k3s/pkg/controller/deployment/sync.go

/*
Copyright 2016 The Kubernetes Authors.

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 deployment

import (
	"fmt"
	"reflect"
	"sort"
	"strconv"

	"github.com/golang/glog"
	"k8s.io/kubernetes/pkg/api"
	"k8s.io/kubernetes/pkg/api/errors"
	"k8s.io/kubernetes/pkg/api/unversioned"
	"k8s.io/kubernetes/pkg/apis/extensions"
	"k8s.io/kubernetes/pkg/controller"
	deploymentutil "k8s.io/kubernetes/pkg/controller/deployment/util"
	utilerrors "k8s.io/kubernetes/pkg/util/errors"
	labelsutil "k8s.io/kubernetes/pkg/util/labels"
	podutil "k8s.io/kubernetes/pkg/util/pod"
	rsutil "k8s.io/kubernetes/pkg/util/replicaset"
)

// syncStatusOnly only updates Deployments Status and doesn't take any mutating actions.
func (dc *DeploymentController) syncStatusOnly(deployment *extensions.Deployment) error {
	newRS, oldRSs, err := dc.getAllReplicaSetsAndSyncRevision(deployment, false)
	if err != nil {
		return err
	}

	allRSs := append(oldRSs, newRS)
	return dc.syncDeploymentStatus(allRSs, newRS, deployment)
}

// sync is responsible for reconciling deployments on scaling events or when they
// are paused.
func (dc *DeploymentController) sync(deployment *extensions.Deployment) error {
	newRS, oldRSs, err := dc.getAllReplicaSetsAndSyncRevision(deployment, false)
	if err != nil {
		return err
	}
	if err := dc.scale(deployment, newRS, oldRSs); err != nil {
		// If we get an error while trying to scale, the deployment will be requeued
		// so we can abort this resync
		return err
	}
	dc.cleanupDeployment(oldRSs, deployment)

	allRSs := append(oldRSs, newRS)
	return dc.syncDeploymentStatus(allRSs, newRS, deployment)
}

// getAllReplicaSetsAndSyncRevision returns all the replica sets for the provided deployment (new and all old), with new RS's and deployment's revision updated.
// 1. Get all old RSes this deployment targets, and calculate the max revision number among them (maxOldV).
// 2. Get new RS this deployment targets (whose pod template matches deployment's), and update new RS's revision number to (maxOldV + 1),
//    only if its revision number is smaller than (maxOldV + 1). If this step failed, we'll update it in the next deployment sync loop.
// 3. Copy new RS's revision number to deployment (update deployment's revision). If this step failed, we'll update it in the next deployment sync loop.
// Note that currently the deployment controller is using caches to avoid querying the server for reads.
// This may lead to stale reads of replica sets, thus incorrect deployment status.
func (dc *DeploymentController) getAllReplicaSetsAndSyncRevision(deployment *extensions.Deployment, createIfNotExisted bool) (*extensions.ReplicaSet, []*extensions.ReplicaSet, error) {
	// List the deployment's RSes & Pods and apply pod-template-hash info to deployment's adopted RSes/Pods
	rsList, podList, err := dc.rsAndPodsWithHashKeySynced(deployment)
	if err != nil {
		return nil, nil, fmt.Errorf("error labeling replica sets and pods with pod-template-hash: %v", err)
	}
	_, allOldRSs, err := deploymentutil.FindOldReplicaSets(deployment, rsList, podList)
	if err != nil {
		return nil, nil, err
	}

	// Get new replica set with the updated revision number
	newRS, err := dc.getNewReplicaSet(deployment, rsList, allOldRSs, createIfNotExisted)
	if err != nil {
		return nil, nil, err
	}

