Add a dry-run mode to flux build kustomization

If implemented user will be able to use `flux build kustomization`
without any connection to the cluster.

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

cmd/flux/build_kustomization.go

@@ -40,25 +40,30 @@ It is possible to specify a Flux kustomization file using --kustomization-file.`
 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`,
+flux build kustomization my-app --path ./path/to/local/manifests --kustomization-file ./path/to/local/my-app.yaml
+
+# Build in dry-run mode, i.e. do not connect to the cluster at all
+flux build kustomization my-app --path ./path/to/local/manifests --kustomization-file ./path/to/local/my-app.yaml --dry-run`,
 	ValidArgsFunction: resourceNamesCompletionFunc(kustomizev1.GroupVersion.WithKind(kustomizev1.KustomizationKind)),
 	RunE:              buildKsCmdRun,
 }
 
 type buildKsFlags struct {
 	kustomizationFile string
 	path              string
+	dryRun            bool
 }
 
 var buildKsArgs buildKsFlags
 
 func init() {
 	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.")
+	buildKsCmd.Flags().BoolVar(&buildKsArgs.dryRun, "dry-run", false, "Dry run mode.")
 	buildCmd.AddCommand(buildKsCmd)
 }
 
-func buildKsCmdRun(cmd *cobra.Command, args []string) error {
+func buildKsCmdRun(cmd *cobra.Command, args []string) (err error) {
 	if len(args) < 1 {
 		return fmt.Errorf("%s name is required", kustomizationType.humanKind)
 	}
@@ -72,13 +77,22 @@ func buildKsCmdRun(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("invalid resource path %q", buildKsArgs.path)
 	}
 
+	if buildKsArgs.dryRun && buildKsArgs.kustomizationFile == "" {
+		return fmt.Errorf("dry-run mode requires a kustomization file")
+	}
+
 	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))
+	builder, err := build.NewBuilder(name, buildKsArgs.path,
+		build.WithClientConfig(kubeconfigArgs, kubeclientOptions),
+		build.WithTimeout(rootArgs.timeout),
+		build.WithKustomizationFile(buildKsArgs.kustomizationFile),
+		build.WithDryRun(buildKsArgs.dryRun),
+	)
 	if err != nil {
 		return err
 	}

cmd/flux/build_kustomization_test.go

@@ -142,6 +142,12 @@ spec:
 			resultFile: "./testdata/build-kustomization/podinfo-with-var-substitution-result.yaml",
 			assertFunc: "assertGoldenTemplateFile",
 		},
+		{
+			name:       "build deployment and configmap with var substitution in dry-run mode",
+			args:       "build kustomization podinfo --kustomization-file ./testdata/build-kustomization/podinfo.yaml --path ./testdata/build-kustomization/var-substitution --dry-run",
+			resultFile: "./testdata/build-kustomization/podinfo-with-var-substitution-result.yaml",
+			assertFunc: "assertGoldenTemplateFile",
+		},
 	}
 
 	tmpl := map[string]string{

cmd/flux/diff_kustomization.go

@@ -77,12 +77,21 @@ func diffKsCmdRun(cmd *cobra.Command, args []string) error {
 		}
 	}
 
-	var builder *build.Builder
-	var err error
+	var (
+		builder *build.Builder
+		err     error
+	)
 	if diffKsArgs.progressBar {
-		builder, err = build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, diffKsArgs.path, build.WithTimeout(rootArgs.timeout), build.WithKustomizationFile(diffKsArgs.kustomizationFile), build.WithProgressBar())
+		builder, err = build.NewBuilder(name, diffKsArgs.path,
+			build.WithClientConfig(kubeconfigArgs, kubeclientOptions),
+			build.WithTimeout(rootArgs.timeout),
+			build.WithKustomizationFile(diffKsArgs.kustomizationFile),
+			build.WithProgressBar())
 	} else {
-		builder, err = build.NewBuilder(kubeconfigArgs, kubeclientOptions, name, diffKsArgs.path, build.WithTimeout(rootArgs.timeout), build.WithKustomizationFile(diffKsArgs.kustomizationFile))
+		builder, err = build.NewBuilder(name, diffKsArgs.path,
+			build.WithClientConfig(kubeconfigArgs, kubeclientOptions),
+			build.WithTimeout(rootArgs.timeout),
+			build.WithKustomizationFile(diffKsArgs.kustomizationFile))
 	}
 
 	if err != nil {

cmd/flux/diff_kustomization_test.go

@@ -97,7 +97,7 @@ func TestDiffKustomization(t *testing.T) {
 		"fluxns": allocateNamespace("flux-system"),
 	}
 
-	b, _ := build.NewBuilder(kubeconfigArgs, kubeclientOptions, "podinfo", "")
+	b, _ := build.NewBuilder("podinfo", "", build.WithClientConfig(kubeconfigArgs, kubeclientOptions))
 
 	resourceManager, err := b.Manager()
 	if err != nil {

go.mod

@@ -2,7 +2,7 @@ module github.com/fluxcd/flux2
 
 go 1.18
 
-replace github.com/fluxcd/pkg/kustomize => github.com/souleb/pkg/kustomize v0.0.0-20221114164450-c3ad651f477b
+replace github.com/fluxcd/pkg/kustomize => github.com/souleb/pkg/kustomize v0.0.0-20221115105652-bfcd8988ecc8
 
