Add an option to diff with a local kustomization file

If implemented, users will be able to provide a local kustomization file
to `flux build/diff`.

Signed-off-by: Soule BA <soule@weave.works>

cmd/flux/build_kustomization.go

@@ -33,21 +33,28 @@ var buildKsCmd = &cobra.Command{
 	Short:   "Build Kustomization",
 	Long: `The build command queries the Kubernetes API and fetches the specified Flux Kustomization. 
 It then uses the fetched in cluster flux kustomization to perform needed transformation on the local kustomization.yaml
-pointed at by --path. The local kustomization.yaml is generated if it does not exist. Finally it builds the overlays using the local kustomization.yaml, and write the resulting multi-doc YAML to stdout.`,
+pointed at by --path. The local kustomization.yaml is generated if it does not exist. Finally it builds the overlays using the local kustomization.yaml, and write the resulting multi-doc YAML to stdout.
+
+It is possible to specify a Flux kustomization file using --kustomization-file.`,
 	Example: `# Build the local manifests as they were built on the cluster
-flux build kustomization my-app --path ./path/to/local/manifests`,
+flux build kustomization my-app --path ./path/to/local/manifests
+
+# Build using a local flux kustomization file
+flux build kustomization my-app --path ./path/to/local/manifests --kustomization-file ./path/to/local/my-app.yaml`,
 	ValidArgsFunction: resourceNamesCompletionFunc(kustomizev1.GroupVersion.WithKind(kustomizev1.KustomizationKind)),
 	RunE:              buildKsCmdRun,
 }
 
 type buildKsFlags struct {
-	path string
+	kustomizationFile string
+	path              string
 }
 
 var buildKsArgs buildKsFlags
 
 func init() {
-	buildKsCmd.Flags().StringVar(&buildKsArgs.path, "path", "", "Path to the manifests location.)")
+	buildKsCmd.Flags().StringVar(&buildKsArgs.path, "path", "", "Path to the manifests location.")
+	buildKsCmd.Flags().StringVar(&buildKsArgs.kustomizationFile, "kustomization-file", "", "Path to the Flux Kustomization YAML file.")
 	buildCmd.AddCommand(buildKsCmd)
 }
 
@@ -65,7 +72,13 @@ func buildKsCmdRun(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("invalid resource path %q", buildKsArgs.path)
 	}
 
-	builder, err := build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, buildKsArgs.path, build.WithTimeout(rootArgs.timeout))
+	if buildKsArgs.kustomizationFile != "" {
+		if fs, err := os.Stat(buildKsArgs.kustomizationFile); os.IsNotExist(err) || fs.IsDir() {
+			return fmt.Errorf("invalid kustomization file %q", buildKsArgs.kustomizationFile)
+		}
+	}
+
+	builder, err := build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, buildKsArgs.path, build.WithTimeout(rootArgs.timeout), build.WithKustomizationFile(buildKsArgs.kustomizationFile))
 	if err != nil {
 		return err
 	}

cmd/flux/build_kustomization_test.go

@@ -20,7 +20,10 @@ limitations under the License.
 package main
 
 import (
+	"bytes"
+	"os"
 	"testing"
+	"text/template"
 )
 