	return newRS, allOldRSs, nil
}

// rsAndPodsWithHashKeySynced returns the RSes and pods the given deployment targets, with pod-template-hash information synced.
func (dc *DeploymentController) rsAndPodsWithHashKeySynced(deployment *extensions.Deployment) ([]*extensions.ReplicaSet, *api.PodList, error) {
	rsList, err := deploymentutil.ListReplicaSets(deployment,
		func(namespace string, options api.ListOptions) ([]*extensions.ReplicaSet, error) {
			return dc.rsLister.ReplicaSets(namespace).List(options.LabelSelector)
		})
	if err != nil {
		return nil, nil, fmt.Errorf("error listing ReplicaSets: %v", err)
	}
	syncedRSList := []*extensions.ReplicaSet{}
	for _, rs := range rsList {
		// Add pod-template-hash information if it's not in the RS.
		// Otherwise, new RS produced by Deployment will overlap with pre-existing ones
		// that aren't constrained by the pod-template-hash.
		syncedRS, err := dc.addHashKeyToRSAndPods(rs)
		if err != nil {
			return nil, nil, err
		}
		syncedRSList = append(syncedRSList, syncedRS)
	}
	syncedPodList, err := dc.listPods(deployment)
	if err != nil {
		return nil, nil, err
	}
	return syncedRSList, syncedPodList, nil
}

// addHashKeyToRSAndPods adds pod-template-hash information to the given rs, if it's not already there, with the following steps:
// 1. Add hash label to the rs's pod template, and make sure the controller sees this update so that no orphaned pods will be created
// 2. Add hash label to all pods this rs owns, wait until replicaset controller reports rs.Status.FullyLabeledReplicas equal to the desired number of replicas
// 3. Add hash label to the rs's label and selector
func (dc *DeploymentController) addHashKeyToRSAndPods(rs *extensions.ReplicaSet) (updatedRS *extensions.ReplicaSet, err error) {
	objCopy, err := api.Scheme.Copy(rs)
	if err != nil {
		return nil, err
	}
	updatedRS = objCopy.(*extensions.ReplicaSet)

	// If the rs already has the new hash label in its selector, it's done syncing
	if labelsutil.SelectorHasLabel(rs.Spec.Selector, extensions.DefaultDeploymentUniqueLabelKey) {
		return
	}
	namespace := rs.Namespace
	hash := rsutil.GetPodTemplateSpecHash(rs)
	rsUpdated := false
	// 1. Add hash template label to the rs. This ensures that any newly created pods will have the new label.
	updatedRS, rsUpdated, err = rsutil.UpdateRSWithRetries(dc.client.Extensions().ReplicaSets(namespace), updatedRS,
		func(updated *extensions.ReplicaSet) error {
			// Precondition: the RS doesn't contain the new hash in its pod template label.
			if updated.Spec.Template.Labels[extensions.DefaultDeploymentUniqueLabelKey] == hash {
				return utilerrors.ErrPreconditionViolated
			}
			updated.Spec.Template.Labels = labelsutil.AddLabel(updated.Spec.Template.Labels, extensions.DefaultDeploymentUniqueLabelKey, hash)
			return nil
		})
	if err != nil {
		return nil, fmt.Errorf("error updating %s %s/%s pod template label with template hash: %v", updatedRS.Kind, updatedRS.Namespace, updatedRS.Name, err)
	}
	if !rsUpdated {
		// If RS wasn't updated but didn't return error in step 1, we've hit a RS not found error.
		// Return here and retry in the next sync loop.
		return rs, nil
	}
	// Make sure rs pod template is updated so that it won't create pods without the new label (orphaned pods).
	if updatedRS.Generation > updatedRS.Status.ObservedGeneration {
		if err = deploymentutil.WaitForReplicaSetUpdated(dc.client, updatedRS.Generation, namespace, updatedRS.Name); err != nil {
			return nil, fmt.Errorf("error waiting for %s %s/%s generation %d observed by controller: %v", updatedRS.Kind, updatedRS.Namespace, updatedRS.Name, updatedRS.Generation, err)
		}
	}
	glog.V(4).Infof("Observed the update of %s %s/%s's pod template with hash %s.", rs.Kind, rs.Namespace, rs.Name, hash)

	// 2. Update all pods managed by the rs to have the new hash label, so they will be correctly adopted.
	selector, err := unversioned.LabelSelectorAsSelector(updatedRS.Spec.Selector)
	if err != nil {
		return nil, fmt.Errorf("error in converting selector to label selector for replica set %s: %s", updatedRS.Name, err)
	}
	options := api.ListOptions{LabelSelector: selector}
	pods, err := dc.podLister.Pods(namespace).List(options.LabelSelector)
	if err != nil {
		return nil, fmt.Errorf("error in getting pod list for namespace %s and list options %+v: %s", namespace, options, err)
	}
	podList := api.PodList{Items: make([]api.Pod, 0, len(pods))}
	for i := range pods {
		podList.Items = append(podList.Items, *pods[i])
	}
	allPodsLabeled := false
	if allPodsLabeled, err = deploymentutil.LabelPodsWithHash(&podList, updatedRS, dc.client, namespace, hash); err != nil {
		return nil, fmt.Errorf("error in adding template hash label %s to pods %+v: %s", hash, podList, err)
	}
	// If not all pods are labeled but didn't return error in step 2, we've hit at least one pod not found error.
	// Return here and retry in the next sync loop.
	if !allPodsLabeled {
		return updatedRS, nil
	}

