Make the default container runtime dynamic

Since the dockershim removal, there is no longer a constant
default container runtime provided by upstream. Only CRI.

cmd/minikube/cmd/docker-env.go

@@ -280,7 +280,7 @@ var dockerEnvCmd = &cobra.Command{
 			exit.Message(reason.EnvMultiConflict, `The docker-env command is incompatible with multi-node clusters. Use the 'registry' add-on: https://minikube.sigs.k8s.io/docs/handbook/registry/`)
 		}
 
-		if co.Config.KubernetesConfig.ContainerRuntime != "docker" {
+		if co.Config.KubernetesConfig.ContainerRuntime != constants.Docker {
 			exit.Message(reason.Usage, `The docker-env command is only compatible with the "docker" runtime, but this cluster was configured to use the "{{.runtime}}" runtime.`,
 				out.V{"runtime": co.Config.KubernetesConfig.ContainerRuntime})
 		}

cmd/minikube/cmd/podman-env.go

@@ -170,6 +170,11 @@ var podmanEnvCmd = &cobra.Command{
 			exit.Message(reason.Usage, `The podman-env command is incompatible with multi-node clusters. Use the 'registry' add-on: https://minikube.sigs.k8s.io/docs/handbook/registry/`)
 		}
 
+		if co.Config.KubernetesConfig.ContainerRuntime != constants.CRIO {
+			exit.Message(reason.Usage, `The podman-env command is only compatible with the "crio" runtime, but this cluster was configured to use the "{{.runtime}}" runtime.`,
+				out.V{"runtime": co.Config.KubernetesConfig.ContainerRuntime})
+		}
+
 		r := co.CP.Runner
 		if ok := isPodmanAvailable(r); !ok {
 			exit.Message(reason.EnvPodmanUnavailable, `The podman service within '{{.cluster}}' is not active`, out.V{"cluster": cname})

cmd/minikube/cmd/start.go

@@ -188,6 +188,7 @@ func runStart(cmd *cobra.Command, args []string) {
 
 	validateSpecifiedDriver(existing)
 	validateKubernetesVersion(existing)
+	validateContainerRuntime(existing)
 
 	ds, alts, specified := selectDriver(existing)
 	if cmd.Flag(kicBaseImage).Changed {
@@ -270,7 +271,7 @@ func runStart(cmd *cobra.Command, args []string) {
 		exit.Error(reason.GuestStart, "failed to start node", err)
 	}
 
-	if err := showKubectlInfo(kubeconfig, starter.Node.KubernetesVersion, starter.Cfg.Name); err != nil {
+	if err := showKubectlInfo(kubeconfig, starter.Node.KubernetesVersion, starter.Node.ContainerRuntime, starter.Cfg.Name); err != nil {
 		klog.Errorf("kubectl info: %v", err)
 	}
 }
@@ -302,7 +303,8 @@ func provisionWithDriver(cmd *cobra.Command, ds registry.DriverState, existing *
 	}
 
 	k8sVersion := getKubernetesVersion(existing)
-	cc, n, err := generateClusterConfig(cmd, existing, k8sVersion, driverName)
+	rtime := getContainerRuntime(existing)
+	cc, n, err := generateClusterConfig(cmd, existing, k8sVersion, rtime, driverName)
 	if err != nil {
 		return node.Starter{}, errors.Wrap(err, "Failed to generate config")
 	}
@@ -381,6 +383,7 @@ func startWithDriver(cmd *cobra.Command, starter node.Starter, existing *config.
 						Worker:            true,
 						ControlPlane:      false,
 						KubernetesVersion: starter.Cfg.KubernetesConfig.KubernetesVersion,
+						ContainerRuntime:  starter.Cfg.KubernetesConfig.ContainerRuntime,
 					}
 					out.Ln("") // extra newline for clarity on the command line
 					err := node.Add(starter.Cfg, n, viper.GetBool(deleteOnFailure))
@@ -439,15 +442,15 @@ func displayEnviron(env []string) {
 	}
 }
 
-func showKubectlInfo(kcs *kubeconfig.Settings, k8sVersion, machineName string) error {
+func showKubectlInfo(kcs *kubeconfig.Settings, k8sVersion, rtime, machineName string) error {
 	if k8sVersion == constants.NoKubernetesVersion {
 		register.Reg.SetStep(register.Done)
 		out.Step(style.Ready, "Done! minikube is ready without Kubernetes!")
 
