Add a rollingupdate lib and command to kubectl

Also decouple conditions from client for testability.

cmd/integration/integration.go

@@ -251,7 +251,7 @@ func runReplicationControllerTest(c *client.Client) {
 	glog.Infof("Done creating replication controllers")
 
 	// Give the controllers some time to actually create the pods
-	if err := wait.Poll(time.Second, time.Second*30, c.ControllerHasDesiredReplicas(controller)); err != nil {
+	if err := wait.Poll(time.Second, time.Second*30, client.ControllerHasDesiredReplicas(c, &controller)); err != nil {
 		glog.Fatalf("FAILED: pods never created %v", err)
 	}
 

pkg/client/conditions.go

@@ -18,18 +18,17 @@ package client
 
 import (
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
-	"github.com/GoogleCloudPlatform/kubernetes/pkg/labels"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/util/wait"
 )
 
 // ControllerHasDesiredReplicas returns a condition that will be true iff the desired replica count
 // for a controller's ReplicaSelector equals the Replicas count.
-func (c *Client) ControllerHasDesiredReplicas(controller api.ReplicationController) wait.ConditionFunc {
+func ControllerHasDesiredReplicas(c Interface, controller *api.ReplicationController) wait.ConditionFunc {
 	return func() (bool, error) {
-		pods, err := c.Pods(controller.Namespace).List(labels.Set(controller.Spec.Selector).AsSelector())
+		ctrl, err := c.ReplicationControllers(controller.Namespace).Get(controller.Name)
 		if err != nil {
 			return false, err
 		}
-		return len(pods.Items) == controller.Spec.Replicas, nil
+		return ctrl.Status.Replicas == ctrl.Spec.Replicas, nil
 	}
 }

pkg/kubectl/cmd/cmd.go

@@ -118,6 +118,7 @@ Find more information at https://github.com/GoogleCloudPlatform/kubernetes.`,
 
 	cmds.AddCommand(NewCmdNamespace(out))
 	cmds.AddCommand(f.NewCmdLog(out))
+	cmds.AddCommand(f.NewCmdRollingUpdate(out))
 
 	if err := cmds.Execute(); err != nil {
 		os.Exit(1)

pkg/kubectl/cmd/helpers.go

@@ -24,6 +24,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/golang/glog"
 	"github.com/spf13/cobra"
@@ -82,6 +83,16 @@ func GetFlagInt(cmd *cobra.Command, flag string) int {
 	return v
 }
 
+func GetFlagDuration(cmd *cobra.Command, flag string) time.Duration {
+	f := cmd.Flags().Lookup(flag)
+	if f == nil {
+		glog.Fatalf("Flag accessed but not defined for command %s: %s", cmd.Name(), flag)
+	}
+	v, err := time.ParseDuration(f.Value.String())
+	checkErr(err)
+	return v
+}
+
 // Returns the first non-empty string out of the ones provided. If all
 // strings are empty, returns an empty string.
 func FirstNonEmptyString(args ...string) string {