	// We need to wait for the replicaset controller to observe the pods being
	// labeled with pod template hash. Because previously we've called
	// WaitForReplicaSetUpdated, the replicaset controller should have dropped
	// FullyLabeledReplicas to 0 already, we only need to wait it to increase
	// back to the number of replicas in the spec.
	if err = deploymentutil.WaitForPodsHashPopulated(dc.client, updatedRS.Generation, namespace, updatedRS.Name); err != nil {
		return nil, fmt.Errorf("%s %s/%s: error waiting for replicaset controller to observe pods being labeled with template hash: %v", updatedRS.Kind, updatedRS.Namespace, updatedRS.Name, err)
	}

	// 3. Update rs label and selector to include the new hash label
	// Copy the old selector, so that we can scrub out any orphaned pods
	if updatedRS, rsUpdated, err = rsutil.UpdateRSWithRetries(dc.client.Extensions().ReplicaSets(namespace), updatedRS,
		func(updated *extensions.ReplicaSet) error {
			// Precondition: the RS doesn't contain the new hash in its label or selector.
			if updated.Labels[extensions.DefaultDeploymentUniqueLabelKey] == hash && updated.Spec.Selector.MatchLabels[extensions.DefaultDeploymentUniqueLabelKey] == hash {
				return utilerrors.ErrPreconditionViolated
			}
			updated.Labels = labelsutil.AddLabel(updated.Labels, extensions.DefaultDeploymentUniqueLabelKey, hash)
			updated.Spec.Selector = labelsutil.AddLabelToSelector(updated.Spec.Selector, extensions.DefaultDeploymentUniqueLabelKey, hash)
			return nil
		}); err != nil {
		return nil, fmt.Errorf("error updating %s %s/%s label and selector with template hash: %v", updatedRS.Kind, updatedRS.Namespace, updatedRS.Name, err)
	}
	if rsUpdated {
		glog.V(4).Infof("Updated %s %s/%s's selector and label with hash %s.", rs.Kind, rs.Namespace, rs.Name, hash)
	}
	// If the RS isn't actually updated in step 3, that's okay, we'll retry in the next sync loop since its selector isn't updated yet.

	// TODO: look for orphaned pods and label them in the background somewhere else periodically

	return updatedRS, nil
}

func (dc *DeploymentController) listPods(deployment *extensions.Deployment) (*api.PodList, error) {
	return deploymentutil.ListPods(deployment,
		func(namespace string, options api.ListOptions) (*api.PodList, error) {
			pods, err := dc.podLister.Pods(namespace).List(options.LabelSelector)
			result := api.PodList{Items: make([]api.Pod, 0, len(pods))}
			for i := range pods {
				result.Items = append(result.Items, *pods[i])
			}
			return &result, err
		})
}

// Returns a replica set that matches the intent of the given deployment. Returns nil if the new replica set doesn't exist yet.
// 1. Get existing new RS (the RS that the given deployment targets, whose pod template is the same as deployment's).
// 2. If there's existing new RS, update its revision number if it's smaller than (maxOldRevision + 1), where maxOldRevision is the max revision number among all old RSes.
// 3. If there's no existing new RS and createIfNotExisted is true, create one with appropriate revision number (maxOldRevision + 1) and replicas.
// Note that the pod-template-hash will be added to adopted RSes and pods.
func (dc *DeploymentController) getNewReplicaSet(deployment *extensions.Deployment, rsList, oldRSs []*extensions.ReplicaSet, createIfNotExisted bool) (*extensions.ReplicaSet, error) {
	existingNewRS, err := deploymentutil.FindNewReplicaSet(deployment, rsList)
	if err != nil {
		return nil, err
	}

	// Calculate the max revision number among all old RSes
	maxOldRevision := deploymentutil.MaxRevision(oldRSs)
	// Calculate revision number for this new replica set
	newRevision := strconv.FormatInt(maxOldRevision+1, 10)

