Only require docker for the docker runtime

Closes kubernetes#3295

README.md

@@ -139,7 +139,7 @@ the following drivers:
 * [hyperkit](https://github.com/kubernetes/minikube/blob/master/docs/drivers.md#hyperkit-driver)
 * [xhyve](https://github.com/kubernetes/minikube/blob/master/docs/drivers.md#xhyve-driver)
 * [hyperv](https://github.com/kubernetes/minikube/blob/master/docs/drivers.md#hyperV-driver)
-* none (**Linux + docker daemon as container runtime only**) - this driver can be used to run the Kubernetes cluster components on the host instead of in a VM. This can be useful for CI workloads which do not support nested virtualization.
+* none (**Linux-only**) - this driver can be used to run the Kubernetes cluster components on the host instead of in a VM. This can be useful for CI workloads which do not support nested virtualization.
 
 ```shell
 $ minikube start

cmd/minikube/cmd/start.go

@@ -141,6 +141,7 @@ func runStart(cmd *cobra.Command, args []string) {
 		CPUs:                viper.GetInt(cpus),
 		DiskSize:            diskSizeMB,
 		VMDriver:            viper.GetString(vmDriver),
+		ContainerRuntime:    viper.GetString(containerRuntime),
 		HyperkitVpnKitSock:  viper.GetString(vpnkitSock),
 		HyperkitVSockPorts:  viper.GetStringSlice(vsockPorts),
 		XhyveDiskDriver:     viper.GetString(xhyveDiskDriver),

pkg/drivers/none/none.go

@@ -40,7 +40,8 @@ var dockerkillcmd = fmt.Sprintf(`docker rm $(%s)`, dockerstopcmd)
 type Driver struct {
 	*drivers.BaseDriver
 	*pkgdrivers.CommonDriver
-	URL string
+	URL              string
+	ContainerRuntime string
 }
 
 func NewDriver(hostName, storePath string) *Driver {
@@ -54,11 +55,13 @@ func NewDriver(hostName, storePath string) *Driver {
 
 // PreCreateCheck checks for correct privileges and dependencies
 func (d *Driver) PreCreateCheck() error {
-	// check that docker is on path
-	_, err := exec.LookPath("docker")
-	if err != nil {
-		return errors.Wrap(err, "docker cannot be found on the path for this machine. "+
-			"A docker installation is a requirement for using the none driver")
+	if d.ContainerRuntime == "" {
+		// check that docker is on path
+		_, err := exec.LookPath("docker")
+		if err != nil {
+			return errors.Wrap(err, "docker cannot be found on the path for this machine. "+
+				"A docker installation is a requirement for using the none driver")
+		}
 	}
 
 	return nil

pkg/minikube/config/types.go

@@ -35,6 +35,7 @@ type MachineConfig struct {
 	CPUs                int
 	DiskSize            int
 	VMDriver            string
+	ContainerRuntime    string
 	HyperkitVpnKitSock  string   // Only used by the Hyperkit driver
 	HyperkitVSockPorts  []string // Only used by the Hyperkit driver
 	XhyveDiskDriver     string   // Only used by the xhyve driver

pkg/minikube/drivers/none/driver.go

@@ -43,5 +43,6 @@ func createNoneHost(config cfg.MachineConfig) interface{} {
 			MachineName: cfg.GetMachineName(),
 			StorePath:   constants.GetMinipath(),
 		},
+		ContainerRuntime: config.ContainerRuntime,
 	}
 }