Adding a kubelet flag to optionally enable parallel image pulls.

cmd/kubelet/app/server.go

@@ -146,6 +146,9 @@ type KubeletServer struct {
 
 	KubeApiQps   float32
 	KubeApiBurst int
+
+	// Pull images one at a time.
+	SerializeImagePulls bool
 }
 
 // bootstrapping interface for kubelet, targets the initialization protocol
@@ -185,6 +188,8 @@ func NewKubeletServer() *KubeletServer {
 		HTTPCheckFrequency:          20 * time.Second,
 		ImageGCHighThresholdPercent: 90,
 		ImageGCLowThresholdPercent:  80,
+		KubeApiQps:                  5.0,
+		KubeApiBurst:                10,
 		KubeConfig:                  util.NewStringFlag("/var/lib/kubelet/kubeconfig"),
 		LowDiskSpaceThresholdMB:     256,
 		MasterServiceNamespace:      api.NamespaceDefault,
@@ -199,6 +204,7 @@ func NewKubeletServer() *KubeletServer {
 		PodInfraContainerImage:      dockertools.PodInfraContainerImage,
 		Port:                ports.KubeletPort,
 		ReadOnlyPort:        ports.KubeletReadOnlyPort,
+		ReconcileCIDR:       true,
 		RegisterNode:        true, // will be ignored if no apiserver is configured
 		RegisterSchedulable: true,
 		RegistryBurst:       10,
@@ -208,9 +214,6 @@ func NewKubeletServer() *KubeletServer {
 		RootDirectory:       defaultRootDir,
 		SyncFrequency:       10 * time.Second,
 		SystemContainer:     "",
-		ReconcileCIDR:       true,
-		KubeApiQps:          5.0,
-		KubeApiBurst:        10,
 	}
 }
 
@@ -292,6 +295,7 @@ func (s *KubeletServer) AddFlags(fs *pflag.FlagSet) {
 	fs.BoolVar(&s.RegisterSchedulable, "register-schedulable", s.RegisterSchedulable, "Register the node as schedulable. No-op if register-node is false. [default=true]")
 	fs.Float32Var(&s.KubeApiQps, "kube-api-qps", s.KubeApiQps, "QPS to use while talking with kubernetes apiserver")
 	fs.IntVar(&s.KubeApiBurst, "kube-api-burst", s.KubeApiBurst, "Burst to use while talking with kubernetes apiserver")
+	fs.BoolVar(&s.SerializeImagePulls, "serialize-image-pulls", s.SerializeImagePulls, "Pull images one at a time. We recommend *not* changing the default value on nodes that run docker daemon with version < 1.9 or an Aufs storage backend. Issue #10959 has more details. [default=true]")
 }
 
 // UnsecuredKubeletConfig returns a KubeletConfig suitable for being run, or an error if the server setup
@@ -413,6 +417,7 @@ func (s *KubeletServer) UnsecuredKubeletConfig() (*KubeletConfig, error) {
 		RktStage1Image:                 s.RktStage1Image,
 		RootDirectory:                  s.RootDirectory,
 		Runonce:                        s.RunOnce,
+		SerializeImagePulls:            s.SerializeImagePulls,
 		StandaloneMode:                 (len(s.APIServerList) == 0),
 		StreamingConnectionIdleTimeout: s.StreamingConnectionIdleTimeout,
 		SyncFrequency:                  s.SyncFrequency,
@@ -672,6 +677,7 @@ func SimpleKubelet(client *client.Client,
 		ResolverConfig:      kubelet.ResolvConfDefault,
 		ResourceContainer:   "/kubelet",
 		RootDirectory:       rootDir,
+		SerializeImagePulls: true,
 		SyncFrequency:       syncFrequency,
 		SystemContainer:     "",
 		TLSOptions:          tlsOptions,
@@ -866,6 +872,7 @@ type KubeletConfig struct {
 	RktStage1Image                 string
 	RootDirectory                  string
 	Runonce                        bool
+	SerializeImagePulls            bool
 	StandaloneMode                 bool
 	StreamingConnectionIdleTimeout time.Duration
 	SyncFrequency                  time.Duration
@@ -948,7 +955,9 @@ func CreateAndInitKubelet(kc *KubeletConfig) (k KubeletBootstrap, pc *config.Pod
 		kc.ResolverConfig,
 		kc.CPUCFSQuota,
 		daemonEndpoints,
-		kc.OOMAdjuster)
+		kc.OOMAdjuster,
+		kc.SerializeImagePulls,
+	)
 