	// Latest replica set exists. We need to sync its annotations (includes copying all but
	// annotationsToSkip from the parent deployment, and update revision, desiredReplicas,
	// and maxReplicas) and also update the revision annotation in the deployment with the
	// latest revision.
	if existingNewRS != nil {
		objCopy, err := api.Scheme.Copy(existingNewRS)
		if err != nil {
			return nil, err
		}
		rsCopy := objCopy.(*extensions.ReplicaSet)

		// Set existing new replica set's annotation
		annotationsUpdated := deploymentutil.SetNewReplicaSetAnnotations(deployment, rsCopy, newRevision, true)
		minReadySecondsNeedsUpdate := rsCopy.Spec.MinReadySeconds != deployment.Spec.MinReadySeconds
		if annotationsUpdated || minReadySecondsNeedsUpdate {
			rsCopy.Spec.MinReadySeconds = deployment.Spec.MinReadySeconds
			return dc.client.Extensions().ReplicaSets(rsCopy.ObjectMeta.Namespace).Update(rsCopy)
		}

		updateConditions := deploymentutil.SetDeploymentRevision(deployment, newRevision)

		if updateConditions {
			if deployment, err = dc.client.Extensions().Deployments(deployment.Namespace).UpdateStatus(deployment); err != nil {
				return nil, err
			}
		}
		return rsCopy, nil
	}

	if !createIfNotExisted {
		return nil, nil
	}

	// new ReplicaSet does not exist, create one.
	namespace := deployment.Namespace
	podTemplateSpecHash := podutil.GetPodTemplateSpecHash(deployment.Spec.Template)
	newRSTemplate := deploymentutil.GetNewReplicaSetTemplate(deployment)
	// Add podTemplateHash label to selector.
	newRSSelector := labelsutil.CloneSelectorAndAddLabel(deployment.Spec.Selector, extensions.DefaultDeploymentUniqueLabelKey, podTemplateSpecHash)

	// Create new ReplicaSet
	newRS := extensions.ReplicaSet{
		ObjectMeta: api.ObjectMeta{
			// Make the name deterministic, to ensure idempotence
			Name:      deployment.Name + "-" + fmt.Sprintf("%d", podTemplateSpecHash),
			Namespace: namespace,
		},
		Spec: extensions.ReplicaSetSpec{
			Replicas:        0,
			MinReadySeconds: deployment.Spec.MinReadySeconds,
			Selector:        newRSSelector,
			Template:        newRSTemplate,
		},
	}
	allRSs := append(oldRSs, &newRS)
	newReplicasCount, err := deploymentutil.NewRSNewReplicas(deployment, allRSs, &newRS)
	if err != nil {
		return nil, err
	}

	newRS.Spec.Replicas = newReplicasCount
	// Set new replica set's annotation
	deploymentutil.SetNewReplicaSetAnnotations(deployment, &newRS, newRevision, false)
	createdRS, err := dc.client.Extensions().ReplicaSets(namespace).Create(&newRS)
	if err != nil {
		return nil, fmt.Errorf("error creating replica set %v: %v", deployment.Name, err)
	}
	if newReplicasCount > 0 {
		dc.eventRecorder.Eventf(deployment, api.EventTypeNormal, "ScalingReplicaSet", "Scaled %s replica set %s to %d", "up", createdRS.Name, newReplicasCount)
	}

	deploymentutil.SetDeploymentRevision(deployment, newRevision)
	_, err = dc.client.Extensions().Deployments(deployment.Namespace).UpdateStatus(deployment)
	return createdRS, err
}

// scale scales proportionally in order to mitigate risk. Otherwise, scaling up can increase the size
// of the new replica set and scaling down can decrease the sizes of the old ones, both of which would
// have the effect of hastening the rollout progress, which could produce a higher proportion of unavailable
// replicas in the event of a problem with the rolled out template. Should run only on scaling events or
// when a deployment is paused and not during the normal rollout process.
func (dc *DeploymentController) scale(deployment *extensions.Deployment, newRS *extensions.ReplicaSet, oldRSs []*extensions.ReplicaSet) error {
	// If there is only one active replica set then we should scale that up to the full count of the
	// deployment. If there is no active replica set, then we should scale up the newest replica set.
	if activeOrLatest := deploymentutil.FindActiveOrLatest(newRS, oldRSs); activeOrLatest != nil {
		if activeOrLatest.Spec.Replicas == deployment.Spec.Replicas {
			return nil
		}
		_, _, err := dc.scaleReplicaSetAndRecordEvent(activeOrLatest, deployment.Spec.Replicas, deployment)
		return err
	}

