Pod调度失败了还有机会吗？
在 k8s 中一个Pod由于某些原因调度失败后，会被放入调度失败队列，这个队列里面的Pod后面都怎么样了呢？他们怎么样才能重新获取到”重新做人的机会“呢？这篇文章，我们从源码的角度来看看来龙去脉
在 k8s 中会起两个协程，定期把 backoffQ 和 unscheduledQ 里面的 Pod拿到activeQ里面去
func (p *PriorityQueue) Run() {
go wait.Until(p.flushBackoffQCompleted, 1.0*time.Second, p.stop)
go wait.Until(p.flushUnschedulablePodsLeftover, 30*time.Second, p.stop)
}
flushUnschedulablePodsLeftover
func (p *PriorityQueue) flushUnschedulablePodsLeftover() {
p.lock.Lock()
defer p.lock.Unlock()
var podsToMove []*framework.QueuedPodInfo
currentTime := p.clock.Now()
for _, pInfo := range p.unschedulablePods.podInfoMap {
lastScheduleTime := pInfo.Timestamp
if currentTime.Sub(lastScheduleTime) > p.podMaxInUnschedulablePodsDuration {
podsToMove = append(podsToMove, pInfo)
}
}
if len(podsToMove) > 0 {
p.movePodsToActiveOrBackoffQueue(podsToMove, UnschedulableTimeout)
}
}
func (p *PriorityQueue) movePodsToActiveOrBackoffQueue(podInfoList []*framework.QueuedPodInfo, event framework.ClusterEvent) {
activated := false
for _, pInfo := range podInfoList {
// If the event doesn't help making the Pod schedulable, continue.
// Note: we don't run the check if pInfo.UnschedulablePlugins is nil, which denotes
// either there is some abnormal error, or scheduling the pod failed by plugins other than PreFilter, Filter and Permit.
// In that case, it's desired to move it anyways.
if len(pInfo.UnschedulablePlugins) != 0 && !p.podMatchesEvent(pInfo, event) {
continue
}
pod := pInfo.Pod
if p.isPodBackingoff(pInfo) {
if err := p.podBackoffQ.Add(pInfo); err != nil {
klog.ErrorS(err, "Error adding pod to the backoff queue", "pod", klog.KObj(pod))
} else {
metrics.SchedulerQueueIncomingPods.WithLabelValues("backoff", event.Label).Inc()
p.unschedulablePods.delete(pod)
}
} else {
if err := p.activeQ.Add(pInfo); err != nil {
klog.ErrorS(err, "Error adding pod to the scheduling queue", "pod", klog.KObj(pod))
} else {
metrics.SchedulerQueueIncomingPods.WithLabelValues("active", event.Label).Inc()
p.unschedulablePods.delete(pod)
}
}
}
p.moveRequestCycle = p.schedulingCycle
if activated {
p.cond.Broadcast()
}
}
将在unscheduledQ里面停留时长超过podMaxInUnschedulablePodsDuration（默认是5min）的pod放入到 ActiveQ 或 BackoffQueue，具体是放到哪个队列里面，根据下面规则判断：
根据这个Pod尝试被调度的次数，计算这个Pod应该等待下一次调度的时间，计算规则为指数级增长，即按照1s,2s,4s,8s这样的时间进行等待，但是这个等待时间也不会无限增加，会受到 podMaxBackoffDuration（默认10s） 的限制，这个参数的意思是一个 Pod处于Backoff的最大时间，如果等待的时间如果超过了 podMaxBackoffDuration，那么就只等待 podMaxBackoffDuration 就会再次被调度；
当前时间 - 上次调度的时间 > 根据1获取到的应该等待的时间，那么就把Pod放到activeQ里面，将会被调度，否则Pod被放入 backoff 队列里继续等待，如果是在backoff 队列等待的话，后面就会被flushBackoffQCompleted取出
所以这里 Pod 如果满足条件的话 就一定会从unscheduleQ里面移到 backooff里面或者activeQ里面
flushBackoffQCompleted
去取 backoff 队列（优先队列）里面取等待时间结束的 Pod，放入 activeQ
func (p *PriorityQueue) flushBackoffQCompleted() {
p.lock.Lock()
defer p.lock.Unlock()
activated := false
for {
rawPodInfo := p.podBackoffQ.Peek()
if rawPodInfo == nil {
break
}
pod := rawPodInfo.(*framework.QueuedPodInfo).Pod
boTime := p.getBackoffTime(rawPodInfo.(*framework.QueuedPodInfo))
if boTime.After(p.clock.Now()) {
break
}
_, err := p.podBackoffQ.Pop()
if err != nil {
klog.ErrorS(err, "Unable to pop pod from backoff queue despite backoff completion", "pod", klog.KObj(pod))
break
}
p.activeQ.Add(rawPodInfo)
metrics.SchedulerQueueIncomingPods.WithLabelValues("active", BackoffComplete).Inc()
activated = true
}
if activated {
p.cond.Broadcast()
}