 require (
 	github.com/Masterminds/semver/v3 v3.1.1

go.sum

@@ -592,8 +592,8 @@ github.com/sirupsen/logrus v1.6.0/go.mod h1:7uNnSEd1DgxDLC74fIahvMZmmYsHGZGEOFrf
 github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
 github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
 github.com/sirupsen/logrus v1.9.0/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
-github.com/souleb/pkg/kustomize v0.0.0-20221114164450-c3ad651f477b h1:JlaF96cEGlAxdW7NYi8ON398wR2xtrJkRUAAHFCTh0w=
-github.com/souleb/pkg/kustomize v0.0.0-20221114164450-c3ad651f477b/go.mod h1:rXQcYjvqqS+9oCOA2J/w7KTnwNhdwDCeW4mE5zQRjN4=
+github.com/souleb/pkg/kustomize v0.0.0-20221115105652-bfcd8988ecc8 h1:8ffW88dnCuwYL3zZRkFfxM4OCM3kfT4a2fzMH4HQDWY=
+github.com/souleb/pkg/kustomize v0.0.0-20221115105652-bfcd8988ecc8/go.mod h1:rXQcYjvqqS+9oCOA2J/w7KTnwNhdwDCeW4mE5zQRjN4=
 github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=
 github.com/spf13/afero v1.2.2/go.mod h1:9ZxEEn6pIJ8Rxe320qSDBk6AsU0r9pR7Q4OcevTdifk=
 github.com/spf13/cobra v1.6.0 h1:42a0n6jwCot1pUmomAp4T7DeMD+20LFv4Q54pxLf2LI=

internal/build/build.go

@@ -76,17 +76,21 @@ type Builder struct {
 	kustomization *kustomizev1.Kustomization
 	timeout       time.Duration
 	spinner       *yacspin.Spinner
+	dryRun        bool
 }
 
+// BuilderOptionFunc is a function that configures a Builder
 type BuilderOptionFunc func(b *Builder) error
 
+// WithKustomizationFile sets the kustomization file
 func WithKustomizationFile(file string) BuilderOptionFunc {
 	return func(b *Builder) error {
 		b.kustomizationFile = file
 		return nil
 	}
 }
 
+// WithTimeout sets the timeout for the builder
 func WithTimeout(timeout time.Duration) BuilderOptionFunc {
 	return func(b *Builder) error {
 		b.timeout = timeout
@@ -116,24 +120,47 @@ func WithProgressBar() BuilderOptionFunc {
 	}
 }
 
-// NewBuilder returns a new Builder
-// to dp : create functional options
-func NewBuilder(rcg *genericclioptions.ConfigFlags, clientOpts *runclient.Options, name, resources string, opts ...BuilderOptionFunc) (*Builder, error) {
-	kubeClient, err := utils.KubeClient(rcg, clientOpts)
-	if err != nil {
-		return nil, err
+// WithClientConfig sets the client configuration
+func WithClientConfig(rcg *genericclioptions.ConfigFlags, clientOpts *runclient.Options) BuilderOptionFunc {
+	return func(b *Builder) error {
+		kubeClient, err := utils.KubeClient(rcg, clientOpts)
+		if err != nil {
+			return err
+		}
+
+		restMapper, err := rcg.ToRESTMapper()
+		if err != nil {
+			return err
+		}
+		b.client = kubeClient
+		b.restMapper = restMapper
+		b.namespace = *rcg.Namespace
+		return nil
 	}
+}
 
-	restMapper, err := rcg.ToRESTMapper()
-	if err != nil {
-		return nil, err
+// WithDryRun sets the dry-run flag
+func WithDryRun(dryRun bool) BuilderOptionFunc {
+	return func(b *Builder) error {
+		b.dryRun = dryRun
+		return nil
 	}
+}
 
+// NewBuilder returns a new Builder
+// It takes a kustomization name and a path to the resources
+// It also takes a list of BuilderOptionFunc to configure the builder
+// One of the options is WithClientConfig, that must be provided for the builder to work
+// with the k8s cluster
+// One other option is WithKustomizationFile, that must be provided for the builder to work
+// with a local kustomization file. If the kustomization file is not provided, the builder
+// will try to retrieve the kustomization object from the k8s cluster.
+// WithDryRun sets the dry-run flag, and needs to be provided if the builder is used for
+// a dry-run. This flag works in conjunction with WithKustomizationFile, because the
+// kustomization object is not retrieved from the k8s cluster when the dry-run flag is set.
+func NewBuilder(name, resources string, opts ...BuilderOptionFunc) (*Builder, error) {
 	b := &Builder{
-		client:        kubeClient,
-		restMapper:    restMapper,
 		name:          name,
-		namespace:     *rcg.Namespace,
 		resourcesPath: resources,
 	}
 
@@ -147,6 +174,14 @@ func NewBuilder(rcg *genericclioptions.ConfigFlags, clientOpts *runclient.Option
 		b.timeout = defaultTimeout
 	}
 
+	if b.dryRun && b.kustomizationFile == "" {
+		return nil, fmt.Errorf("kustomization file is required for dry-run")
+	}
+
+	if !b.dryRun && b.client == nil {
+		return nil, fmt.Errorf("client is required for live run")
+	}
+
 	return b, nil
 }
 
@@ -301,7 +336,7 @@ func (b *Builder) do(ctx context.Context, kustomization kustomizev1.Kustomizatio
 			if err != nil {
 				return nil, err
 			}
-			outRes, err := kustomize.SubstituteVariables(ctx, b.client, unstructured.Unstructured{Object: data}, res, false)
+			outRes, err := kustomize.SubstituteVariables(ctx, b.client, unstructured.Unstructured{Object: data}, res, b.dryRun)
 			if err != nil {
 				return nil, fmt.Errorf("var substitution failed for '%s': %w", res.GetName(), err)
 			}