pkg/kubectl/cmd/rollingupdate.go

@@ -0,0 +1,109 @@
+/*
+Copyright 2014 Google Inc. 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 cmd
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/kubectl"
+	"github.com/spf13/cobra"
+)
+
+const (
+	updatePeriod = "1m0s"
+	timeout      = "5m0s"
+	pollInterval = "3s"
+)
+
+func (f *Factory) NewCmdRollingUpdate(out io.Writer) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "rollingupdate <old-controller-name> -f <new-controller.json>",
+		Short: "Perform a rolling update of the given replicationController",
+		Long: `Perform a rolling update of the given replicationController.",
+
+Replaces named controller with new controller, updating one pod at a time to use the
+new PodTemplate. The new-controller.json must specify the same namespace as the
+existing controller and overwrite at least one (common) label in its replicaSelector.
+
+Examples:
+$ kubectl rollingupdate frontend-v1 -f frontend-v2.json
+  <update pods of frontend-v1 using new controller data in frontend-v2.json>
+
+$ cat frontend-v2.json | kubectl rollingupdate frontend-v1 -f -
+  <update pods of frontend-v1 using json data passed into stdin>`,
+		Run: func(cmd *cobra.Command, args []string) {
+			filename := GetFlagString(cmd, "filename")
+			if len(filename) == 0 {
+				usageError(cmd, "Must specify filename for new controller")
+			}
+			period := GetFlagDuration(cmd, "update-period")
+			interval := GetFlagDuration(cmd, "poll-interval")
+			timeout := GetFlagDuration(cmd, "timeout")
+			if len(args) != 1 {
+				usageError(cmd, "Must specify the controller to update")
+			}
+			oldName := args[0]
+			schema, err := f.Validator(cmd)
+			checkErr(err)
+			mapping, namespace, newName, data := ResourceFromFile(cmd, filename, f.Typer, f.Mapper, schema)
+			if mapping.Kind != "ReplicationController" {
+				usageError(cmd, "%s does not specify a valid ReplicationController", filename)
+			}
+			err = CompareNamespaceFromFile(cmd, namespace)
+			checkErr(err)
+
+			client, err := f.ClientBuilder.Client()
+			checkErr(err)
+			obj, err := mapping.Codec.Decode(data)
+			checkErr(err)
+			newRc := obj.(*api.ReplicationController)
+
+			updater := kubectl.NewRollingUpdater(namespace, client)
+
+			// fetch rc
+			oldRc, err := client.ReplicationControllers(namespace).Get(oldName)
+			checkErr(err)
+
+			var hasLabel bool
+			for key, oldValue := range oldRc.Spec.Selector {
+				if newValue, ok := newRc.Spec.Selector[key]; ok && newValue != oldValue {
+					hasLabel = true
+					break
+				}
+			}
+			if !hasLabel {
+				usageError(cmd, "%s must specify a matching key with non-equal value in Selector for %s",
+					filename, oldName)
+			}
+			// TODO: handle resizes during rolling update
+			if newRc.Spec.Replicas == 0 {
+				newRc.Spec.Replicas = oldRc.Spec.Replicas
+			}
+			err = updater.Update(out, oldRc, newRc, period, interval, timeout)
+			checkErr(err)
+
+			fmt.Fprintf(out, "%s\n", newName)
+		},
+	}
+	cmd.Flags().String("update-period", updatePeriod, `Time to wait between updating pods. Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".`)
+	cmd.Flags().String("poll-interval", pollInterval, `Time delay between polling controller status after update. Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".`)
+	cmd.Flags().String("timeout", timeout, `Max time to wait for a controller to update before giving up. Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".`)
+	cmd.Flags().StringP("filename", "f", "", "Filename or URL to file to use to create the new controller")
+	return cmd
+}

pkg/kubectl/kubectl.go

@@ -34,6 +34,8 @@ import (
 
 var apiVersionToUse = "v1beta1"
 
+const kubectlAnnotationPrefix = "kubectl.kubernetes.io/"
+
 func GetKubeClient(config *client.Config, matchVersion bool) (*client.Client, error) {
 	// TODO: get the namespace context when kubectl ns is completed
 	c, err := client.New(config)