 		// Runtime message.
 		boxConfig := box.Config{Py: 1, Px: 4, Type: "Round", Color: "Green"}
-		switch viper.GetString(containerRuntime) {
-		case constants.DefaultContainerRuntime:
+		switch rtime {
+		case constants.Docker:
 			out.BoxedWithConfig(boxConfig, style.Tip, "Things to try without Kubernetes ...", `- "minikube ssh" to SSH into minikube's node.
 - "minikube docker-env" to point your docker-cli to the docker inside minikube.
 - "minikube image" to build images without docker.`)
@@ -1183,9 +1186,10 @@ func validateFlags(cmd *cobra.Command, drvName string) {
 			exit.Message(reason.DrvUnsupportedProfile, "The '{{.name}} driver does not support multiple profiles: https://minikube.sigs.k8s.io/docs/reference/drivers/none/", out.V{"name": drvName})
 		}
 
-		runtime := viper.GetString(containerRuntime)
-		if runtime != "docker" {
-			out.WarningT("Using the '{{.runtime}}' runtime with the 'none' driver is an untested configuration!", out.V{"runtime": runtime})
+		// default container runtime varies, starting with Kubernetes 1.24 - assume that only the default container runtime has been tested
+		rtime := viper.GetString(containerRuntime)
+		if rtime != constants.DefaultContainerRuntime && rtime != defaultRuntime(getKubernetesVersion(nil)) {
+			out.WarningT("Using the '{{.runtime}}' runtime with the 'none' driver is an untested configuration!", out.V{"runtime": rtime})
 		}
 
 		// conntrack is required starting with Kubernetes 1.18, include the release candidates for completion
@@ -1285,6 +1289,10 @@ func validateRuntime(rtime string) error {
 	// `crio` is accepted as an alternative spelling to `cri-o`
 	validOptions = append(validOptions, constants.CRIO)
 
+	if rtime == constants.DefaultContainerRuntime {
+		return nil
+	}
+
 	var validRuntime bool
 	for _, option := range validOptions {
 		if rtime == option {
@@ -1308,9 +1316,31 @@ func validateRuntime(rtime string) error {
 	return nil
 }
 
+func getContainerRuntime(old *config.ClusterConfig) string {
+	paramRuntime := viper.GetString(containerRuntime)
+
+	// try to load the old version first if the user didn't specify anything
+	if paramRuntime == constants.DefaultContainerRuntime && old != nil {
+		paramRuntime = old.KubernetesConfig.ContainerRuntime
+	}
+
+	if paramRuntime == constants.DefaultContainerRuntime {
+		k8sVersion := getKubernetesVersion(old)
+		paramRuntime = defaultRuntime(k8sVersion)
+	}
+
+	return paramRuntime
+}
+
+// defaultRuntime returns the default container runtime
+func defaultRuntime(k8sVersion string) string {
+	// minikube default
+	return constants.Docker
+}
+
 // if container runtime is not docker, check that cni is not disabled
 func validateCNI(cmd *cobra.Command, runtime string) {
-	if runtime == "docker" {
+	if runtime == constants.Docker {
 		return
 	}
 	if cmd.Flags().Changed(cniFlag) && strings.ToLower(viper.GetString(cniFlag)) == "false" {
@@ -1458,6 +1488,7 @@ func createNode(cc config.ClusterConfig, kubeNodeName string, existing *config.C
 	if existing != nil {
 		cp, err := config.PrimaryControlPlane(existing)
 		cp.KubernetesVersion = getKubernetesVersion(&cc)
+		cp.ContainerRuntime = getContainerRuntime(&cc)
 		if err != nil {
 			return cc, config.Node{}, err
 		}
@@ -1467,6 +1498,7 @@ func createNode(cc config.ClusterConfig, kubeNodeName string, existing *config.C
 		nodes := []config.Node{}
 		for _, n := range existing.Nodes {
 			n.KubernetesVersion = getKubernetesVersion(&cc)
+			n.ContainerRuntime = getContainerRuntime(&cc)
 			nodes = append(nodes, n)
 		}
 		cc.Nodes = nodes
@@ -1477,6 +1509,7 @@ func createNode(cc config.ClusterConfig, kubeNodeName string, existing *config.C
 	cp := config.Node{
 		Port:              cc.KubernetesConfig.NodePort,
 		KubernetesVersion: getKubernetesVersion(&cc),
+		ContainerRuntime:  getContainerRuntime(&cc),
 		Name:              kubeNodeName,
 		ControlPlane:      true,
 		Worker:            true,
@@ -1573,6 +1606,17 @@ func validateKubernetesVersion(old *config.ClusterConfig) {
 	}
 }
 