 	if err != nil {
 		return nil, nil, err

hack/verify-flags/known-flags.txt

@@ -257,6 +257,7 @@ runtime-config
 scheduler-config
 schema-cache-dir
 secure-port
+serialize-image-pulls
 service-account-key-file
 service-account-lookup
 service-account-private-key-file

pkg/kubelet/container/image_puller.go

@@ -18,7 +18,6 @@ package container
 
 import (
 	"fmt"
-	"time"
 
 	"github.com/golang/glog"
 	"k8s.io/kubernetes/pkg/api"
@@ -26,36 +25,26 @@ import (
 	"k8s.io/kubernetes/pkg/util"
 )
 
-type imagePullRequest struct {
-	spec        ImageSpec
-	container   *api.Container
-	pullSecrets []api.Secret
-	logPrefix   string
-	ref         *api.ObjectReference
-	returnChan  chan<- error
-}
-
 // imagePuller pulls the image using Runtime.PullImage().
 // It will check the presence of the image, and report the 'image pulling',
 // 'image pulled' events correspondingly.
-type serializedImagePuller struct {
+type imagePuller struct {
-	recorder     record.EventRecorder
+	recorder record.EventRecorder
-	runtime      Runtime
+	runtime  Runtime
-	backOff      *util.Backoff
+	backOff  *util.Backoff
-	pullRequests chan *imagePullRequest
 }
 
+// enforce compatibility.
+var _ ImagePuller = &imagePuller{}
+
 // NewImagePuller takes an event recorder and container runtime to create a
 // image puller that wraps the container runtime's PullImage interface.
-func NewSerializedImagePuller(recorder record.EventRecorder, runtime Runtime, imageBackOff *util.Backoff) ImagePuller {
+func NewImagePuller(recorder record.EventRecorder, runtime Runtime, imageBackOff *util.Backoff) ImagePuller {
-	imagePuller := &serializedImagePuller{
+	return &imagePuller{
-		recorder:     recorder,
+		recorder: recorder,
-		runtime:      runtime,
+		runtime:  runtime,
-		backOff:      imageBackOff,
+		backOff:  imageBackOff,
-		pullRequests: make(chan *imagePullRequest, 10),
 	}
-	go util.Until(imagePuller.pullImages, time.Second, util.NeverStop)
-	return imagePuller
 }
 
 // shouldPullImage returns whether we should pull an image according to
@@ -74,7 +63,7 @@ func shouldPullImage(container *api.Container, imagePresent bool) bool {
 }
 
 // records an event using ref, event msg.  log to glog using prefix, msg, logFn
-func (puller *serializedImagePuller) logIt(ref *api.ObjectReference, event, prefix, msg string, logFn func(args ...interface{})) {
+func (puller *imagePuller) logIt(ref *api.ObjectReference, event, prefix, msg string, logFn func(args ...interface{})) {
 	if ref != nil {
 		puller.recorder.Eventf(ref, event, msg)
 	} else {
@@ -83,7 +72,7 @@ func (puller *serializedImagePuller) logIt(ref *api.ObjectReference, event, pref
 }
 
