

After updating metrics-server container image to v0.6.0, my deployment crashes with the following log:

panic: unknown flag: --logtostderr

goroutine 1 [running]:
main.main()
        /home/invidian/repos/metrics-server/cmd/metrics-server/metrics-server.go:39 +0xb9
exit status 2

What you expected to happen:

metrics-server to keep accepting previously working CLI flags, which are also defined in --help, like --logtostderr.

Anything else we need to know?:

Bisecting points to 8297c94.

/kind bug

[yangjunmyfm192085]

In my impression, this is the flag of klog, which should have been deleted in the latest version.
/cc @serathius
refer to:
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components

[serathius]

klog specific flags was deprecated in v1.23, K8s version that Metrics Server v0.6.0 bind it's dependencies. Removing those flags however was not intended, this happened due to changes in how flags are registered by component-base/logs package.

Overall I'm for removing klog flags, however only with proper previous communication. I think we should restore klog flags in v0.6.1 and announce their deprecation. Their removal should only happen in next release.

@dgrisonnet WDYT?

/triage accepted

[yangjunmyfm192085]

/assign

[dgrisonnet]

Your suggestion sounds good to me @serathius

[jcstanaway]

If we don't pass--logtostderr, where are logs sent to?

[invidian]

--logtostderr is true by default right now 😅 But I guess when it's false it goes to stdout? But this is not a question directly related to metrics-server, but more to klog.

[jcstanaway]

Took some digging, but found this comment buried in an example:

// By default klog writes to stderr. Setting logtostderr to false makes klog
// write to a log file.

https://github.com/kubernetes/klog/blob/main/examples/log_file/usage_log_file.go

[jcstanaway]

Also seeing v0.6.0 panic when passing --v:

[...]
  -v, --v Level                          number for the log level verbosity
      --vmodule moduleSpec               comma-separated list of pattern=N settings for file-filtered logging

panic: unknown flag: --v