feat(crd): Support MX record with trailing dot

[HartmannVolker]

What does it do ?

This PR allows trailing dots in MX Record targets, allowing to use a different FQDN for your Mail server

Motivation

Currently trailing dots are not supported in MX records that are created using the DNSEndpoint CRD. But an MX record with a trailing dot signifies a FQDN, instructing the DNS server not to append the root domain to the entry, which is important in case your Mail server is not running under the same domain.

Currently external DNS throughs a warning like this if the target has a trailing dot:

Endpoint <endpoint name> with DNSName fqdn.example.com. has an illegal target format.

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

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• ✅ login: HartmannVolker / name: Volker Hartmann (f6cd8c1)

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[ivankatliarchuk]

Missing before and after evidences/how-to-reproduce , so not clear how to reproduce and validate. Example expected #5085 (comment)

Missing documentation about MX record trailing dots requirement. Could be a breaking change, so the risk modifying this no clear.

[ivankatliarchuk]

can we have test without trailing dot as well

[ivankatliarchuk]

nesting if is not a great idea

consider something like

for _, target := range ep.Targets {
	hasDot := strings.HasSuffix(target, ".")

	// TXT can contain arbitrary text, skip dot validation.
	if isTXT {
		continue
	}

	// Records that require a trailing dot (hostnames).
	requiresDot := isNAPTR || isMx

	if requiresDot && !hasDot {
		illegalTarget = true
		break
	}

	if !requiresDot && hasDot {
		illegalTarget = true
		break
	}
}

[ivankatliarchuk]

Or we could avoid growing list of boolean variables entiretly

illegalTarget := false
for _, target := range ep.Targets {
	hasDot := strings.HasSuffix(target, ".")

	switch ep.RecordType {
	case endpoint.RecordTypeTXT:
		 continue // TXT records allow arbitrary text, skip validation
	case endpoint.RecordTypeNAPTR, endpoint.RecordTypeMX:
		illegalTarget = !hasDot // Must have trailing dot
	default:
		illegalTarget = hasDot // Must NOT have trailing dot
	}

	if illegalTarget {
		break
	}
}

[ivankatliarchuk]

/ok-to-test

[coveralls]

Pull Request Test Coverage Report for Build 21622765263

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.003%) to 79.161%

---

Files with Coverage Reduction	New Missed Lines	%
openshift_route.go	1	83.97%
crd.go	2	68.1%

Totals
Change from base Build 21559764040:	0.003%
Covered Lines:	16046
Relevant Lines:	20270

---

💛 - Coveralls

[ivankatliarchuk]

MX target could have trailing dot, but is not mandatory. Most likely both cases are valid