Add convenience container-runtime flag for kubeadm

To enable the cri-o runtime you may now just use

`minikube start --container-runtime=cri-o --bootstrapper=kubeadm`
or
`minikube start --container-runtiume=crio --bootstrapper=kubeadm`
or
`minikube start --extra-config=kubelet.container-runtime=remote
--extra-config=kubelet.container-runtime-endpoint=/var/run/crio.sock
--extra-config=image-service-endpoint=/var/run/crio.sock`

pkg/minikube/bootstrapper/kubeadm/kubeadm.go

@@ -27,6 +27,7 @@ import (
 
 	"github.com/docker/machine/libmachine"
 	"github.com/docker/machine/libmachine/state"
+	"github.com/golang/glog"
 	download "github.com/jimmidyson/go-download"
 	"github.com/pkg/errors"
 	"golang.org/x/sync/errgroup"
@@ -178,6 +179,35 @@ func (k *KubeadmBootstrapper) SetupCerts(k8s bootstrapper.KubernetesConfig) erro
 	return bootstrapper.SetupCerts(k.c, k8s)
 }
 
+// SetContainerRuntime possibly sets the container runtime, if it hasn't already
+// been specified by the extra-config option.  It has a set of defaults known to
+// work for a particular runtime.
+func SetContainerRuntime(cfg map[string]string, runtime string) map[string]string {
+	if _, ok := cfg["container-runtime"]; ok {
+		glog.Infoln("Container runtime already set through extra options, ignoring --container-runtime flag.")
+		return cfg
+	}
+
+	if runtime == "" {
+		glog.Infoln("Container runtime flag provided with no value, using defaults.")
+		return cfg
+	}
+
+	switch runtime {
+	case "crio", "cri-o":
+		cfg["container-runtime"] = "remote"
+		cfg["container-runtime-endpoint"] = "/var/run/crio.sock"
+		cfg["image-service-endpoint"] = "/var/run/crio.sock"
+		cfg["runtime-request-timeout"] = "15m"
+	default:
+		cfg["container-runtime"] = runtime
+	}
+
+	return cfg
+}
+
+// NewKubeletConfig generates a new systemd unit containing a configured kubelet
+// based on the options present in the KubernetesConfig.
 func NewKubeletConfig(k8s bootstrapper.KubernetesConfig) (string, error) {
 	version, err := ParseKubernetesVersion(k8s.KubernetesVersion)
 	if err != nil {
@@ -189,14 +219,17 @@ func NewKubeletConfig(k8s bootstrapper.KubernetesConfig) (string, error) {
 		return "", errors.Wrap(err, "generating extra configuration for kubelet")
 	}
 
+	extraOpts = SetContainerRuntime(extraOpts, k8s.ContainerRuntime)
 	extraFlags := convertToFlags(extraOpts)
 	b := bytes.Buffer{}
 	opts := struct {
-		ExtraOptions string
-		FeatureGates string
+		ExtraOptions     string
+		FeatureGates     string
+		ContainerRuntime string
 	}{
-		ExtraOptions: extraFlags,
-		FeatureGates: k8s.FeatureGates,
+		ExtraOptions:     extraFlags,
+		FeatureGates:     k8s.FeatureGates,
+		ContainerRuntime: k8s.ContainerRuntime,
 	}
 	if err := kubeletSystemdTemplate.Execute(&b, opts); err != nil {
 		return "", err

pkg/minikube/bootstrapper/kubeadm/templates.go

@@ -40,17 +40,31 @@ nodeName: {{.NodeName}}
   {{$val}}{{end}}
 {{end}}`))
 
-var kubeletSystemdTemplate = template.Must(template.New("kubeletSystemdTemplate").Parse(`
+var kubeletSystemdTemplate = template.Must(template.New("kubeletSystemdTemplate").Funcs(template.FuncMap{
+	"installWants": installWants,
+}).Parse(`
 [Service]
-Environment="KUBELET_KUBECONFIG_ARGS=--kubeconfig=/etc/kubernetes/kubelet.conf --require-kubeconfig=true"
-Environment="KUBELET_SYSTEM_PODS_ARGS=--pod-manifest-path=/etc/kubernetes/manifests --allow-privileged=true"
-Environment="KUBELET_DNS_ARGS=--cluster-dns=10.0.0.10 --cluster-domain=cluster.local"
-Environment="KUBELET_CADVISOR_ARGS=--cadvisor-port=0"
-Environment="KUBELET_CGROUP_ARGS=--cgroup-driver=cgroupfs"
 ExecStart=
-ExecStart=/usr/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_SYSTEM_PODS_ARGS $KUBELET_DNS_ARGS $KUBELET_CADVISOR_ARGS $KUBELET_CGROUP_ARGS {{.ExtraOptions}} {{if .FeatureGates}}--feature-gates={{.FeatureGates}}{{end}}
+ExecStart=/usr/bin/kubelet {{.ExtraOptions}} {{if .FeatureGates}}--feature-gates={{.FeatureGates}}{{end}}
+
+[Install]
+{{installWants .ContainerRuntime}}
 `))
 
+func installWants(containerRuntime string) string {
+	var wants string
+	switch containerRuntime {
+	case "":
+		wants = "docker.socket"
+	case "cri-o", "cri":
+		wants = "crio.service"
+	}
+	if wants != "" {
+		return fmt.Sprintf("Wants=%s", wants)
+	}
+	return ""
+}
+
 const kubeletService = `
 [Unit]
 Description=kubelet: The Kubernetes Node Agent

pkg/minikube/bootstrapper/kubeadm/versions.go

@@ -149,6 +149,17 @@ type VersionedExtraOption struct {
 	GreaterThanOrEqual semver.Version
 }
 
+// NewUnversionedOption returns a VersionedExtraOption that applies to all versions.
+func NewUnversionedOption(component, k, v string) VersionedExtraOption {
+	return VersionedExtraOption{
+		Option: util.ExtraOption{
+			Component: component,
+			Key:       k,
+			Value:     v,
+		},
+	}
+}
+
 var versionSpecificOpts = []VersionedExtraOption{
 	{
 		Option: util.ExtraOption{
@@ -158,6 +169,14 @@ var versionSpecificOpts = []VersionedExtraOption{
 		},
 		GreaterThanOrEqual: semver.MustParse("1.8.0-alpha.0"),
 	},
+	NewUnversionedOption(Kubelet, "kubeconfig", "/etc/kubernetes/kubelet.conf"),
+	NewUnversionedOption(Kubelet, "require-kubeconfig", "true"),
+	NewUnversionedOption(Kubelet, "pod-manifest-path", "/etc/kubernetes/manifests"),
+	NewUnversionedOption(Kubelet, "allow-privileged", "true"),
+	NewUnversionedOption(Kubelet, "cluster-dns", "10.0.0.10"),
+	NewUnversionedOption(Kubelet, "cluster-domain", "cluster.local"),
+	NewUnversionedOption(Kubelet, "cadvisor-port", "0"),
+	NewUnversionedOption(Kubelet, "cgroup-driver", "cgroupfs"),
 }
 
 func VersionIsBetween(version, gte, lte semver.Version) bool {