}那么除了上述定期主动去判断一个 UnscheduledQ 或 backoffQ 里面的Pod是不是可以再次被调度，那么还有没有其他情况呢？
答案是有的。
还有四种情况会重新判断这两个队列里的 Pod 是不是要重新调度
- 有新节点加入集群
- 节点配置或状态发生变化
- 已经存在的 Pod 发生变化
- 集群内有Pod被删除
informerFactory.Core().V1().Nodes().Informer().AddEventHandler(
cache.ResourceEventHandlerFuncs{
AddFunc: sched.addNodeToCache,
UpdateFunc: sched.updateNodeInCache,
DeleteFunc: sched.deleteNodeFromCache,
},
)
新加入节点
func (sched *Scheduler) addNodeToCache(obj interface{}) {
node, ok := obj.(*v1.Node)
if !ok {
klog.ErrorS(nil, "Cannot convert to *v1.Node", "obj", obj)
return
}
nodeInfo := sched.Cache.AddNode(node)
klog.V(3).InfoS("Add event for node", "node", klog.KObj(node))
sched.SchedulingQueue.MoveAllToActiveOrBackoffQueue(queue.NodeAdd, preCheckForNode(nodeInfo))
}
func preCheckForNode(nodeInfo *framework.NodeInfo) queue.PreEnqueueCheck {
// Note: the following checks doesn't take preemption into considerations, in very rare
// cases (e.g., node resizing), "pod" may still fail a check but preemption helps. We deliberately
// chose to ignore those cases as unschedulable pods will be re-queued eventually.
return func(pod *v1.Pod) bool {
admissionResults := AdmissionCheck(pod, nodeInfo, false)
if len(admissionResults) != 0 {
return false
}
_, isUntolerated := corev1helpers.FindMatchingUntoleratedTaint(nodeInfo.Node().Spec.Taints, pod.Spec.Tolerations, func(t *v1.Taint) bool {
return t.Effect == v1.TaintEffectNoSchedule
})
return !isUntolerated
}
}
可以看到，当有节点加入集群的时候，会把unscheduledQ 里面的Pod 依次拿出来做下面的判断：
- Pod 对 节点的亲和性
- Pod 中 Nodename不为空 那么判断新加入节点的Name判断pod Nodename是否相等
- 判断 Pod 中容器对端口的要求是否和新加入节点已经被使用的端口冲突
- Pod 是否容忍了Node的Pod
只有上述4个条件都满足，那么新加入节点这个事件才会触发这个未被调度的Pod加入到 backoffQ 或者 activeQ，至于是加入哪个queue，上面已经分析过了
节点更新
func (sched *Scheduler) updateNodeInCache(oldObj, newObj interface{}) {
oldNode, ok := oldObj.(*v1.Node)
if !ok {
klog.ErrorS(nil, "Cannot convert oldObj to *v1.Node", "oldObj", oldObj)
return
}
newNode, ok := newObj.(*v1.Node)
if !ok {
klog.ErrorS(nil, "Cannot convert newObj to *v1.Node", "newObj", newObj)
return
}
nodeInfo := sched.Cache.UpdateNode(oldNode, newNode)
// Only requeue unschedulable pods if the node became more schedulable.
if event := nodeSchedulingPropertiesChange(newNode, oldNode); event != nil {
sched.SchedulingQueue.MoveAllToActiveOrBackoffQueue(*event, preCheckForNode(nodeInfo))
}
}func nodeSchedulingPropertiesChange(newNode *v1.Node, oldNode *v1.Node) *framework.ClusterEvent {
if nodeSpecUnschedulableChanged(newNode, oldNode) {
return &queue.NodeSpecUnschedulableChange
}
if nodeAllocatableChanged(newNode, oldNode) {
return &queue.NodeAllocatableChange
}
if nodeLabelsChanged(newNode, oldNode) {
return &queue.NodeLabelChange
}
if nodeTaintsChanged(newNode, oldNode) {
return &queue.NodeTaintChange
}
if nodeConditionsChanged(newNode, oldNode) {
return &queue.NodeConditionChange
}
return nil
}
首先是判断节点是何种配置发生了变化，有如下情况
- 节点可调度情况发生变化
- 节点可分配资源发生变化
- 节点标签发生变化
- 节点污点发生变化
- 节点状态发生变化
如果某个 Pod 调度失败的原因可以匹配到上面其中一个原因，那么节点更新这个事件才会触发这个未被调度的Pod加入到 backoffQ 或者 activeQ
informerFactory.Core().V1().Pods().Informer().AddEventHandler(
cache.FilteringResourceEventHandler{
FilterFunc: func(obj interface{}) bool {
switch t := obj.(type) {
case *v1.Pod:
return assignedPod(t)
case cache.DeletedFinalStateUnknown:
if _, ok := t.Obj.(*v1.Pod); ok {
// The carried object may be stale, so we don't use it to check if
// it's assigned or not. Attempting to cleanup anyways.