+// validateContainerRuntime ensures that the container runtime is reasonable
+func validateContainerRuntime(old *config.ClusterConfig) {
+	if old == nil || old.KubernetesConfig.ContainerRuntime == "" {
+		return
+	}
+
+	if err := validateRuntime(old.KubernetesConfig.ContainerRuntime); err != nil {
+		klog.Errorf("Error parsing old runtime %q: %v", old.KubernetesConfig.ContainerRuntime, err)
+	}
+}
+
 func isBaseImageApplicable(drv string) bool {
 	return registry.IsKIC(drv)
 }

cmd/minikube/cmd/start_flags.go

@@ -158,7 +158,7 @@ func initMinikubeFlags() {
 	startCmd.Flags().String(kicBaseImage, kic.BaseImage, "The base image to use for docker/podman drivers. Intended for local development.")
 	startCmd.Flags().Bool(keepContext, false, "This will keep the existing kubectl context and will create a minikube context.")
 	startCmd.Flags().Bool(embedCerts, false, "if true, will embed the certs in kubeconfig.")
-	startCmd.Flags().String(containerRuntime, constants.DefaultContainerRuntime, fmt.Sprintf("The container runtime to be used (%s).", strings.Join(cruntime.ValidRuntimes(), ", ")))
+	startCmd.Flags().String(containerRuntime, constants.DefaultContainerRuntime, fmt.Sprintf("The container runtime to be used. Valid options: %s (default: auto)", strings.Join(cruntime.ValidRuntimes(), ", ")))
 	startCmd.Flags().Bool(createMount, false, "This will start the mount daemon and automatically mount files into minikube.")
 	startCmd.Flags().String(mountString, constants.DefaultMountDir+":/minikube-host", "The argument to pass the minikube mount command on start.")
 	startCmd.Flags().String(mount9PVersion, defaultMount9PVersion, mount9PVersionDescription)
@@ -270,7 +270,7 @@ func ClusterFlagValue() string {
 }
 
 // generateClusterConfig generate a config.ClusterConfig based on flags or existing cluster config
-func generateClusterConfig(cmd *cobra.Command, existing *config.ClusterConfig, k8sVersion string, drvName string) (config.ClusterConfig, config.Node, error) {
+func generateClusterConfig(cmd *cobra.Command, existing *config.ClusterConfig, k8sVersion string, rtime string, drvName string) (config.ClusterConfig, config.Node, error) {
 	var cc config.ClusterConfig
 	if existing != nil {
 		cc = updateExistingConfigFromFlags(cmd, existing)
@@ -282,7 +282,7 @@ func generateClusterConfig(cmd *cobra.Command, existing *config.ClusterConfig, k
 		}
 	} else {
 		klog.Info("no existing cluster config was found, will generate one from the flags ")
-		cc = generateNewConfigFromFlags(cmd, k8sVersion, drvName)
+		cc = generateNewConfigFromFlags(cmd, k8sVersion, rtime, drvName)
 
 		cnm, err := cni.New(&cc)
 		if err != nil {
@@ -419,7 +419,7 @@ func getCNIConfig(cmd *cobra.Command) string {
 }
 