 // PullImage pulls the image for the specified pod and container.
-func (puller *serializedImagePuller) PullImage(pod *api.Pod, container *api.Container, pullSecrets []api.Secret) (error, string) {
+func (puller *imagePuller) PullImage(pod *api.Pod, container *api.Container, pullSecrets []api.Secret) (error, string) {
 	logPrefix := fmt.Sprintf("%s/%s", pod.Name, container.Image)
 	ref, err := GenerateContainerRef(pod, container)
 	if err != nil {
@@ -116,18 +105,8 @@ func (puller *serializedImagePuller) PullImage(pod *api.Pod, container *api.Cont
 		puller.logIt(ref, "Back-off", logPrefix, msg, glog.Info)
 		return ErrImagePullBackOff, msg
 	}
-
+	puller.logIt(ref, "Pulling", logPrefix, fmt.Sprintf("pulling image %q", container.Image), glog.Info)
-	// enqueue image pull request and wait for response.
+	if err := puller.runtime.PullImage(spec, pullSecrets); err != nil {
-	returnChan := make(chan error)
-	puller.pullRequests <- &imagePullRequest{
-		spec:        spec,
-		container:   container,
-		pullSecrets: pullSecrets,
-		logPrefix:   logPrefix,
-		ref:         ref,
-		returnChan:  returnChan,
-	}
-	if err = <-returnChan; err != nil {
 		puller.logIt(ref, "Failed", logPrefix, fmt.Sprintf("Failed to pull image %q: %v", container.Image, err), glog.Warning)
 		puller.backOff.Next(backOffKey, puller.backOff.Clock.Now())
 		if err == RegistryUnavailable {
@@ -141,10 +120,3 @@ func (puller *serializedImagePuller) PullImage(pod *api.Pod, container *api.Cont
 	puller.backOff.GC()
 	return nil, ""
 }
-
-func (puller *serializedImagePuller) pullImages() {
-	for pullRequest := range puller.pullRequests {
-		puller.logIt(pullRequest.ref, "Pulling", pullRequest.logPrefix, fmt.Sprintf("pulling image %q", pullRequest.container.Image), glog.Info)
-		pullRequest.returnChan <- puller.runtime.PullImage(pullRequest.spec, pullRequest.pullSecrets)
-	}
-}

pkg/kubelet/container/image_puller_test.go

@@ -103,7 +103,7 @@ func TestPuller(t *testing.T) {
 
 		fakeRuntime := &FakeRuntime{}
 		fakeRecorder := &record.FakeRecorder{}
-		puller := NewSerializedImagePuller(fakeRecorder, fakeRuntime, backOff)
+		puller := NewImagePuller(fakeRecorder, fakeRuntime, backOff)
 
 		fakeRuntime.ImageList = []Image{{"present_image", nil, 0}}
 		fakeRuntime.Err = c.pullerErr
@@ -115,5 +115,6 @@ func TestPuller(t *testing.T) {
 			fakeRuntime.AssertCalls(c.calledFunctions)
 			assert.Equal(t, expected, err, "in test %d tick=%d", i, tick)
 		}
+
 	}
 }