pkg/kubectl/rolling_updater.go

@@ -0,0 +1,173 @@
+/*
+Copyright 2014 Google Inc. 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 kubectl
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+	"time"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/client"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/util/wait"
+)
+
+// RollingUpdater provides methods for updating replicated pods in a predictable,
+// fault-tolerant way.
+type RollingUpdater struct {
+	// Client interface for creating and updating controllers
+	c client.Interface
+	// Namespace for resources
+	ns string
+}
+
+// NewRollingUpdater creates a RollingUpdater from a client
+func NewRollingUpdater(namespace string, c client.Interface) *RollingUpdater {
+	return &RollingUpdater{
+		c,
+		namespace,
+	}
+}
+
+const (
+	sourceIdAnnotation        = kubectlAnnotationPrefix + "update-source-id"
+	desiredReplicasAnnotation = kubectlAnnotationPrefix + "desired-replicas"
+)
+
+// Update all pods for a ReplicationController (oldRc) by creating a new controller (newRc)
+// with 0 replicas, and synchronously resizing oldRc,newRc by 1 until oldRc has 0 replicas
+// and newRc has the original # of desired replicas. oldRc is then deleted.
+// If an update from newRc to oldRc is already in progress, we attempt to drive it to completion.
+// If an error occurs at any step of the update, the error will be returned.
+//  'out' writer for progress output
+//  'oldRc' existing controller to be replaced
+//  'newRc' controller that will take ownership of updated pods (will be created if needed)
+//  'updatePeriod' time to wait between individual pod updates
+//  'interval' time to wait between polling controller status after update
+//  'timeout' time to wait for controller updates before giving up
+//
+// TODO: make this handle performing a rollback of a partially completed rollout.
+func (r *RollingUpdater) Update(out io.Writer, oldRc, newRc *api.ReplicationController, updatePeriod, interval, timeout time.Duration) error {
+	oldName := oldRc.ObjectMeta.Name
+	newName := newRc.ObjectMeta.Name
+
+	if newRc.Spec.Replicas <= 0 {
+		return fmt.Errorf("Invalid controller spec for %s; required: > 0 replicas, actual: %s\n", newName, newRc.Spec)
+	}
+	desired := newRc.Spec.Replicas
+	sourceId := fmt.Sprintf("%s:%s", oldName, oldRc.ObjectMeta.UID)
+
+	// look for existing newRc, incase this update was previously started but interrupted
+	rc, existing, err := r.getExistingNewRc(sourceId, newName)
+	if existing {
+		fmt.Fprintf(out, "Continuing update with existing controller %s.\n", newName)
+		if err != nil {
+			return err
+		}
+		replicas := rc.ObjectMeta.Annotations[desiredReplicasAnnotation]
+		desired, err = strconv.Atoi(replicas)
+		if err != nil {
+			return fmt.Errorf("Unable to parse annotation for %s: %s=%s",
+				newName, desiredReplicasAnnotation, replicas)
+		}
+		newRc = rc