 func setup(t *testing.T, tmpl map[string]string) {
@@ -55,7 +58,7 @@ func TestBuildKustomization(t *testing.T) {
 			assertFunc: "assertGoldenTemplateFile",
 		},
 		{
-			name:       "build deployment and configmpa with var substitution",
+			name:       "build deployment and configmap with var substitution",
 			args:       "build kustomization podinfo --path ./testdata/build-kustomization/var-substitution",
 			resultFile: "./testdata/build-kustomization/podinfo-with-var-substitution-result.yaml",
 			assertFunc: "assertGoldenTemplateFile",
@@ -87,3 +90,101 @@ func TestBuildKustomization(t *testing.T) {
 		})
 	}
 }
+
+func TestBuildLocalKustomization(t *testing.T) {
+	podinfo := `apiVersion: kustomize.toolkit.fluxcd.io/v1beta2
+kind: Kustomization
+metadata:
+  name: podinfo
+  namespace: {{ .fluxns }}
+spec:
+  interval: 5m0s
+  path: ./kustomize
+  force: true
+  prune: true
+  sourceRef:
+    kind: GitRepository
+    name: podinfo
+  targetNamespace: default
+  postBuild:
+    substitute:
+      cluster_env: "prod"
+      cluster_region: "eu-central-1"
+`
+
+	tests := []struct {
+		name       string
+		args       string
+		resultFile string
+		assertFunc string
+	}{
+		{
+			name:       "no args",
+			args:       "build kustomization podinfo --kustomization-file ./wrongfile/ --path ./testdata/build-kustomization/podinfo",
+			resultFile: "invalid kustomization file \"./wrongfile/\"",
+			assertFunc: "assertError",
+		},
+		{
+			name:       "build podinfo",
+			args:       "build kustomization podinfo --kustomization-file ./testdata/build-kustomization/podinfo.yaml --path ./testdata/build-kustomization/podinfo",
+			resultFile: "./testdata/build-kustomization/podinfo-result.yaml",
+			assertFunc: "assertGoldenTemplateFile",
+		},
+		{
+			name:       "build podinfo without service",
+			args:       "build kustomization podinfo --kustomization-file ./testdata/build-kustomization/podinfo.yaml --path ./testdata/build-kustomization/delete-service",
+			resultFile: "./testdata/build-kustomization/podinfo-without-service-result.yaml",
+			assertFunc: "assertGoldenTemplateFile",
+		},
+		{
+			name:       "build deployment and configmap with var substitution",
+			args:       "build kustomization podinfo --kustomization-file ./testdata/build-kustomization/podinfo.yaml --path ./testdata/build-kustomization/var-substitution",
+			resultFile: "./testdata/build-kustomization/podinfo-with-var-substitution-result.yaml",
+			assertFunc: "assertGoldenTemplateFile",
+		},
+	}
+
+	tmpl := map[string]string{
+		"fluxns": allocateNamespace("flux-system"),
+	}
+
+	testEnv.CreateObjectFile("./testdata/build-kustomization/podinfo-source.yaml", tmpl, t)
+
+	temp, err := template.New("podinfo").Parse(podinfo)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var b bytes.Buffer
+	err = temp.Execute(&b, tmpl)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = os.WriteFile("./testdata/build-kustomization/podinfo.yaml", b.Bytes(), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.Remove("./testdata/build-kustomization/podinfo.yaml")
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var assert assertFunc
+
+			switch tt.assertFunc {
+			case "assertGoldenTemplateFile":
+				assert = assertGoldenTemplateFile(tt.resultFile, tmpl)
+			case "assertError":
+				assert = assertError(tt.resultFile)
+			}
+
+			cmd := cmdTestCase{
+				args:   tt.args + " -n " + tmpl["fluxns"],
+				assert: assert,
+			}
+
+			cmd.runTestCmd(t)
+		})
+	}
+}

cmd/flux/diff_kustomization.go

@@ -34,21 +34,26 @@ var diffKsCmd = &cobra.Command{
 	Long: `The diff command does a build, then it performs a server-side dry-run and prints the diff.
 Exit status: 0 No differences were found. 1 Differences were found. >1 diff failed with an error.`,
 	Example: `# Preview local changes as they were applied on the cluster
-flux diff kustomization my-app --path ./path/to/local/manifests`,
+flux diff kustomization my-app --path ./path/to/local/manifests
+
+# Preview using a local flux kustomization file
+flux diff kustomization my-app --path ./path/to/local/manifests --kustomization-file ./path/to/local/my-app.yaml`,
 	ValidArgsFunction: resourceNamesCompletionFunc(kustomizev1.GroupVersion.WithKind(kustomizev1.KustomizationKind)),
 	RunE:              diffKsCmdRun,
 }
 
 type diffKsFlags struct {
-	path        string
-	progressBar bool
+	kustomizationFile string
+	path              string
+	progressBar       bool
 }
 
 var diffKsArgs diffKsFlags
 
 func init() {
-	diffKsCmd.Flags().StringVar(&diffKsArgs.path, "path", "", "Path to a local directory that matches the specified Kustomization.spec.path.)")
+	diffKsCmd.Flags().StringVar(&diffKsArgs.path, "path", "", "Path to a local directory that matches the specified Kustomization.spec.path.")
 	diffKsCmd.Flags().BoolVar(&diffKsArgs.progressBar, "progress-bar", true, "Boolean to set the progress bar. The default value is true.")
+	diffKsCmd.Flags().StringVar(&diffKsArgs.kustomizationFile, "kustomization-file", "", "Path to the Flux Kustomization YAML file.")
 	diffCmd.AddCommand(diffKsCmd)
 }
 
