feat(helm): add ability for --dry-run to do lookup functions

When a helm command is run with the --dry-run flag, it will try to connect to the cluster
to be able to render lookup functions.
Closes #8137

Signed-off-by: Tapas Kapadia <tapaskapadia10@gmail.com>

pkg/action/action.go

@@ -102,7 +102,7 @@ type Configuration struct {
 // TODO: This function is badly in need of a refactor.
 // TODO: As part of the refactor the duplicate code in cmd/helm/template.go should be removed
 //       This code has to do with writing files to disk.
-func (cfg *Configuration) renderResources(ch *chart.Chart, values chartutil.Values, releaseName, outputDir string, subNotes, useReleaseName, includeCrds bool, pr postrender.PostRenderer, dryRun bool) ([]*release.Hook, *bytes.Buffer, string, error) {
+func (cfg *Configuration) renderResources(ch *chart.Chart, values chartutil.Values, releaseName, outputDir string, subNotes, useReleaseName, includeCrds bool, pr postrender.PostRenderer, interactWithRemote bool) ([]*release.Hook, *bytes.Buffer, string, error) {
 	hs := []*release.Hook{}
 	b := bytes.NewBuffer(nil)
 
@@ -120,12 +120,12 @@ func (cfg *Configuration) renderResources(ch *chart.Chart, values chartutil.Valu
 	var files map[string]string
 	var err2 error
 
-	// A `helm template` or `helm install --dry-run` should not talk to the remote cluster.
-	// It will break in interesting and exotic ways because other data (e.g. discovery)
-	// is mocked. It is not up to the template author to decide when the user wants to
-	// connect to the cluster. So when the user says to dry run, respect the user's
-	// wishes and do not connect to the cluster.
-	if !dryRun && cfg.RESTClientGetter != nil {
+	// A `helm template`  should not talk to the remote cluster. However, commands
+	// with `--dry-run` should be able to try to connect to the cluster.
+	// This enables the ability to render 'lookup' functions.
+	// It may break in interesting and exotic ways because other data (e.g. discovery)
+	// is mocked.
+	if interactWithRemote && cfg.RESTClientGetter != nil {
 		restConfig, err := cfg.RESTClientGetter.ToRESTConfig()
 		if err != nil {
 			return hs, b, "", err

pkg/action/install.go

@@ -257,7 +257,12 @@ func (i *Install) RunWithContext(ctx context.Context, chrt *chart.Chart, vals ma
 	rel := i.createRelease(chrt, vals)
 
 	var manifestDoc *bytes.Buffer
-	rel.Hooks, manifestDoc, rel.Info.Notes, err = i.cfg.renderResources(chrt, valuesToRender, i.ReleaseName, i.OutputDir, i.SubNotes, i.UseReleaseName, i.IncludeCRDs, i.PostRenderer, i.DryRun)
+	// Determines whether `helm template` was used or another command with the --dry-run flag
+	// as they both set the Install.DryRun field to `true`. The `--dry-run` flag should be able
+	// to connect to remote for the lookup function. `helm template` is the only command that
+	// Install.APIVersions field will not be nil.
+	interactWithRemote := !i.DryRun || i.APIVersions == nil
+	rel.Hooks, manifestDoc, rel.Info.Notes, err = i.cfg.renderResources(chrt, valuesToRender, i.ReleaseName, i.OutputDir, i.SubNotes, i.UseReleaseName, i.IncludeCRDs, i.PostRenderer, interactWithRemote)
 	// Even for errors, attach this if available
 	if manifestDoc != nil {
 		rel.Manifest = manifestDoc.String()

pkg/action/install_test.go

@@ -254,7 +254,7 @@ func TestInstallRelease_DryRun(t *testing.T) {
 	is.Equal(res.Info.Description, "Dry run complete")
 }
 
-// Regression test for #7955: Lookup must not connect to Kubernetes on a dry-run.
+// Regression test for #7955
 func TestInstallRelease_DryRun_Lookup(t *testing.T) {
 	is := assert.New(t)
 	instAction := installAction(t)

pkg/action/upgrade.go

@@ -230,8 +230,8 @@ func (u *Upgrade) prepareUpgrade(name string, chart *chart.Chart, vals map[strin
 	if err != nil {
 		return nil, nil, err
 	}
-
-	hooks, manifestDoc, notesTxt, err := u.cfg.renderResources(chart, valuesToRender, "", "", u.SubNotes, false, false, u.PostRenderer, u.DryRun)
+	// Interacts with cluster if possible
+	hooks, manifestDoc, notesTxt, err := u.cfg.renderResources(chart, valuesToRender, "", "", u.SubNotes, false, false, u.PostRenderer, true)
 	if err != nil {
 		return nil, nil, err
 	}