	// If the new replica set is saturated, old replica sets should be fully scaled down.
	// This case handles replica set adoption during a saturated new replica set.
	if deploymentutil.IsSaturated(deployment, newRS) {
		for _, old := range controller.FilterActiveReplicaSets(oldRSs) {
			if _, _, err := dc.scaleReplicaSetAndRecordEvent(old, 0, deployment); err != nil {
				return err
			}
		}
		return nil
	}

	// There are old replica sets with pods and the new replica set is not saturated.
	// We need to proportionally scale all replica sets (new and old) in case of a
	// rolling deployment.
	if deploymentutil.IsRollingUpdate(deployment) {
		allRSs := controller.FilterActiveReplicaSets(append(oldRSs, newRS))
		allRSsReplicas := deploymentutil.GetReplicaCountForReplicaSets(allRSs)

		allowedSize := int32(0)
		if deployment.Spec.Replicas > 0 {
			allowedSize = deployment.Spec.Replicas + deploymentutil.MaxSurge(*deployment)
		}

		// Number of additional replicas that can be either added or removed from the total
		// replicas count. These replicas should be distributed proportionally to the active
		// replica sets.
		deploymentReplicasToAdd := allowedSize - allRSsReplicas

		// The additional replicas should be distributed proportionally amongst the active
		// replica sets from the larger to the smaller in size replica set. Scaling direction
		// drives what happens in case we are trying to scale replica sets of the same size.
		// In such a case when scaling up, we should scale up newer replica sets first, and
		// when scaling down, we should scale down older replica sets first.
		scalingOperation := "up"
		switch {
		case deploymentReplicasToAdd > 0:
			sort.Sort(controller.ReplicaSetsBySizeNewer(allRSs))

		case deploymentReplicasToAdd < 0:
			sort.Sort(controller.ReplicaSetsBySizeOlder(allRSs))
			scalingOperation = "down"

		default: /* deploymentReplicasToAdd == 0 */
			// Nothing to add.
			return nil
		}

		// Iterate over all active replica sets and estimate proportions for each of them.
		// The absolute value of deploymentReplicasAdded should never exceed the absolute
		// value of deploymentReplicasToAdd.
		deploymentReplicasAdded := int32(0)
		for i := range allRSs {
			rs := allRSs[i]

			proportion := deploymentutil.GetProportion(rs, *deployment, deploymentReplicasToAdd, deploymentReplicasAdded)

			rs.Spec.Replicas += proportion
			deploymentReplicasAdded += proportion
		}

		// Update all replica sets
		for i := range allRSs {
			rs := allRSs[i]

			// Add/remove any leftovers to the largest replica set.
			if i == 0 {
				leftover := deploymentReplicasToAdd - deploymentReplicasAdded
				rs.Spec.Replicas += leftover
				if rs.Spec.Replicas < 0 {
					rs.Spec.Replicas = 0
				}
			}

			if _, err := dc.scaleReplicaSet(rs, rs.Spec.Replicas, deployment, scalingOperation); err != nil {
				// Return as soon as we fail, the deployment is requeued
				return err
			}
		}
	}
	return nil
}

func (dc *DeploymentController) scaleReplicaSetAndRecordEvent(rs *extensions.ReplicaSet, newScale int32, deployment *extensions.Deployment) (bool, *extensions.ReplicaSet, error) {
	// No need to scale
	if rs.Spec.Replicas == newScale {
		return false, rs, nil
	}
	var scalingOperation string
	if rs.Spec.Replicas < newScale {
		scalingOperation = "up"
	} else {
		scalingOperation = "down"
	}
	newRS, err := dc.scaleReplicaSet(rs, newScale, deployment, scalingOperation)
	return true, newRS, err
}

func (dc *DeploymentController) scaleReplicaSet(rs *extensions.ReplicaSet, newScale int32, deployment *extensions.Deployment, scalingOperation string) (*extensions.ReplicaSet, error) {
	// NOTE: This mutates the ReplicaSet passed in. Not sure if that's a good idea.
	rs.Spec.Replicas = newScale
	deploymentutil.SetReplicasAnnotations(rs, deployment.Spec.Replicas, deployment.Spec.Replicas+deploymentutil.MaxSurge(*deployment))
	rs, err := dc.client.Extensions().ReplicaSets(rs.Namespace).Update(rs)
	if err == nil {
		dc.eventRecorder.Eventf(deployment, api.EventTypeNormal, "ScalingReplicaSet", "Scaled %s replica set %s to %d", scalingOperation, rs.Name, newScale)
	}
	return rs, err
}