@@ -66,12 +71,18 @@ func diffKsCmdRun(cmd *cobra.Command, args []string) error {
 		return &RequestError{StatusCode: 2, Err: fmt.Errorf("invalid resource path %q", diffKsArgs.path)}
 	}
 
+	if diffKsArgs.kustomizationFile != "" {
+		if fs, err := os.Stat(diffKsArgs.kustomizationFile); os.IsNotExist(err) || fs.IsDir() {
+			return fmt.Errorf("invalid kustomization file %q", diffKsArgs.kustomizationFile)
+		}
+	}
+
 	var builder *build.Builder
 	var err error
 	if diffKsArgs.progressBar {
-		builder, err = build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, diffKsArgs.path, build.WithTimeout(rootArgs.timeout), build.WithProgressBar())
+		builder, err = build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, diffKsArgs.path, build.WithTimeout(rootArgs.timeout), build.WithKustomizationFile(diffKsArgs.kustomizationFile), build.WithProgressBar())
 	} else {
-		builder, err = build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, diffKsArgs.path, build.WithTimeout(rootArgs.timeout))
+		builder, err = build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, diffKsArgs.path, build.WithTimeout(rootArgs.timeout), build.WithKustomizationFile(diffKsArgs.kustomizationFile))
 	}
 
 	if err != nil {

internal/build/build.go

@@ -22,6 +22,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"os"
 	"sync"
 	"time"
 
@@ -30,6 +31,7 @@ import (
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
+	k8syaml "k8s.io/apimachinery/pkg/util/yaml"
 	"k8s.io/cli-runtime/pkg/genericclioptions"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 	"sigs.k8s.io/kustomize/api/resmap"
@@ -60,11 +62,12 @@ var defaultTimeout = 80 * time.Second
 // It retrieves the kustomization object from the k8s cluster
 // and overlays the manifests with the resources specified in the resourcesPath
 type Builder struct {
-	client        client.WithWatch
-	restMapper    meta.RESTMapper
-	name          string
-	namespace     string
-	resourcesPath string
+	client            client.WithWatch
+	restMapper        meta.RESTMapper
+	name              string
+	namespace         string
+	resourcesPath     string
+	kustomizationFile string
 	// mu is used to synchronize access to the kustomization file
 	mu            sync.Mutex
 	action        kustomize.Action
@@ -75,6 +78,13 @@ type Builder struct {
 
 type BuilderOptionFunc func(b *Builder) error
 
+func WithKustomizationFile(file string) BuilderOptionFunc {
+	return func(b *Builder) error {
+		b.kustomizationFile = file
+		return nil
+	}
+}
+
 func WithTimeout(timeout time.Duration) BuilderOptionFunc {
 	return func(b *Builder) error {
 		b.timeout = timeout
@@ -176,9 +186,18 @@ func (b *Builder) build() (m resmap.ResMap, err error) {
 	defer cancel()
 
 	// Get the kustomization object
-	k, err := b.getKustomization(ctx)
-	if err != nil {
-		return
+	k := &kustomizev1.Kustomization{}
+	if b.kustomizationFile != "" {
+		k, err = b.unMarshallKustomization()
+		if err != nil {
+			return
+		}
+	} else {
+		k, err = b.getKustomization(ctx)
+		if err != nil {
+			err = fmt.Errorf("failed to get kustomization object: %w", err)
+			return
+		}
 	}
 
 	// store the kustomization object
@@ -225,6 +244,21 @@ func (b *Builder) build() (m resmap.ResMap, err error) {
 
 }
 
+func (b *Builder) unMarshallKustomization() (*kustomizev1.Kustomization, error) {
+	data, err := os.ReadFile(b.kustomizationFile)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read kustomization file %s: %w", b.kustomizationFile, err)
+	}
+
+	k := &kustomizev1.Kustomization{}
+	decoder := k8syaml.NewYAMLOrJSONDecoder(bytes.NewBuffer(data), len(data))
+	err = decoder.Decode(k)
+	if err != nil {
+		return nil, fmt.Errorf("failed to unmarshall kustomization file %s: %w", b.kustomizationFile, err)
+	}
+	return k, nil
+}
+
 func (b *Builder) generate(kustomization kustomizev1.Kustomization, dirPath string) (kustomize.Action, error) {
 	data, err := runtime.DefaultUnstructuredConverter.ToUnstructured(&kustomization)
 	if err != nil {