+	} else {
+		fmt.Fprintf(out, "Creating %s\n", newName)
+		if newRc.ObjectMeta.Annotations == nil {
+			newRc.ObjectMeta.Annotations = map[string]string{}
+		}
+		newRc.ObjectMeta.Annotations[desiredReplicasAnnotation] = fmt.Sprintf("%d", desired)
+		newRc.ObjectMeta.Annotations[sourceIdAnnotation] = sourceId
+		newRc.Spec.Replicas = 0
+		newRc, err = r.c.ReplicationControllers(r.ns).Create(newRc)
+		if err != nil {
+			return err
+		}
+	}
+
+	// +1, -1 on oldRc, newRc until newRc has desired number of replicas or oldRc has 0 replicas
+	for newRc.Spec.Replicas < desired && oldRc.Spec.Replicas != 0 {
+		newRc.Spec.Replicas += 1
+		oldRc.Spec.Replicas -= 1
+		fmt.Fprintf(out, "Updating %s replicas: %d, %s replicas: %d\n",
+			oldName, oldRc.Spec.Replicas,
+			newName, newRc.Spec.Replicas)
+
+		newRc, err = r.updateAndWait(newRc, interval, timeout)
+		if err != nil {
+			return err
+		}
+		time.Sleep(updatePeriod)
+		oldRc, err = r.updateAndWait(oldRc, interval, timeout)
+		if err != nil {
+			return err
+		}
+	}
+	// delete remaining replicas on oldRc
+	if oldRc.Spec.Replicas != 0 {
+		fmt.Fprintf(out, "Stopping %s replicas: %d -> %d\n",
+			oldName, oldRc.Spec.Replicas, 0)
+		oldRc.Spec.Replicas = 0
+		oldRc, err = r.updateAndWait(oldRc, interval, timeout)
+		if err != nil {
+			return err
+		}
+	}
+	// add remaining replicas on newRc, cleanup annotations
+	if newRc.Spec.Replicas != desired {
+		fmt.Fprintf(out, "Resizing %s replicas: %d -> %d\n",
+			newName, newRc.Spec.Replicas, desired)
+		newRc.Spec.Replicas = desired
+	}
+	delete(newRc.ObjectMeta.Annotations, sourceIdAnnotation)
+	delete(newRc.ObjectMeta.Annotations, desiredReplicasAnnotation)
+	newRc, err = r.updateAndWait(newRc, interval, timeout)
+	if err != nil {
+		return err
+	}
+	// delete old rc
+	fmt.Fprintf(out, "Update succeeded. Deleting %s\n", oldName)
+	return r.c.ReplicationControllers(r.ns).Delete(oldName)
+}
+
+func (r *RollingUpdater) getExistingNewRc(sourceId, name string) (rc *api.ReplicationController, existing bool, err error) {
+	if rc, err = r.c.ReplicationControllers(r.ns).Get(name); err == nil {
+		existing = true
+		annotations := rc.ObjectMeta.Annotations
+		source := annotations[sourceIdAnnotation]
+		_, ok := annotations[desiredReplicasAnnotation]
+		if source != sourceId || !ok {
+			err = fmt.Errorf("Missing/unexpected annotations for controller %s: %s", name, annotations)
+		}
+		return
+	}
+	err = nil
+	return
+}
+
+func (r *RollingUpdater) updateAndWait(rc *api.ReplicationController, interval, timeout time.Duration) (*api.ReplicationController, error) {
+	rc, err := r.c.ReplicationControllers(r.ns).Update(rc)
+	if err != nil {
+		return nil, err
+	}
+	if err := wait.Poll(interval, timeout,
+		client.ControllerHasDesiredReplicas(r.c, rc)); err != nil {
+		return nil, err
+	}
+	return r.c.ReplicationControllers(r.ns).Get(rc.ObjectMeta.Name)
+}