pkg/kubelet/container/serialized_image_puller.go

@@ -0,0 +1,140 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package container
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/golang/glog"
+	"k8s.io/kubernetes/pkg/api"
+	"k8s.io/kubernetes/pkg/client/record"
+	"k8s.io/kubernetes/pkg/util"
+)
+
+type imagePullRequest struct {
+	spec        ImageSpec
+	container   *api.Container
+	pullSecrets []api.Secret
+	logPrefix   string
+	ref         *api.ObjectReference
+	returnChan  chan<- error
+}
+
+// serializedImagePuller pulls the image using Runtime.PullImage().
+// It will check the presence of the image, and report the 'image pulling',
+// 'image pulled' events correspondingly.
+type serializedImagePuller struct {
+	recorder     record.EventRecorder
+	runtime      Runtime
+	backOff      *util.Backoff
+	pullRequests chan *imagePullRequest
+}
+
+// enforce compatibility.
+var _ ImagePuller = &serializedImagePuller{}
+
+// NewSerializedImagePuller takes an event recorder and container runtime to create a
+// image puller that wraps the container runtime's PullImage interface.
+// Pulls one image at a time.
+// Issue #10959 has the rationale behind serializing image pulls.
+func NewSerializedImagePuller(recorder record.EventRecorder, runtime Runtime, imageBackOff *util.Backoff) ImagePuller {
+	imagePuller := &serializedImagePuller{
+		recorder:     recorder,
+		runtime:      runtime,
+		backOff:      imageBackOff,
+		pullRequests: make(chan *imagePullRequest, 10),
+	}
+	go util.Until(imagePuller.pullImages, time.Second, util.NeverStop)
+	return imagePuller
+}
+
+// records an event using ref, event msg.  log to glog using prefix, msg, logFn
+func (puller *serializedImagePuller) logIt(ref *api.ObjectReference, event, prefix, msg string, logFn func(args ...interface{})) {
+	if ref != nil {
+		puller.recorder.Eventf(ref, event, msg)
+	} else {
+		logFn(fmt.Sprint(prefix, " ", msg))
+	}
+}
+
+// PullImage pulls the image for the specified pod and container.
+func (puller *serializedImagePuller) PullImage(pod *api.Pod, container *api.Container, pullSecrets []api.Secret) (error, string) {
+	logPrefix := fmt.Sprintf("%s/%s", pod.Name, container.Image)
+	ref, err := GenerateContainerRef(pod, container)
+	if err != nil {
+		glog.Errorf("Couldn't make a ref to pod %v, container %v: '%v'", pod.Name, container.Name, err)
+	}
+
+	spec := ImageSpec{container.Image}
+	present, err := puller.runtime.IsImagePresent(spec)
+	if err != nil {
+		msg := fmt.Sprintf("Failed to inspect image %q: %v", container.Image, err)
+		puller.logIt(ref, "Failed", logPrefix, msg, glog.Warning)
+		return ErrImageInspect, msg
+	}
+
+	if !shouldPullImage(container, present) {
+		if present {
+			msg := fmt.Sprintf("Container image %q already present on machine", container.Image)
+			puller.logIt(ref, "Pulled", logPrefix, msg, glog.Info)
+			return nil, ""
+		} else {
+			msg := fmt.Sprintf("Container image %q is not present with pull policy of Never", container.Image)
+			puller.logIt(ref, "ErrImageNeverPull", logPrefix, msg, glog.Warning)
+			return ErrImageNeverPull, msg
+		}
+	}
+
+	backOffKey := fmt.Sprintf("%s_%s", pod.Name, container.Image)
+	if puller.backOff.IsInBackOffSinceUpdate(backOffKey, puller.backOff.Clock.Now()) {
+		msg := fmt.Sprintf("Back-off pulling image %q", container.Image)
+		puller.logIt(ref, "Back-off", logPrefix, msg, glog.Info)
+		return ErrImagePullBackOff, msg
+	}
+
+	// enqueue image pull request and wait for response.
+	returnChan := make(chan error)
+	puller.pullRequests <- &imagePullRequest{
+		spec:        spec,
+		container:   container,
+		pullSecrets: pullSecrets,
+		logPrefix:   logPrefix,
+		ref:         ref,
+		returnChan:  returnChan,
+	}
+	if err = <-returnChan; err != nil {
+		puller.logIt(ref, "Failed", logPrefix, fmt.Sprintf("Failed to pull image %q: %v", container.Image, err), glog.Warning)
+		puller.backOff.Next(backOffKey, puller.backOff.Clock.Now())
+		if err == RegistryUnavailable {
+			msg := fmt.Sprintf("image pull failed for %s because the registry is temporarily unavailable.", container.Image)
+			return err, msg
+		} else {
+			return ErrImagePull, err.Error()
+		}
+	}
+	puller.logIt(ref, "Pulled", logPrefix, fmt.Sprintf("Successfully pulled image %q", container.Image), glog.Info)
+	puller.backOff.GC()
+	return nil, ""
+}
+
+func (puller *serializedImagePuller) pullImages() {
+	for pullRequest := range puller.pullRequests {
+		puller.logIt(pullRequest.ref, "Pulling", pullRequest.logPrefix, fmt.Sprintf("pulling image %q", pullRequest.container.Image), glog.Info)
+		pullRequest.returnChan <- puller.runtime.PullImage(pullRequest.spec, pullRequest.pullSecrets)
+	}
+}

