Set ingress class via ingressClassName for Contour HTTPProxy

[nnz1024]

Since version 1.18 (released in July 2021), Contour supports field HTTPProxy.spec.ingressClassName as a way to specify ingress class for HTTPProxy.

Using this field allows to avoid problems emerging from improper annotation cleanup, diffing and copying (see referenced issue).

Fixes: #1848

[aryan9600]

hello, thank you for raising this PR! it looks good at first glance. is it possible to still keep the annotation around?

[nnz1024]

Hello, @aryan9600!
First of all, thanks for your work to keep Flagger afloat!

Yes, we can keep this annotation. To prevent code duplication, we can use function like this

func setIngressClass(ingressClass string, annotations *map[string]string, proxySpec *contourv1.HTTPProxySpec) {
	if ingressClass == "" {
		return
	}

	if *annotations == nil {
		*annotations = make(map[string]string)
	}
	(*annotations)["projectcontour.io/ingress.class"] = ingressClass

	proxySpec.IngressClassName = ingressClass
}

like

setIngressClass(cr.ingressClass, &newMetadata.Annotations, &newSpec)

and

setIngressClass(cr.ingressClass, &proxy.Annotations, &proxy.Spec)

Already checked that it compiles, bit it will take several more days to thoroughly test it.

However, in my opinion, removing annotation modification would be beneficial. Looking at Flagger's commit history, one can see that more than half of the fixes in recent years relate to annotation diffing, filtering, and rewriting across different custom resources. Using the native resource field could reduce the potential for errors and make future maintenance of Flagger easier.

Another reason not to support this annotation is that latest version of Contour without native IngressClassName support was 1.17.2, released in Aug 2021 and tested for compatibility with Kubernetes versions up to 1.21. Since then, there have been many critical vulnerabilities in Go and Envoy, and today's oldest supported Kubernetes version is 1.32. So, I doubt there is a real chance to encounter such an old Contour.

In summary: while it is possible to keep the annotation, I believe it is better to minimize annotation interactions, especially since it is very unlikely that anyone in 2026 will need this specific annotation.

[aryan9600]

fair enough - could you rebase against main and force push?

[nnz1024]

Done

[nnz1024]

Sorry, forgot about tests

[nnz1024]

Hello @aryan9600!

Can you please re-trigger tests?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 30.00%. Comparing base (36a2088) to head (f19ee00).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/router/contour.go	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1870   +/-   ##
=======================================
  Coverage   30.00%   30.00%           
=======================================
  Files         287      287           
  Lines       18467    18468    +1     
=======================================
+ Hits         5541     5542    +1     
  Misses      12195    12195           
  Partials      731      731           

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[nnz1024]

OK, now with green tests I only have to rebase it on the main branch?