pkg/kubectl/rolling_updater_test.go

@@ -0,0 +1,276 @@
+/*
+Copyright 2014 Google Inc. 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 kubectl
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/client"
+)
+
+type customFake struct {
+	*client.Fake
+	ctrl client.ReplicationControllerInterface
+}
+
+func (c *customFake) ReplicationControllers(namespace string) client.ReplicationControllerInterface {
+	return c.ctrl
+}
+
+func fakeClientFor(namespace string, responses []fakeResponse) client.Interface {
+	fake := client.Fake{}
+	return &customFake{
+		&fake,
+		&fakeRc{
+			&client.FakeReplicationControllers{
+				Fake:      &fake,
+				Namespace: namespace,
+			},
+			responses,
+		},
+	}
+}
+
+type fakeResponse struct {
+	controller *api.ReplicationController
+	err        error
+}
+
+type fakeRc struct {
+	*client.FakeReplicationControllers
+	responses []fakeResponse
+}
+
+func (c *fakeRc) Get(name string) (*api.ReplicationController, error) {
+	action := client.FakeAction{Action: "get-controller", Value: name}
+	if len(c.responses) == 0 {
+		return nil, fmt.Errorf("Unexpected Action: %s", action)
+	}
+	c.Fake.Actions = append(c.Fake.Actions, action)
+	result := c.responses[0]
+	c.responses = c.responses[1:]
+	return result.controller, result.err
+}
+
+func (c *fakeRc) Create(controller *api.ReplicationController) (*api.ReplicationController, error) {
+	c.Fake.Actions = append(c.Fake.Actions, client.FakeAction{Action: "create-controller", Value: controller.ObjectMeta.Name})
+	return controller, nil
+}
+
+func (c *fakeRc) Update(controller *api.ReplicationController) (*api.ReplicationController, error) {
+	c.Fake.Actions = append(c.Fake.Actions, client.FakeAction{Action: "update-controller", Value: controller.ObjectMeta.Name})
+	return controller, nil
+}
+
+func oldRc(replicas int) *api.ReplicationController {
+	return &api.ReplicationController{
+		ObjectMeta: api.ObjectMeta{
+			Name: "foo-v1",
+			UID:  "7764ae47-9092-11e4-8393-42010af018ff",
+		},
+		Spec: api.ReplicationControllerSpec{
+			Replicas: replicas,
+			Selector: map[string]string{"version": "v1"},
+			Template: &api.PodTemplateSpec{
+				ObjectMeta: api.ObjectMeta{
+					Name:   "foo-v1",
+					Labels: map[string]string{"version": "v1"},
+				},
+			},
+		},
+		Status: api.ReplicationControllerStatus{
+			Replicas: replicas,
+		},
+	}
+}
+
+func newRc(replicas int, desired int) *api.ReplicationController {
+	rc := oldRc(replicas)
+	rc.Spec.Template = &api.PodTemplateSpec{
+		ObjectMeta: api.ObjectMeta{
+			Name:   "foo-v2",
+			Labels: map[string]string{"version": "v2"},
+		},
+	}
+	rc.Spec.Selector = map[string]string{"version": "v2"}
+	rc.ObjectMeta = api.ObjectMeta{
+		Name: "foo-v2",
+		Annotations: map[string]string{
+			desiredReplicasAnnotation: fmt.Sprintf("%d", desired),
+			sourceIdAnnotation:        "foo-v1:7764ae47-9092-11e4-8393-42010af018ff",
+		},
+	}
+	return rc
+}
+
+func TestUpdate(t *testing.T) {
+	tests := []struct {
+		oldRc, newRc *api.ReplicationController
+		responses    []fakeResponse
+		output       string
+	}{
+		{
+			oldRc(1), newRc(1, 1),
+			[]fakeResponse{
+				// no existing newRc
+				{nil, fmt.Errorf("not found")},
+				// one update round
+				{newRc(1, 1), nil},
+				{newRc(1, 1), nil},
+				{oldRc(0), nil},
+				{oldRc(0), nil},
+				// get newRc after final update (to cleanup annotations)
+				{newRc(1, 1), nil},
+				{newRc(1, 1), nil},
+			},
+			`Creating foo-v2
+Updating foo-v1 replicas: 0, foo-v2 replicas: 1
+Update succeeded. Deleting foo-v1
+`,
+		}, {
+			oldRc(2), newRc(2, 2),
+			[]fakeResponse{