 // generateNewConfigFromFlags generate a config.ClusterConfig based on flags
-func generateNewConfigFromFlags(cmd *cobra.Command, k8sVersion string, drvName string) config.ClusterConfig {
+func generateNewConfigFromFlags(cmd *cobra.Command, k8sVersion string, rtime string, drvName string) config.ClusterConfig {
 	var cc config.ClusterConfig
 
 	// networkPlugin cni deprecation warning
@@ -499,7 +499,7 @@ func generateNewConfigFromFlags(cmd *cobra.Command, k8sVersion string, drvName s
 			APIServerIPs:           apiServerIPs,
 			DNSDomain:              viper.GetString(dnsDomain),
 			FeatureGates:           viper.GetString(featureGates),
-			ContainerRuntime:       viper.GetString(containerRuntime),
+			ContainerRuntime:       rtime,
 			CRISocket:              viper.GetString(criSocket),
 			NetworkPlugin:          chosenNetworkPlugin,
 			ServiceCIDR:            viper.GetString(serviceCIDR),
@@ -533,7 +533,7 @@ func generateNewConfigFromFlags(cmd *cobra.Command, k8sVersion string, drvName s
 			exit.Message(reason.Usage, "Ensure your {{.driver_name}} is running and is healthy.", out.V{"driver_name": driver.FullName(drvName)})
 		}
 		if si.Rootless {
-			if cc.KubernetesConfig.ContainerRuntime == "docker" {
+			if cc.KubernetesConfig.ContainerRuntime == constants.Docker {
 				exit.Message(reason.Usage, "--container-runtime must be set to \"containerd\" or \"cri-o\" for rootless")
 			}
 			// KubeletInUserNamespace feature gate is essential for rootless driver.
@@ -711,6 +711,9 @@ func updateExistingConfigFromFlags(cmd *cobra.Command, existing *config.ClusterC
 	if cmd.Flags().Changed(kubernetesVersion) {
 		cc.KubernetesConfig.KubernetesVersion = getKubernetesVersion(existing)
 	}
+	if cmd.Flags().Changed(containerRuntime) {
+		cc.KubernetesConfig.ContainerRuntime = getContainerRuntime(existing)
+	}
 
 	if cmd.Flags().Changed("extra-config") {
 		cc.KubernetesConfig.ExtraOptions = config.ExtraOptions

cmd/minikube/cmd/start_test.go

@@ -112,6 +112,7 @@ func TestMirrorCountry(t *testing.T) {
 	viper.SetDefault(humanReadableDiskSize, defaultDiskSize)
 	checkRepository = checkRepoMock
 	k8sVersion := constants.DefaultKubernetesVersion
+	rtime := constants.DefaultContainerRuntime
 	var tests = []struct {
 		description     string
 		k8sVersion      string
@@ -157,7 +158,7 @@ func TestMirrorCountry(t *testing.T) {
 			viper.SetDefault(imageRepository, test.imageRepository)
 			viper.SetDefault(imageMirrorCountry, test.mirrorCountry)
 			viper.SetDefault(kvmNUMACount, 1)
-			config, _, err := generateClusterConfig(cmd, nil, k8sVersion, driver.Mock)
+			config, _, err := generateClusterConfig(cmd, nil, k8sVersion, rtime, driver.Mock)
 			if err != nil {
 				t.Fatalf("Got unexpected error %v during config generation", err)
 			}
@@ -179,6 +180,7 @@ func TestGenerateCfgFromFlagsHTTPProxyHandling(t *testing.T) {
 		}
 	}()
 	k8sVersion := constants.NewestKubernetesVersion
+	rtime := constants.DefaultContainerRuntime
 	var tests = []struct {
 		description  string
 		proxy        string
@@ -226,7 +228,7 @@ func TestGenerateCfgFromFlagsHTTPProxyHandling(t *testing.T) {
 
