Adds a log warning when falling back to default fake cert

[vncntvandriessche]

What this PR does / why we need it:
Adds a warning to the controller's log messages if a custom default certificate was passed but the controller falls back for #reason (err)

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #3278

Special notes for your reviewer:

[aledbf]

err is nil here

[aledbf]

Also, please use "Error loading...."

[vncntvandriessche]

😅 Fixed!

[aledbf]

@vncntvandriessche please change the code to something like

    // read custom default SSL certificate, fall back to generated default certificate
    if n.cfg.DefaultSSLCertificate != ""{
        defaultCertificate, err := n.store.GetLocalSSLCert(n.cfg.DefaultSSLCertificate)
        if err == nil {
            defaultPemFileName = defaultCertificate.PemFileName
            defaultPemSHA = defaultCertificate.PemSHA
        } else {
            klog.Warningf("Error loading custom default certificate, falling back to generated default:\n%v", err)
        }
    }

or the warning will flood the log

[vncntvandriessche]

@aledbf I applied the changes as you suggested: 1 thing scares me:

defaultCertificate, err := n.store.GetLocalSSLCert(n.cfg.DefaultSSLCertificate)

before my change that was an action that always happened, but would fail due to the value of n.cfg.DefaultSSLCertificate being an empty string.

I'm wondering if it would be more future-proof to write it like so:

[...]
// original block
	if err == nil {
		defaultPemFileName = defaultCertificate.PemFileName
		defaultPemSHA = defaultCertificate.PemSHA
	}

// Addition
	if err != nil && n.cfg.DefaultSSLCertificate != "" {
		klog.Warningf("Error loading custom default certificate, falling back to generated default:\n%v", err)
	}
[...]

TL;DR: Just add the if-block at "Addition" under the original code instead of adding the else.

[aledbf]

before my change that was an action that always happened, but would fail due to the value of n.cfg.DefaultSSLCertificate being an empty string.

The current code is fine. We should have a check for n.cfg.DefaultSSLCertificate not being empty in the previous version.

[vncntvandriessche]

Alright! Thanks for the guidance.

[aledbf]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, vncntvandriessche

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