pkg/kubelet/container/serialized_image_puller_test.go

@@ -0,0 +1,120 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package container
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"k8s.io/kubernetes/pkg/api"
+	"k8s.io/kubernetes/pkg/client/record"
+	"k8s.io/kubernetes/pkg/util"
+)
+
+func TestSerializedPuller(t *testing.T) {
+	pod := &api.Pod{
+		ObjectMeta: api.ObjectMeta{
+			Name:            "test_pod",
+			Namespace:       "test-ns",
+			UID:             "bar",
+			ResourceVersion: "42",
+			SelfLink:        "/api/v1/pods/foo",
+		}}
+
+	cases := []struct {
+		containerImage  string
+		policy          api.PullPolicy
+		calledFunctions []string
+		inspectErr      error
+		pullerErr       error
+		expectedErr     []error
+	}{
+		{ // pull missing image
+			containerImage:  "missing_image",
+			policy:          api.PullIfNotPresent,
+			calledFunctions: []string{"IsImagePresent", "PullImage"},
+			inspectErr:      nil,
+			pullerErr:       nil,
+			expectedErr:     []error{nil}},
+
+		{ // image present, dont pull
+			containerImage:  "present_image",
+			policy:          api.PullIfNotPresent,
+			calledFunctions: []string{"IsImagePresent"},
+			inspectErr:      nil,
+			pullerErr:       nil,
+			expectedErr:     []error{nil, nil, nil}},
+		// image present, pull it
+		{containerImage: "present_image",
+			policy:          api.PullAlways,
+			calledFunctions: []string{"IsImagePresent", "PullImage"},
+			inspectErr:      nil,
+			pullerErr:       nil,
+			expectedErr:     []error{nil, nil, nil}},
+		// missing image, error PullNever
+		{containerImage: "missing_image",
+			policy:          api.PullNever,
+			calledFunctions: []string{"IsImagePresent"},
+			inspectErr:      nil,
+			pullerErr:       nil,
+			expectedErr:     []error{ErrImageNeverPull, ErrImageNeverPull, ErrImageNeverPull}},
+		// missing image, unable to inspect
+		{containerImage: "missing_image",
+			policy:          api.PullIfNotPresent,
+			calledFunctions: []string{"IsImagePresent"},
+			inspectErr:      errors.New("unknown inspectError"),
+			pullerErr:       nil,
+			expectedErr:     []error{ErrImageInspect, ErrImageInspect, ErrImageInspect}},
+		// missing image, unable to fetch
+		{containerImage: "typo_image",
+			policy:          api.PullIfNotPresent,
+			calledFunctions: []string{"IsImagePresent", "PullImage"},
+			inspectErr:      nil,
+			pullerErr:       errors.New("404"),
+			expectedErr:     []error{ErrImagePull, ErrImagePull, ErrImagePullBackOff, ErrImagePull, ErrImagePullBackOff, ErrImagePullBackOff}},
+	}
+
+	for i, c := range cases {
+		container := &api.Container{
+			Name:            "container_name",
+			Image:           c.containerImage,
+			ImagePullPolicy: c.policy,
+		}
+
+		backOff := util.NewBackOff(time.Second, time.Minute)
+		fakeClock := &util.FakeClock{Time: time.Now()}
+		backOff.Clock = fakeClock
+
+		fakeRuntime := &FakeRuntime{}
+		fakeRecorder := &record.FakeRecorder{}
+		puller := NewSerializedImagePuller(fakeRecorder, fakeRuntime, backOff)
+
+		fakeRuntime.ImageList = []Image{{"present_image", nil, 0}}
+		fakeRuntime.Err = c.pullerErr
+		fakeRuntime.InspectErr = c.inspectErr
+
+		for tick, expected := range c.expectedErr {
+			fakeClock.Step(time.Second)
+			err, _ := puller.PullImage(pod, container, nil)
+			fakeRuntime.AssertCalls(c.calledFunctions)
+			assert.Equal(t, expected, err, "in test %d tick=%d", i, tick)
+		}
+
+	}
+}