 			cfg.DockerEnv = []string{} // clear docker env to avoid pollution
 			proxy.SetDockerEnv()
-			config, _, err := generateClusterConfig(cmd, nil, k8sVersion, "none")
+			config, _, err := generateClusterConfig(cmd, nil, k8sVersion, rtime, "none")
 			if err != nil {
 				t.Fatalf("Got unexpected error %v during config generation", err)
 			}

pkg/minikube/cni/cni.go

@@ -155,7 +155,7 @@ func chooseDefault(cc config.ClusterConfig) Manager {
 		return KindNet{cc: cc}
 	}
 
-	if cc.KubernetesConfig.ContainerRuntime != "docker" {
+	if cc.KubernetesConfig.ContainerRuntime != constants.Docker {
 		if driver.IsKIC(cc.Driver) {
 			klog.Infof("%q driver + %s runtime found, recommending kindnet", cc.Driver, cc.KubernetesConfig.ContainerRuntime)
 			return KindNet{cc: cc}

pkg/minikube/cni/disabled.go

@@ -19,6 +19,7 @@ package cni
 import (
 	"k8s.io/klog/v2"
 	"k8s.io/minikube/pkg/minikube/config"
+	"k8s.io/minikube/pkg/minikube/constants"
 	"k8s.io/minikube/pkg/minikube/driver"
 )
 
@@ -34,7 +35,7 @@ func (c Disabled) String() string {
 
 // Apply enables the CNI
 func (c Disabled) Apply(r Runner) error {
-	if driver.IsKIC(c.cc.Driver) && c.cc.KubernetesConfig.ContainerRuntime != "docker" {
+	if driver.IsKIC(c.cc.Driver) && c.cc.KubernetesConfig.ContainerRuntime != constants.Docker {
 		klog.Warningf("CNI is recommended for %q driver and %q runtime - expect networking issues", c.cc.Driver, c.cc.KubernetesConfig.ContainerRuntime)
 	}
 

pkg/minikube/config/profile.go

@@ -63,6 +63,7 @@ func PrimaryControlPlane(cc *ClusterConfig) (Node, error) {
 		IP:                cc.KubernetesConfig.NodeIP,
 		Port:              cc.KubernetesConfig.NodePort,
 		KubernetesVersion: cc.KubernetesConfig.KubernetesVersion,
+		ContainerRuntime:  cc.KubernetesConfig.ContainerRuntime,
 		ControlPlane:      true,
 		Worker:            true,
 	}

pkg/minikube/config/types.go

@@ -134,6 +134,7 @@ type Node struct {
 	IP                string
 	Port              int
 	KubernetesVersion string
+	ContainerRuntime  string
 	ControlPlane      bool
 	Worker            bool
 }

pkg/minikube/constants/constants.go

@@ -60,8 +60,10 @@ const (
 	Containerd = "containerd"
 	// CRIO is the default name and spelling for the cri-o container runtime
 	CRIO = "crio"
+	// Docker is the default name and spelling for the docker container runtime
+	Docker = "docker"
 	// DefaultContainerRuntime is our default container runtime
-	DefaultContainerRuntime = "docker"
+	DefaultContainerRuntime = ""
 