+				// no existing newRc
+				{nil, fmt.Errorf("not found")},
+				// 2 gets for each update (poll for condition, refetch)
+				{newRc(1, 2), nil},
+				{newRc(1, 2), nil},
+				{oldRc(1), nil},
+				{oldRc(1), nil},
+				{newRc(2, 2), nil},
+				{newRc(2, 2), nil},
+				{oldRc(0), nil},
+				{oldRc(0), nil},
+				// get newRc after final update (cleanup annotations)
+				{newRc(2, 2), nil},
+				{newRc(2, 2), nil},
+			},
+			`Creating foo-v2
+Updating foo-v1 replicas: 1, foo-v2 replicas: 1
+Updating foo-v1 replicas: 0, foo-v2 replicas: 2
+Update succeeded. Deleting foo-v1
+`,
+		}, {
+			oldRc(2), newRc(7, 7),
+			[]fakeResponse{
+				// no existing newRc
+				{nil, fmt.Errorf("not found")},
+				// 2 gets for each update (poll for condition, refetch)
+				{newRc(1, 2), nil},
+				{newRc(1, 2), nil},
+				{oldRc(1), nil},
+				{oldRc(1), nil},
+				{newRc(2, 2), nil},
+				{newRc(2, 2), nil},
+				{oldRc(0), nil},
+				{oldRc(0), nil},
+				// final update on newRc (resize + cleanup annotations)
+				{newRc(7, 7), nil},
+				{newRc(7, 7), nil},
+			},
+			`Creating foo-v2
+Updating foo-v1 replicas: 1, foo-v2 replicas: 1
+Updating foo-v1 replicas: 0, foo-v2 replicas: 2
+Resizing foo-v2 replicas: 2 -> 7
+Update succeeded. Deleting foo-v1
+`,
+		}, {
+			oldRc(7), newRc(2, 2),
+			[]fakeResponse{
+				// no existing newRc
+				{nil, fmt.Errorf("not found")},
+				// 2 gets for each update (poll for condition, refetch)
+				{newRc(1, 2), nil},
+				{newRc(1, 2), nil},
+				{oldRc(6), nil},
+				{oldRc(6), nil},
+				{newRc(2, 2), nil},
+				{newRc(2, 2), nil},
+				{oldRc(5), nil},
+				{oldRc(5), nil},
+				// stop oldRc
+				{oldRc(0), nil},
+				{oldRc(0), nil},
+				// final update on newRc (cleanup annotations)
+				{newRc(2, 2), nil},
+				{newRc(2, 2), nil},
+			},
+			`Creating foo-v2
+Updating foo-v1 replicas: 6, foo-v2 replicas: 1
+Updating foo-v1 replicas: 5, foo-v2 replicas: 2
+Stopping foo-v1 replicas: 5 -> 0
+Update succeeded. Deleting foo-v1
+`,
+		},
+	}
+
+	for _, test := range tests {
+		updater := RollingUpdater{
+			fakeClientFor("default", test.responses),
+			"default",
+		}
+		var buffer bytes.Buffer
+
+		if err := updater.Update(&buffer, test.oldRc, test.newRc, 0, 1*time.Millisecond, 1*time.Millisecond); err != nil {
+			t.Errorf("Update failed: %v", err)
+		}
+		if buffer.String() != test.output {
+			t.Errorf("Bad output. expected:\n%s\ngot:\n%s", test.output, buffer.String())
+		}
+	}
+}
+
+func TestUpdateRecovery(t *testing.T) {
+	// Test recovery from interruption
+	rc := oldRc(2)
+	rcExisting := newRc(1, 3)
+
+	output := `Continuing update with existing controller foo-v2.
+Updating foo-v1 replicas: 1, foo-v2 replicas: 2
+Updating foo-v1 replicas: 0, foo-v2 replicas: 3
+Update succeeded. Deleting foo-v1
+`
+	responses := []fakeResponse{
+		// Existing newRc
+		{rcExisting, nil},
+		// 2 gets for each update (poll for condition, refetch)
+		{newRc(2, 2), nil},
+		{newRc(2, 2), nil},
+		{oldRc(1), nil},
+		{oldRc(1), nil},
+		{newRc(3, 3), nil},
+		{newRc(3, 3), nil},
+		{oldRc(0), nil},
+		{oldRc(0), nil},
+		// get newRc after final update (cleanup annotations)
+		{newRc(3, 3), nil},
+		{newRc(3, 3), nil},
+	}
+	updater := RollingUpdater{fakeClientFor("default", responses), "default"}
+
+	var buffer bytes.Buffer
+	if err := updater.Update(&buffer, rc, rcExisting, 0, 1*time.Millisecond, 1*time.Millisecond); err != nil {
+		t.Errorf("Update failed: %v", err)
+	}
+	if buffer.String() != output {
+		t.Errorf("Output was not as expected. Expected:\n%s\nGot:\n%s", output, buffer.String())
+	}
+}