// cleanupDeployment is responsible for cleaning up a deployment ie. retains all but the latest N old replica sets
// where N=d.Spec.RevisionHistoryLimit. Old replica sets are older versions of the podtemplate of a deployment kept
// around by default 1) for historical reasons and 2) for the ability to rollback a deployment.
func (dc *DeploymentController) cleanupDeployment(oldRSs []*extensions.ReplicaSet, deployment *extensions.Deployment) error {
	if deployment.Spec.RevisionHistoryLimit == nil {
		return nil
	}
	diff := int32(len(oldRSs)) - *deployment.Spec.RevisionHistoryLimit
	if diff <= 0 {
		return nil
	}

	sort.Sort(controller.ReplicaSetsByCreationTimestamp(oldRSs))

	var errList []error
	// TODO: This should be parallelized.
	for i := int32(0); i < diff; i++ {
		rs := oldRSs[i]
		// Avoid delete replica set with non-zero replica counts
		if rs.Status.Replicas != 0 || rs.Spec.Replicas != 0 || rs.Generation > rs.Status.ObservedGeneration {
			continue
		}
		if err := dc.client.Extensions().ReplicaSets(rs.Namespace).Delete(rs.Name, nil); err != nil && !errors.IsNotFound(err) {
			glog.V(2).Infof("Failed deleting old replica set %v for deployment %v: %v", rs.Name, deployment.Name, err)
			errList = append(errList, err)
		}
	}

	return utilerrors.NewAggregate(errList)
}

// syncDeploymentStatus checks if the status is up-to-date and sync it if necessary
func (dc *DeploymentController) syncDeploymentStatus(allRSs []*extensions.ReplicaSet, newRS *extensions.ReplicaSet, d *extensions.Deployment) error {
	newStatus := dc.calculateStatus(allRSs, newRS, d)

	if reflect.DeepEqual(d.Status, newStatus) {
		return nil
	}

	newDeployment := d
	newDeployment.Status = newStatus
	_, err := dc.client.Extensions().Deployments(newDeployment.Namespace).UpdateStatus(newDeployment)
	return err
}

func (dc *DeploymentController) calculateStatus(allRSs []*extensions.ReplicaSet, newRS *extensions.ReplicaSet, deployment *extensions.Deployment) extensions.DeploymentStatus {
	availableReplicas := deploymentutil.GetAvailableReplicaCountForReplicaSets(allRSs)
	totalReplicas := deploymentutil.GetReplicaCountForReplicaSets(allRSs)

	return extensions.DeploymentStatus{
		// TODO: Ensure that if we start retrying status updates, we won't pick up a new Generation value.
		ObservedGeneration:  deployment.Generation,
		Replicas:            deploymentutil.GetActualReplicaCountForReplicaSets(allRSs),
		UpdatedReplicas:     deploymentutil.GetActualReplicaCountForReplicaSets([]*extensions.ReplicaSet{newRS}),
		AvailableReplicas:   availableReplicas,
		UnavailableReplicas: totalReplicas - availableReplicas,
	}
}

// isScalingEvent checks whether the provided deployment has been updated with a scaling event
// by looking at the desired-replicas annotation in the active replica sets of the deployment.
func (dc *DeploymentController) isScalingEvent(d *extensions.Deployment) (bool, error) {
	newRS, oldRSs, err := dc.getAllReplicaSetsAndSyncRevision(d, false)
	if err != nil {
		return false, err
	}
	allRSs := append(oldRSs, newRS)
	for _, rs := range controller.FilterActiveReplicaSets(allRSs) {
		desired, ok := deploymentutil.GetDesiredReplicasAnnotation(rs)
		if !ok {
			continue
		}
		if desired != d.Spec.Replicas {
			return true, nil
		}
	}
	return false, nil
}