pkg/kubelet/dockertools/fake_manager.go

@@ -47,7 +47,7 @@ func NewFakeDockerManager(
 	fakeProcFs := procfs.NewFakeProcFs()
 	dm := NewDockerManager(client, recorder, livenessManager, containerRefManager, machineInfo, podInfraContainerImage, qps,
 		burst, containerLogsDir, osInterface, networkPlugin, generator, httpClient, &NativeExecHandler{},
-		fakeOOMAdjuster, fakeProcFs, false, imageBackOff)
+		fakeOOMAdjuster, fakeProcFs, false, imageBackOff, true)
 	dm.dockerPuller = &FakeDockerPuller{}
 	return dm
 }

pkg/kubelet/dockertools/manager.go

@@ -161,7 +161,8 @@ func NewDockerManager(
 	oomAdjuster *oom.OOMAdjuster,
 	procFs procfs.ProcFsInterface,
 	cpuCFSQuota bool,
-	imageBackOff *util.Backoff) *DockerManager {
+	imageBackOff *util.Backoff,
+	serializeImagePulls bool) *DockerManager {
 
 	// Work out the location of the Docker runtime, defaulting to /var/lib/docker
 	// if there are any problems.
@@ -215,7 +216,11 @@ func NewDockerManager(
 		cpuCFSQuota:            cpuCFSQuota,
 	}
 	dm.runner = lifecycle.NewHandlerRunner(httpClient, dm, dm)
-	dm.imagePuller = kubecontainer.NewSerializedImagePuller(recorder, dm, imageBackOff)
+	if serializeImagePulls {
+		dm.imagePuller = kubecontainer.NewSerializedImagePuller(recorder, dm, imageBackOff)
+	} else {
+		dm.imagePuller = kubecontainer.NewImagePuller(recorder, dm, imageBackOff)
+	}
 	dm.containerGC = NewContainerGC(client, containerLogsDir)
 
 	return dm

pkg/kubelet/kubelet.go

@@ -184,7 +184,9 @@ func NewMainKubelet(
 	resolverConfig string,
 	cpuCFSQuota bool,
 	daemonEndpoints *api.NodeDaemonEndpoints,
-	oomAdjuster *oom.OOMAdjuster) (*Kubelet, error) {
+	oomAdjuster *oom.OOMAdjuster,
+	serializeImagePulls bool,
+) (*Kubelet, error) {
 	if rootDirectory == "" {
 		return nil, fmt.Errorf("invalid root directory %q", rootDirectory)
 	}
@@ -335,7 +337,9 @@ func NewMainKubelet(
 			oomAdjuster,
 			procFs,
 			klet.cpuCFSQuota,
-			imageBackOff)
+			imageBackOff,
+			serializeImagePulls,
+		)
 
 	case "rkt":
 		conf := &rkt.Config{
@@ -350,7 +354,9 @@ func NewMainKubelet(
 			containerRefManager,
 			klet.livenessManager,
 			klet.volumeManager,
-			imageBackOff)
+			imageBackOff,
+			serializeImagePulls,
+		)
 		if err != nil {
 			return nil, err
 		}

pkg/kubelet/rkt/rkt.go

@@ -109,8 +109,9 @@ func New(config *Config,
 	containerRefManager *kubecontainer.RefManager,
 	livenessManager proberesults.Manager,
 	volumeGetter volumeGetter,
-	imageBackOff *util.Backoff) (*Runtime, error) {
+	imageBackOff *util.Backoff,
-
+	serializeImagePulls bool,
+) (*Runtime, error) {
 	systemdVersion, err := getSystemdVersion()
 	if err != nil {
 		return nil, err
@@ -149,7 +150,11 @@ func New(config *Config,
 		livenessManager:     livenessManager,
 		volumeGetter:        volumeGetter,
 	}
-	rkt.imagePuller = kubecontainer.NewSerializedImagePuller(recorder, rkt, imageBackOff)
+	if serializeImagePulls {
+		rkt.imagePuller = kubecontainer.NewSerializedImagePuller(recorder, rkt, imageBackOff)
+	} else {
+		rkt.imagePuller = kubecontainer.NewImagePuller(recorder, rkt, imageBackOff)
+	}
 
 	// Test the rkt version.
 	version, err := rkt.Version()