Add support for RHEL 9 base images

[dsimansk]

/cc @Kaustubh-pande @rudyredhat1 @creydr

[Kaustubh-pande]

Maybe we can use just the safer side if we do a patch release 1.36.2 or newer

minor, _ := strconv.Atoi(strings.Split(metadata.Project.Version, ".")[1]) if minor <= 36 { rhelVersion = "rhel-8" } else { rhelVersion = "rhel-9" }

[creydr]

Thanks for checking on this @dsimansk
I left a few comments

[creydr]

Maybe we could also add the supposed RHEL version in the project.yaml file (maybe also easier for a potential RHEL 10 switch). In case the field would be empty (like in older SO versions), we could default to RHEL 8

[creydr]

Could also be helpful on parts like

hack/pkg/dockerfilegen/generator.go

Lines 439 to 447 in 051ce1f

	// use rhel suffix for OCP version >= 4.15
	soVersion := semver.New(metadata.Project.Version)
	rhelVersion, err := rhel.ForSOVersion(soVersion)
	if err != nil {
	return "", fmt.Errorf("could not determine rhel version: %v", err)
	}
	return fmt.Sprintf("oc.rhel%s", rhelVersion), nil

🙈

[dsimansk]

Indeed, it seemed quicker to hard code a few hacks in the current generator. But for the future and maintainability we should revisit it.

[dsimansk]

@Kaustubh-pande @creydr I've added disk free up commands to template and CI action. It should be good for review now.

[Kaustubh-pande]

/lgtm
/approve

[openshift-ci]

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[simkam]

with this I get error

serverless-operator$ make generated-files
GOFLAGS='' go install github.com/openshift-knative/hack/cmd/sobranch@latest
GOFLAGS='' go install -tags="exclude_graphdriver_btrfs containers_image_openpgp" github.com/containers/skopeo/cmd/skopeo@v1.17.0
GOFLAGS='' go install github.com/openshift-knative/hack/cmd/generate@latest
GOFLAGS='' go install github.com/openshift-knative/hack/cmd/sorhel@latest
GOFLAGS='' go install github.com/sigstore/cosign/cmd/cosign@latest
GOFLAGS='' go install github.com/operator-framework/operator-registry/cmd/opm@v1.47.0
GOFLAGS='' go install oras.land/oras/cmd/oras@v1.2.0
GOFLAGS='' go install github.com/openshift-knative/hack/cmd/generate@latest
/home/msimka/go/bin/generate \
        --generators dockerfile \
        --includes knative-operator \
        --includes openshift-knative-operator \
        --includes serving/ingress \
        --includes serving/metadata-webhook \
        --project-file olm-catalog/serverless-operator/project.yaml \
        --output /tmp/serverless-operator-generator/
2025/10/07 16:51:44 Main package path: serving/metadata-webhook/cmd/webhook
2025/10/07 16:51:44 Main package path: knative-operator/cmd/knative-operator
2025/10/07 16:51:44 Main package path: openshift-knative-operator/cmd/openshift-knative-operator
2025/10/07 16:51:44 Main package path: serving/ingress/cmd/ingress
2025/10/07 16:51:44 Dockerfile written: /tmp/serverless-operator-generator/ci-operator/build-image/Dockerfile
2025/10/07 16:51:44 Dockerfile written: /tmp/serverless-operator-generator/ci-operator/source-image/Dockerfile
2025/10/07 16:51:44 🔥 Error: bad template: Parsing failed: template: pattern matches no files: `dockerfile-templates/rhel-9/*.tmpl`

 - bad template

 - template: pattern matches no files: `dockerfile-templates/rhel-9/*.tmpl`
github.com/openshift-knative/hack/pkg/dockerfilegen.generateDockerfile
        /home/msimka/go/pkg/mod/github.com/openshift-knative/hack@v0.0.0-20251007121522-3642031d1093/pkg/dockerfilegen/generator.go:303
github.com/openshift-knative/hack/pkg/dockerfilegen.GenerateDockerfiles
        /home/msimka/go/pkg/mod/github.com/openshift-knative/hack@v0.0.0-20251007121522-3642031d1093/pkg/dockerfilegen/generator.go:137
main.GenerateMain
        /home/msimka/go/pkg/mod/github.com/openshift-knative/hack@v0.0.0-20251007121522-3642031d1093/cmd/generate/generate.go:33
main.main
        /home/msimka/go/pkg/mod/github.com/openshift-knative/hack@v0.0.0-20251007121522-3642031d1093/cmd/generate/generate.go:13
runtime.main
        /usr/lib/go-1.24/src/runtime/proc.go:283
runtime.goexit
        /usr/lib/go-1.24/src/runtime/asm_amd64.s:1700
make: *** [Makefile:345: generate-dockerfiles] Error 1

I'm golang newbie but shouldn't rhel-9 templates be embedded in https://github.com/openshift-knative/hack/blob/main/pkg/dockerfilegen/templates.go ?