Statefulset 滚动升级实现

type ControllerRevision struct {
	metav1.TypeMeta `json:",inline"`
	metav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"`
	// pod spec template的序列化
	Data runtime.RawExtension `json:"data,omitempty" protobuf:"bytes,2,opt,name=data"`
    // Data字段所代表的template的版本号，这个是递增的字段，如果我们修改了sts的pod template，会产生一个新的controllerrevision，
    // 该字段也会递增1
	Revision int64 `json:"revision" protobuf:"varint,3,opt,name=revision"`
}

func (ssc *defaultStatefulSetControl) getStatefulSetRevisions(
	set *apps.StatefulSet,
	revisions []*apps.ControllerRevision) (*apps.ControllerRevision, *apps.ControllerRevision, int32, error) {
	var currentRevision, updateRevision *apps.ControllerRevision

    // 将所有的ControllerRevision按照Revision字段升序排列
	revisionCount := len(revisions)
	history.SortControllerRevisions(revisions)
    // CollisionCount这个字段还不是很清楚
	var collisionCount int32
	if set.Status.CollisionCount != nil {
		collisionCount = *set.Status.CollisionCount
	}

    // 根据当前sts的pod template生成一个新的Revision。其中nextRevision是根据当前最大的revision id来
    // 生成下一个id，生成Revision的过程比较细节，可以先简单理解为对原来template的json.Marshal
	updateRevision, err := newRevision(set, nextRevision(revisions), &collisionCount)
	if err != nil {
		return nil, nil, collisionCount, err
	}

	// 寻找相等的Revision，如果对template进行了更新，是不存在相等的Revision
	equalRevisions := history.FindEqualRevisions(revisions, updateRevision)
	equalCount := len(equalRevisions)

	if equalCount > 0 && history.EqualRevision(revisions[revisionCount-1], equalRevisions[equalCount-1]) {
        // if the equivalent revision is immediately prior the update revision has not changed
        // 什么都没有更新
		updateRevision = revisions[revisionCount-1]
	} else if equalCount > 0 {
		// if the equivalent revision is not immediately prior we will roll back by incrementing the
        // Revision of the equivalent revision
        // 执行的是回滚操作，把当前template修改成跟之前某一个一样，把之前那个ControllerRevision的Revision字段设置成最新
        // 也就是值updateRevision.Revision，执行的是update字段
		updateRevision, err = ssc.controllerHistory.UpdateControllerRevision(
			equalRevisions[equalCount-1],
			updateRevision.Revision)
		if err != nil {
			return nil, nil, collisionCount, err
		}
	} else {
        //if there is no equivalent revision we create a new one
        // 进行了update操作，创建一个新的ControllerRevision
		updateRevision, err = ssc.controllerHistory.CreateControllerRevision(set, updateRevision, &collisionCount)
		if err != nil {
			return nil, nil, collisionCount, err
		}
	}

    // attempt to find the revision that corresponds to the current revision
    // 遍历CurrentRevision，寻找等于set的Status字段中的CurrentRevision
	for i := range revisions {
		if revisions[i].Name == set.Status.CurrentRevision {
			currentRevision = revisions[i]
			break
		}
	}

	// 如果没有currentRevision，设置为updateRevision
	if currentRevision == nil {
		currentRevision = updateRevision
	}
	return currentRevision, updateRevision, collisionCount, nil
}

func (ssc *defaultStatefulSetControl) updateStatefulSet(
	set *apps.StatefulSet,
	currentRevision *apps.ControllerRevision,
	updateRevision *apps.ControllerRevision,
	collisionCount int32,
	pods []*v1.Pod) (*apps.StatefulSetStatus, error) {

// we terminate the Pod with the largest ordinal that does not match the update revision.
for target := len(replicas) - 1; target >= updateMin; target-- {

	// delete the Pod if it is not already terminating and does not match the update revision.
	if getPodRevision(replicas[target]) != updateRevision.Name && !isTerminating(replicas[target]) {
		klog.V(2).Infof("StatefulSet %s/%s terminating Pod %s for update",
			set.Namespace,
			set.Name,
			replicas[target].Name)
		err := ssc.podControl.DeleteStatefulPod(set, replicas[target])
		status.CurrentReplicas--
		return &status, err
	}

	// wait for unhealthy Pods on update
	if !isHealthy(replicas[target]) {
		klog.V(4).Infof(
			"StatefulSet %s/%s is waiting for Pod %s to update",
			set.Namespace,
			set.Name,
			replicas[target].Name)
		return &status, nil
	}

}