Add --download-only option to start command

Make it possible to download files without loading or installing,
and without starting the host... Download: ISO, binaries, images.

cmd/minikube/cmd/cache.go

@@ -81,6 +81,18 @@ func imagesInConfigFile() ([]string, error) {
 	return []string{}, nil
 }
 
+// CacheImagesInConfigFile caches the images currently in the config file (minikube start)
+func CacheImagesInConfigFile() error {
+	images, err := imagesInConfigFile()
+	if err != nil {
+		return err
+	}
+	if len(images) == 0 {
+		return nil
+	}
+	return machine.CacheImages(images, constants.ImageCacheDir)
+}
+
 // LoadCachedImagesInConfigFile loads the images currently in the config file (minikube start)
 func LoadCachedImagesInConfigFile() error {
 	images, err := imagesInConfigFile()

cmd/minikube/cmd/start.go

@@ -87,6 +87,7 @@ const (
 	hidden                = "hidden"
 	embedCerts            = "embed-certs"
 	noVTXCheck            = "no-vtx-check"
+	downloadOnly          = "download-only"
 )
 
 var (
@@ -136,6 +137,7 @@ func init() {
 	startCmd.Flags().Bool(enableDefaultCNI, false, "Enable the default CNI plugin (/etc/cni/net.d/k8s.conf). Used in conjunction with \"--network-plugin=cni\"")
 	startCmd.Flags().String(featureGates, "", "A set of key=value pairs that describe feature gates for alpha/experimental features.")
 	startCmd.Flags().Bool(cacheImages, true, "If true, cache docker images for the current bootstrapper and load them into the machine.")
+	startCmd.Flags().Bool(downloadOnly, false, "If true, only download and cache files for later use - don't install or start anything.")
 	startCmd.Flags().Var(&extraOptions, "extra-config",
 		`A set of key=value pairs that describe configuration that may be passed to different components.
 		The key should be '.' separated, and the first part before the dot is the component to apply the configuration to.
@@ -187,6 +189,22 @@ func runStart(cmd *cobra.Command, args []string) {
 	if err != nil {
 		exit.WithError("Failed to get machine client", err)
 	}
+
+	if viper.GetBool(downloadOnly) {
+		if err := cluster.CacheISO(config.MachineConfig); err != nil {
+			exit.WithError("Failed to cache ISO", err)
+		}
+		if err := doCacheBinaries(k8sVersion); err != nil {
+			exit.WithError("Failed to cache binaries", err)
+		}
+		waitCacheImages(&cacheGroup)
+		if err := CacheImagesInConfigFile(); err != nil {
+			exit.WithError("Failed to cache images", err)
+		}
+		console.OutStyle("check", "Download complete!")
+		return
+	}
+
 	host, preexisting := startHost(m, config.MachineConfig)
 
 	ip := validateNetwork(host)
@@ -245,6 +263,11 @@ func validateConfig() {
 	}
 }
 
+// doCacheBinaries caches Kubernetes binaries in the foreground
+func doCacheBinaries(k8sVersion string) error {
+	return machine.CacheBinariesForBootstrapper(k8sVersion, viper.GetString(cmdcfg.Bootstrapper))
+}
+
 // beginCacheImages caches Docker images in the background
 func beginCacheImages(g *errgroup.Group, k8sVersion string) {
 	if !viper.GetBool(cacheImages) {

pkg/minikube/bootstrapper/bootstrapper.go

@@ -51,6 +51,16 @@ const (
 	BootstrapperTypeKubeadm = "kubeadm"
 )
 
+// GetCachedBinaryList returns the list of binaries
+func GetCachedBinaryList(bootstrapper string) []string {
+	switch bootstrapper {
+	case BootstrapperTypeKubeadm:
+		return constants.GetKubeadmCachedBinaries()
+	default:
+		return []string{}
+	}
+}
+
 // GetCachedImageList returns the list of images for a version
 func GetCachedImageList(imageRepository string, version string, bootstrapper string) []string {
 	switch bootstrapper {

pkg/minikube/console/style.go

@@ -69,6 +69,7 @@ var styles = map[string]style{
 	"documentation": {Prefix: "🗎   "},
 	"issues":        {Prefix: "📚  "},
 	"issue":         {Prefix: "    ▪ "}, // Indented bullet
+	"check":         {Prefix: "✔️  "},
 
 	// Specialized purpose styles
 	"iso-download":      {Prefix: "💿  ", LowPrefix: "@   "},

pkg/minikube/machine/cache_binaries.go

@@ -31,6 +31,23 @@ import (
 	"k8s.io/minikube/pkg/minikube/constants"
 )
 
+// CacheBinariesForBootstrapper will cache binaries for a bootstrapper
+func CacheBinariesForBootstrapper(version string, clusterBootstrapper string) error {
+	binaries := bootstrapper.GetCachedBinaryList(clusterBootstrapper)
+
+	var g errgroup.Group
+	for _, bin := range binaries {
+		bin := bin
+		g.Go(func() error {
+			if _, err := CacheBinary(bin, version); err != nil {
+				return errors.Wrapf(err, "caching image %s", bin)
+			}
+			return nil
+		})
+	}
+	return g.Wait()
+}
+
 // CacheBinary will cache a binary on the host
 func CacheBinary(binary, version string) (string, error) {
 	targetDir := constants.MakeMiniPath("cache", version)