silence the 'log.SetLogger(...) was never called; logs will not be displayed' error

[zhzhuang-zju]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
Refer to #4868, when karmada-webhook is started, the error log.SetLogger(...) was never called; logs will not be displayed will be displayed, which is very confusing.
Here's the answer to why this log appears and how to fix it.
Viewing the function call chain, refer to:

karmada/vendor/sigs.k8s.io/controller-runtime/pkg/webhook/admission/webhook.go

Lines 178 to 184 in 95bf37f

	// getLogger constructs a logger from the injected log and LogConstructor.
	func (wh *Webhook) getLogger(req *Request) logr.Logger {
	wh.setupLogOnce.Do(func() {
	if wh.log.GetSink() == nil {
	wh.log = logf.Log.WithName("admission")
	}
	})

If the log of webhook is nil, it will end up calling

karmada/vendor/sigs.k8s.io/controller-runtime/pkg/log/log.go

Lines 54 to 72 in 95bf37f

	func eventuallyFulfillRoot() {
	if logFullfilled.Load() {
	return
	}
	if time.Since(rootLogCreated).Seconds() >= 30 {
	if logFullfilled.CompareAndSwap(false, true) {
	stack := debug.Stack()
	stackLines := bytes.Count(stack, []byte{'\n'})
	sep := []byte{'\n', '\t', '>', ' ', ' '}
	fmt.Fprintf(os.Stderr,
	"[controller-runtime] log.SetLogger(...) was never called; logs will not be displayed.\nDetected at:%s%s", sep,
	// prefix every line, so it's clear this is a stack trace related to the above message
	bytes.Replace(stack, []byte{'\n'}, sep, stackLines-1),
	)
	SetLogger(logr.New(NullLogSink{}))
	}
	}
	}

And the SetLogger is not called within the first 30 seconds of a binaries lifetime, finally printed out log.SetLogger(...) was never called; logs will not be displayed error.
Through the above analysis, there are two ways to solve this problem：

• Initializing the webhook's log
  Looking at the source code, there are two ways to initialize, in addition to the one above, there is one as follows:
  

  karmada/vendor/sigs.k8s.io/controller-runtime/pkg/webhook/admission/webhook.go

  Lines 216 to 233 in 95bf37f

  	// StandaloneWebhook prepares a webhook for use without a webhook.Server,
  	// passing in the information normally populated by webhook.Server
  	// and instrumenting the webhook with metrics.
  	//
  	// Use this to attach your webhook to an arbitrary HTTP server or mux.
  	//
  	// Note that you are responsible for terminating TLS if you use StandaloneWebhook
  	// in your own server/mux. In order to be accessed by a kubernetes cluster,
  	// all webhook servers require TLS.
  	func StandaloneWebhook(hook *Webhook, opts StandaloneOptions) (http.Handler, error) {
  	if opts.Logger.GetSink() != nil {
  	hook.log = opts.Logger
  	}
  	if opts.MetricsPath == "" {
  	return hook, nil
  	}
  	return metrics.InstrumentedHook(opts.MetricsPath, hook), nil
  	}

  
  Since this initialization method does not apply to webhook.Server, this method does not work

• call SetLogger to get any actual logging.
  That's what I ended up using, by calling SetLogger first to silence the 'log.SetLogger(...) was never called; logs will not be displayed' error.

BTW, it was a breaking change in the release notes 0.15.0 of controller-runtime. Previously, when the pkg/log package was imported, there was an init function that spawned a goroutine, which set a null logger after 30 seconds. Therefore, versions prior to 0.15.0 will not have this problem.

Which issue(s) this PR fixes:
Fixes #4868

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.06%. Comparing base (95bf37f) to head (f5de886).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4885      +/-   ##
==========================================
- Coverage   53.07%   53.06%   -0.01%     
==========================================
  Files         251      251              
  Lines       20389    20389              
==========================================
- Hits        10821    10820       -1     
  Misses       8855     8855              
- Partials      713      714       +1     

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[zhzhuang-zju]

cc @XiShanYongYe-Chang @whitewindmills @liangyuanpeng

[XiShanYongYe-Chang]

Thanks a lot!
/lgtm

[whitewindmills]

Does this problem exist other components?

[liangyuanpeng]

Thank you for your excellent analysis.

maybe we also need to update the webhook of example?
https://github.com/karmada-io/karmada/blob/master/examples/customresourceinterpreter/webhook/main.go

[zhzhuang-zju]

Does this problem exist other components?

Good advice. I'm lining it up.

[zhzhuang-zju]

Does this problem exist other components?

After troubleshooting, components karmada-controller-manager and karmada-metrics-adapter also have this problem. They both call the method

karmada/pkg/util/gclient/gclient.go

Lines 64 to 69 in 0e3c382

	// NewForConfig creates a new client for the given config.
	func NewForConfig(config *rest.Config) (client.Client, error) {
	return client.New(config, client.Options{
	Scheme: aggregatedScheme,
	})
	}

, which will eventually print log.SetLogger(...) was never called; logs will not be displayed error.
Component karmada-controller-manager only calls the above function if len(opts.ClusterAPIKubeconfig) !=0 , and that's why we don't usually find this error in component karmada-controller-manager !

[RainbowMango]

/approve

@whitewindmills @liangyuanpeng
Do you want to take another look?

Does this problem exist other components?

maybe we also need to update the webhook of example?

Excellent comments! By the way. Thanks.

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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[whitewindmills]

/lgtm