return true
}
utilruntime.HandleError(fmt.Errorf("unable to convert object %T to *v1.Pod in %T", obj, sched))
return false
default:
utilruntime.HandleError(fmt.Errorf("unable to handle object in %T: %T", sched, obj))
return false
}
},
Handler: cache.ResourceEventHandlerFuncs{
AddFunc: sched.addPodToCache,
UpdateFunc: sched.updatePodInCache,
DeleteFunc: sched.deletePodFromCache,
},
},
)
已经存在的 Pod 发生变化
func (sched *Scheduler) addPodToCache(obj interface{}) {
pod, ok := obj.(*v1.Pod)
if !ok {
klog.ErrorS(nil, "Cannot convert to *v1.Pod", "obj", obj)
return
}
klog.V(3).InfoS("Add event for scheduled pod", "pod", klog.KObj(pod))
if err := sched.Cache.AddPod(pod); err != nil {
klog.ErrorS(err, "Scheduler cache AddPod failed", "pod", klog.KObj(pod))
}
sched.SchedulingQueue.AssignedPodAdded(pod)
}
func (p *PriorityQueue) AssignedPodAdded(pod *v1.Pod) {
p.lock.Lock()
p.movePodsToActiveOrBackoffQueue(p.getUnschedulablePodsWithMatchingAffinityTerm(pod), AssignedPodAdd)
p.lock.Unlock()
}
func (p *PriorityQueue) getUnschedulablePodsWithMatchingAffinityTerm(pod *v1.Pod) []*framework.QueuedPodInfo {
var nsLabels labels.Set
nsLabels = interpodaffinity.GetNamespaceLabelsSnapshot(pod.Namespace, p.nsLister)
var podsToMove []*framework.QueuedPodInfo
for _, pInfo := range p.unschedulablePods.podInfoMap {
for _, term := range pInfo.RequiredAffinityTerms {
if term.Matches(pod, nsLabels) {
podsToMove = append(podsToMove, pInfo)
break
}
}
}
return podsToMove
}可以看到，已经存在的Pod发生变化后，会把这个Pod亲和性配置依次和unscheduledQ里面的Pod匹配，如果能够匹配上，那么节点更新这个事件才会触发这个未被调度的Pod加入到 backoffQ 或者 activeQ。
集群内有Pod删除
func (sched *Scheduler) deletePodFromCache(obj interface{}) {
var pod *v1.Pod
switch t := obj.(type) {
case *v1.Pod:
pod = t
case cache.DeletedFinalStateUnknown:
var ok bool
pod, ok = t.Obj.(*v1.Pod)
if !ok {
klog.ErrorS(nil, "Cannot convert to *v1.Pod", "obj", t.Obj)
return
}
default:
klog.ErrorS(nil, "Cannot convert to *v1.Pod", "obj", t)
return
}
klog.V(3).InfoS("Delete event for scheduled pod", "pod", klog.KObj(pod))
if err := sched.Cache.RemovePod(pod); err != nil {
klog.ErrorS(err, "Scheduler cache RemovePod failed", "pod", klog.KObj(pod))
}
sched.SchedulingQueue.MoveAllToActiveOrBackoffQueue(queue.AssignedPodDelete, nil)
}
可以看到，Pod删除时间不像其他时间需要做额外的判断，这个preCheck函数是空的，所以所有 unscheduledQ 里面的Pod都会被放到 activeQ或者backoffQ里面。
从上面的情况，我们可以看到，集群内有事件发生变化，是可以加速调度失败的Pod被重新调度的进程的。常规的是，调度失败的 Pod 需要等5min 然后才会被重新加入 backoff 或 activeQ。backoffQ里面的Pod也需要等一段时间才会重新调度。这也就是为什么，当你修改节点配置的时候，能看到Pod马上重新被调度的原因
上面就是一个Pod调度失败后，重新触发调度的所有情况了。
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