Add option for fluxctl install to write to files

It's pretty useful to be able to get a flux config as individual
files, so you can e.g., check them into git. This also means we can
use `fluxctl install` to generate the files under deploy/, so they
will be reliably close to what you'd get from running the tool.

cmd/fluxctl/install_cmd.go

@@ -2,14 +2,19 @@ package main
 
 import (
 	"fmt"
+	"io/ioutil"
 	"os"
+	"path/filepath"
 
 	"github.com/spf13/cobra"
 
 	"github.com/fluxcd/flux/pkg/install"
 )
 
-type installOpts install.TemplateParameters
+type installOpts struct {
+	install.TemplateParameters
+	outputDir string
+}
 
 func newInstall() *installOpts {
 	return &installOpts{}
@@ -23,22 +28,23 @@ func (opts *installOpts) Command() *cobra.Command {
 fluxctl install --git-url '[email protected]:<your username>/flux-get-started' | kubectl -f -`,
 		RunE: opts.RunE,
 	}
-	cmd.Flags().StringVarP(&opts.GitURL, "git-url", "", "",
+	cmd.Flags().StringVar(&opts.GitURL, "git-url", "",
 		"URL of the Git repository to be used by Flux, e.g. [email protected]:<your username>/flux-get-started")
-	cmd.Flags().StringVarP(&opts.GitBranch, "git-branch", "", "master",
+	cmd.Flags().StringVar(&opts.GitBranch, "git-branch", "master",
 		"Git branch to be used by Flux")
-	cmd.Flags().StringSliceVarP(&opts.GitPaths, "git-paths", "", []string{},
+	cmd.Flags().StringSliceVar(&opts.GitPaths, "git-paths", []string{},
 		"Relative paths within the Git repo for Flux to locate Kubernetes manifests")
-	cmd.Flags().StringSliceVarP(&opts.GitPaths, "git-path", "", []string{},
+	cmd.Flags().StringSliceVar(&opts.GitPaths, "git-path", []string{},
 		"Relative paths within the Git repo for Flux to locate Kubernetes manifests")
-	cmd.Flags().StringVarP(&opts.GitLabel, "git-label", "", "flux",
+	cmd.Flags().StringVar(&opts.GitLabel, "git-label", "flux",
 		"Git label to keep track of Flux's sync progress; overrides both --git-sync-tag and --git-notes-ref")
-	cmd.Flags().StringVarP(&opts.GitUser, "git-user", "", "Flux",
+	cmd.Flags().StringVar(&opts.GitUser, "git-user", "Flux",
 		"Username to use as git committer")
-	cmd.Flags().StringVarP(&opts.GitEmail, "git-email", "", "",
+	cmd.Flags().StringVar(&opts.GitEmail, "git-email", "",
 		"Email to use as git committer")
-	cmd.Flags().StringVarP(&opts.Namespace, "namespace", "", getKubeConfigContextNamespace("default"),
+	cmd.Flags().StringVar(&opts.Namespace, "namespace", getKubeConfigContextNamespace("default"),
 		"Cluster namespace where to install flux")
+	cmd.Flags().StringVarP(&opts.outputDir, "output-dir", "o", "", "a directory in which to write individual manifests, rather than printing to stdout")
 
 	// Hide and deprecate "git-paths", which was wrongly introduced since its inconsistent with fluxd's git-path flag
 	cmd.Flags().MarkHidden("git-paths")
@@ -54,15 +60,35 @@ func (opts *installOpts) RunE(cmd *cobra.Command, args []string) error {
 	if opts.GitEmail == "" {
 		return fmt.Errorf("please supply a valid --git-email argument")
 	}
-	manifests, err := install.FillInTemplates(install.TemplateParameters(*opts))
+	manifests, err := install.FillInTemplates(opts.TemplateParameters)
 	if err != nil {
 		return err
 	}
+
+	writeManifest := func(fileName string, content []byte) error {
+		_, err := os.Stdout.Write(content)
+		return err
+	}
+
+	if opts.outputDir != "" {
+		info, err := os.Stat(opts.outputDir)
+		if err != nil {
+			return err
+		}
+		if !info.IsDir() {
+			return fmt.Errorf("%s is not a directory", opts.outputDir)
+		}
+		writeManifest = func(fileName string, content []byte) error {
+			path := filepath.Join(opts.outputDir, fileName)
+			fmt.Fprintf(os.Stderr, "writing %s\n", path)
+			return ioutil.WriteFile(path, content, os.FileMode(0666))
+		}
+	}
+
 	for fileName, content := range manifests {
-		if _, err := os.Stdout.Write(content); err != nil {
+		if err := writeManifest(fileName, content); err != nil {
 			return fmt.Errorf("cannot output manifest file %s: %s", fileName, err)
 		}
-
 	}
 
 	return nil