feat: create a KustomizeRenderer

The KustomizeRenderer is used to invoke Kustomize to the generated renderer.yaml.

plugins/scheduler-k3s/go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/dokku/dokku/plugins/logs v0.0.0-20250618161309-8d0c35f1333c
 	github.com/dokku/dokku/plugins/nginx-vhosts v0.0.0-20250618161309-8d0c35f1333c
 	github.com/fatih/color v1.18.0
+	github.com/fluxcd/pkg/kustomize v1.18.0
 	github.com/go-openapi/jsonpointer v0.21.1
 	github.com/go-resty/resty/v2 v2.16.5
 	github.com/gofrs/flock v0.12.1
@@ -30,6 +31,7 @@ require (
 	k8s.io/kubernetes v1.33.2
 	k8s.io/utils v0.0.0-20250604170112-4c0f3b243397
 	mvdan.cc/sh/v3 v3.12.0
+	sigs.k8s.io/kustomize/api v0.20.0
 )
 
 require (
@@ -168,7 +170,6 @@ require (
 	sigs.k8s.io/controller-runtime v0.21.0 // indirect
 	sigs.k8s.io/gateway-api v1.3.0 // indirect
 	sigs.k8s.io/json v0.0.0-20241014173422-cfa47c3a1cc8 // indirect
-	sigs.k8s.io/kustomize/api v0.20.0 // indirect
 	sigs.k8s.io/kustomize/kyaml v0.20.0 // indirect
 	sigs.k8s.io/randfill v1.0.0 // indirect
 	sigs.k8s.io/structured-merge-diff/v4 v4.7.0 // indirect

plugins/scheduler-k3s/go.sum

@@ -89,6 +89,8 @@ github.com/fatih/color v1.18.0 h1:S8gINlzdQ840/4pfAwic/ZE0djQEH3wM94VfqLTZcOM=
 github.com/fatih/color v1.18.0/go.mod h1:4FelSpRwEGDpQ12mAdzqdOukCy4u8WUtOY6lkT/6HfU=
 github.com/felixge/httpsnoop v1.0.4 h1:NFTV2Zj1bL4mc9sqWACXbQFVBBg2W3GPvqp8/ESS2Wg=
 github.com/felixge/httpsnoop v1.0.4/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
+github.com/fluxcd/pkg/kustomize v1.18.0 h1:wWK+qYwmBmba3N3VAqZ9ijnfVGGaIjcaHWo033URZTw=
+github.com/fluxcd/pkg/kustomize v1.18.0/go.mod h1:Ij9722MdWIE6B1EPg2ZJUf6npycgfRfN4Lohi7D/Kic=
 github.com/foxcpp/go-mockdns v1.1.0 h1:jI0rD8M0wuYAxL7r/ynTrCQQq0BVqfB99Vgk7DlmewI=
 github.com/foxcpp/go-mockdns v1.1.0/go.mod h1:IhLeSFGed3mJIAXPH2aiRQB+kqz7oqu8ld2qVbOu7Wk=
 github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=

plugins/scheduler-k3s/helm.go

@@ -14,6 +14,7 @@ import (
 	"unicode"
 
 	"github.com/dokku/dokku/plugins/common"
+	"github.com/fluxcd/pkg/kustomize/filesys"
 	"github.com/gofrs/flock"
 	"gopkg.in/yaml.v3"
 	"helm.sh/helm/v3/pkg/action"
@@ -21,9 +22,13 @@ import (
 	"helm.sh/helm/v3/pkg/cli"
 	"helm.sh/helm/v3/pkg/getter"
 	"helm.sh/helm/v3/pkg/kube"
+	"helm.sh/helm/v3/pkg/postrender"
 	"helm.sh/helm/v3/pkg/release"
 	"helm.sh/helm/v3/pkg/repo"
 	"helm.sh/helm/v3/pkg/storage/driver"
+	"sigs.k8s.io/kustomize/api/konfig"
+	"sigs.k8s.io/kustomize/api/krusty"
+	"sigs.k8s.io/kustomize/api/types"
 )
 
 var DevNullPrinter = func(format string, v ...interface{}) {}
@@ -337,16 +342,6 @@ func (h *HelmAgent) ListRevisions(input ListRevisionsInput) ([]Release, error) {
 	return releases, nil
 }
 
-type DebugRenderer struct {
-}
-
-func (p *DebugRenderer) Run(renderedManifests *bytes.Buffer) (*bytes.Buffer, error) {
-	for _, line := range strings.Split(renderedManifests.String(), "\n") {
-		common.LogWarn(line)
-	}
-	return renderedManifests, nil
-}
-
 func (h *HelmAgent) UpgradeChart(ctx context.Context, input ChartInput) error {
 	namespace := input.Namespace
 	if namespace == "" {
@@ -417,3 +412,77 @@ func (h *HelmAgent) UninstallChart(releaseName string) error {
 
 	return nil
 }
+
+type DebugRenderer struct {
+	Renderer *postrender.PostRenderer
+}
+
+func (p *DebugRenderer) Run(renderedManifests *bytes.Buffer) (*bytes.Buffer, error) {
+	if p.Renderer != nil {
+		var err error
+		renderer := *p.Renderer
+		renderedManifests, err = renderer.Run(renderedManifests)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	for _, line := range strings.Split(renderedManifests.String(), "\n") {
+		common.LogWarn(line)
+	}
+	return renderedManifests, nil
+}
+
+type KustomizeRenderer struct {
+	Renderer          *postrender.PostRenderer
+	KustomizeRootPath string
+}
+
+func (p *KustomizeRenderer) Run(renderedManifests *bytes.Buffer) (*bytes.Buffer, error) {
+	if p.KustomizeRootPath == "" {
+		return nil, nil
+	}
+
+	if !common.DirectoryExists(p.KustomizeRootPath) {
+		return nil, nil
+	}
+
+	fs, err := filesys.MakeFsOnDiskSecureBuild(p.KustomizeRootPath)
+	if err != nil {
+		return nil, fmt.Errorf("Error creating filesystem: %w", err)
+	}
+
+	var kfile string
+	for _, f := range konfig.RecognizedKustomizationFileNames() {
+		if kf := filepath.Join(p.KustomizeRootPath, f); fs.Exists(kf) {
+			kfile = kf
+			break
+		}
+	}
+	if kfile == "" {
+		return nil, fmt.Errorf("%s not found", konfig.DefaultKustomizationFileName())
+	}
+
+	renderedYamlPath := filepath.Join(p.KustomizeRootPath, "rendered.yaml")
+	if err := os.WriteFile(renderedYamlPath, renderedManifests.Bytes(), 0644); err != nil {
+		return nil, fmt.Errorf("Error writing rendered.yaml: %w", err)
+	}
+
+	buildOptions := &krusty.Options{
+		LoadRestrictions: types.LoadRestrictionsNone,
+		PluginConfig:     types.DisabledPluginConfig(),
+	}
+
+	k := krusty.MakeKustomizer(buildOptions)
+	m, err := k.Run(fs, p.KustomizeRootPath)
+	if err != nil {
+		return nil, err
+	}
+
+	resources, err := m.AsYaml()
+	if err != nil {
+		return nil, err
+	}
+
+	return bytes.NewBuffer(resources), nil
+}