 	// APIServerName is the default API server name
 	APIServerName = "minikubeCA"

pkg/minikube/download/download_test.go

@@ -94,7 +94,7 @@ func testPreloadDownloadPreventsMultipleDownload(t *testing.T) {
 	var group sync.WaitGroup
 	group.Add(2)
 	dlCall := func() {
-		if err := Preload(constants.DefaultKubernetesVersion, constants.DefaultContainerRuntime, "docker"); err != nil {
+		if err := Preload(constants.DefaultKubernetesVersion, constants.Docker, "docker"); err != nil {
 			t.Logf("Failed to download preload: %+v (may be ok)", err)
 		}
 		group.Done()
@@ -119,7 +119,7 @@ func testPreloadNotExists(t *testing.T) {
 	getChecksum = func(k8sVersion, containerRuntime string) ([]byte, error) { return []byte("check"), nil }
 	ensureChecksumValid = func(k8sVersion, containerRuntime, path string, checksum []byte) error { return nil }
 
-	err := Preload(constants.DefaultKubernetesVersion, constants.DefaultContainerRuntime, "docker")
+	err := Preload(constants.DefaultKubernetesVersion, constants.Docker, "docker")
 	if err != nil {
 		t.Errorf("Expected no error when preload exists")
 	}
@@ -140,7 +140,7 @@ func testPreloadChecksumMismatch(t *testing.T) {
 		return fmt.Errorf("checksum mismatch")
 	}
 
-	err := Preload(constants.DefaultKubernetesVersion, constants.DefaultContainerRuntime, "docker")
+	err := Preload(constants.DefaultKubernetesVersion, constants.Docker, "docker")
 	expectedErrMsg := "checksum mismatch"
 	if err == nil {
 		t.Errorf("Expected error when checksum mismatches")

site/content/en/docs/commands/start.md

@@ -30,7 +30,7 @@ minikube start [flags]
       --cache-images                      If true, cache docker images for the current bootstrapper and load them into the machine. Always false with --driver=none. (default true)
       --cert-expiration duration          Duration until minikube certificate expiration, defaults to three years (26280h). (default 26280h0m0s)
       --cni string                        CNI plug-in to use. Valid options: auto, bridge, calico, cilium, flannel, kindnet, or path to a CNI manifest (default: auto)
-      --container-runtime string          The container runtime to be used (docker, cri-o, containerd). (default "docker")
+      --container-runtime string          The container runtime to be used. Valid options: docker, cri-o, containerd (default: auto)
       --cpus string                       Number of CPUs allocated to Kubernetes. Use "max" to use the maximum number of CPUs. (default "2")
       --cri-socket string                 The cri socket path to be used.
       --delete-on-failure                 If set, delete the current cluster if start fails and try again. Defaults to false.

site/content/en/docs/handbook/config.md

@@ -89,7 +89,7 @@ minikube start --extra-config=kubeadm.ignore-preflight-errors=SystemVerification
 
 ## Runtime configuration
 
-The default container runtime in minikube is Docker. You can select it explicitly by using:
+The default container runtime in minikube varies. You can select one explicitly by using:
 
 ```shell
 minikube start --container-runtime=docker
@@ -100,6 +100,8 @@ Other options available are:
 * [containerd](https://github.com/containerd/containerd)
 * [cri-o](https://github.com/cri-o/cri-o)
 
+See <https://kubernetes.io/docs/setup/production-environment/container-runtimes/>
+
 ## Environment variables
 
 minikube supports passing environment variables instead of flags for every value listed in `minikube config`.  This is done by passing an environment variable with the prefix `MINIKUBE_`.

translations/strings.txt

@@ -647,6 +647,7 @@
 	"The path on the file system where the testing docs in markdown need to be saved": "",
 	"The podman service within '{{.cluster}}' is not active": "",
 	"The podman-env command is incompatible with multi-node clusters. Use the 'registry' add-on: https://minikube.sigs.k8s.io/docs/handbook/registry/": "",
+	"The podman-env command is only compatible with the \"crio\" runtime, but this cluster was configured to use the \"{{.runtime}}\" runtime.": "",
 	"The requested memory allocation of {{.requested}}MiB does not leave room for system overhead (total system memory: {{.system_limit}}MiB). You may face stability issues.": "",
 	"The service namespace": "",
 	"The service/ingress {{.resource}} requires privileged ports to be exposed: {{.ports}}": "",