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273 lines
11 KiB
Go
273 lines
11 KiB
Go
/*
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Copyright 2017 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package preemption
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import (
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"fmt"
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"math"
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"k8s.io/api/core/v1"
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"k8s.io/client-go/tools/record"
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"k8s.io/klog/v2"
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"k8s.io/kubernetes/pkg/api/v1/resource"
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v1qos "k8s.io/kubernetes/pkg/apis/core/v1/helper/qos"
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"k8s.io/kubernetes/pkg/kubelet/events"
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"k8s.io/kubernetes/pkg/kubelet/eviction"
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"k8s.io/kubernetes/pkg/kubelet/lifecycle"
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"k8s.io/kubernetes/pkg/kubelet/metrics"
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kubetypes "k8s.io/kubernetes/pkg/kubelet/types"
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"k8s.io/kubernetes/pkg/kubelet/util/format"
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)
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const message = "Preempted in order to admit critical pod"
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// CriticalPodAdmissionHandler is an AdmissionFailureHandler that handles admission failure for Critical Pods.
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// If the ONLY admission failures are due to insufficient resources, then CriticalPodAdmissionHandler evicts pods
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// so that the critical pod can be admitted. For evictions, the CriticalPodAdmissionHandler evicts a set of pods that
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// frees up the required resource requests. The set of pods is designed to minimize impact, and is prioritized according to the ordering:
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// minimal impact for guaranteed pods > minimal impact for burstable pods > minimal impact for besteffort pods.
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// minimal impact is defined as follows: fewest pods evicted > fewest total requests of pods.
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// finding the fewest total requests of pods is considered besteffort.
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type CriticalPodAdmissionHandler struct {
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getPodsFunc eviction.ActivePodsFunc
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killPodFunc eviction.KillPodFunc
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recorder record.EventRecorder
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}
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var _ lifecycle.AdmissionFailureHandler = &CriticalPodAdmissionHandler{}
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func NewCriticalPodAdmissionHandler(getPodsFunc eviction.ActivePodsFunc, killPodFunc eviction.KillPodFunc, recorder record.EventRecorder) *CriticalPodAdmissionHandler {
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return &CriticalPodAdmissionHandler{
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getPodsFunc: getPodsFunc,
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killPodFunc: killPodFunc,
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recorder: recorder,
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}
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}
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// HandleAdmissionFailure gracefully handles admission rejection, and, in some cases,
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// to allow admission of the pod despite its previous failure.
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func (c *CriticalPodAdmissionHandler) HandleAdmissionFailure(admitPod *v1.Pod, failureReasons []lifecycle.PredicateFailureReason) ([]lifecycle.PredicateFailureReason, error) {
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if !kubetypes.IsCriticalPod(admitPod) {
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return failureReasons, nil
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}
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// InsufficientResourceError is not a reason to reject a critical pod.
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// Instead of rejecting, we free up resources to admit it, if no other reasons for rejection exist.
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nonResourceReasons := []lifecycle.PredicateFailureReason{}
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resourceReasons := []*admissionRequirement{}
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for _, reason := range failureReasons {
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if r, ok := reason.(*lifecycle.InsufficientResourceError); ok {
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resourceReasons = append(resourceReasons, &admissionRequirement{
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resourceName: r.ResourceName,
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quantity: r.GetInsufficientAmount(),
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})
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} else {
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nonResourceReasons = append(nonResourceReasons, reason)
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}
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}
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if len(nonResourceReasons) > 0 {
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// Return only reasons that are not resource related, since critical pods cannot fail admission for resource reasons.
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return nonResourceReasons, nil
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}
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err := c.evictPodsToFreeRequests(admitPod, admissionRequirementList(resourceReasons))
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// if no error is returned, preemption succeeded and the pod is safe to admit.
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return nil, err
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}
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// evictPodsToFreeRequests takes a list of insufficient resources, and attempts to free them by evicting pods
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// based on requests. For example, if the only insufficient resource is 200Mb of memory, this function could
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// evict a pod with request=250Mb.
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func (c *CriticalPodAdmissionHandler) evictPodsToFreeRequests(admitPod *v1.Pod, insufficientResources admissionRequirementList) error {
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podsToPreempt, err := getPodsToPreempt(admitPod, c.getPodsFunc(), insufficientResources)
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if err != nil {
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return fmt.Errorf("preemption: error finding a set of pods to preempt: %v", err)
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}
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klog.Infof("preemption: attempting to evict pods %v, in order to free up resources: %s", podsToPreempt, insufficientResources.toString())
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for _, pod := range podsToPreempt {
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status := v1.PodStatus{
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Phase: v1.PodFailed,
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Message: message,
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Reason: events.PreemptContainer,
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}
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// record that we are evicting the pod
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c.recorder.Eventf(pod, v1.EventTypeWarning, events.PreemptContainer, message)
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// this is a blocking call and should only return when the pod and its containers are killed.
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err := c.killPodFunc(pod, status, nil)
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if err != nil {
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klog.Warningf("preemption: pod %s failed to evict %v", format.Pod(pod), err)
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// In future syncPod loops, the kubelet will retry the pod deletion steps that it was stuck on.
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continue
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}
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if len(insufficientResources) > 0 {
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metrics.Preemptions.WithLabelValues(insufficientResources[0].resourceName.String()).Inc()
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} else {
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metrics.Preemptions.WithLabelValues("").Inc()
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}
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klog.Infof("preemption: pod %s evicted successfully", format.Pod(pod))
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}
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return nil
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}
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// getPodsToPreempt returns a list of pods that could be preempted to free requests >= requirements
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func getPodsToPreempt(pod *v1.Pod, pods []*v1.Pod, requirements admissionRequirementList) ([]*v1.Pod, error) {
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bestEffortPods, burstablePods, guaranteedPods := sortPodsByQOS(pod, pods)
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// make sure that pods exist to reclaim the requirements
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unableToMeetRequirements := requirements.subtract(append(append(bestEffortPods, burstablePods...), guaranteedPods...)...)
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if len(unableToMeetRequirements) > 0 {
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return nil, fmt.Errorf("no set of running pods found to reclaim resources: %v", unableToMeetRequirements.toString())
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}
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// find the guaranteed pods we would need to evict if we already evicted ALL burstable and besteffort pods.
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guaranteedToEvict, err := getPodsToPreemptByDistance(guaranteedPods, requirements.subtract(append(bestEffortPods, burstablePods...)...))
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if err != nil {
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return nil, err
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}
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// Find the burstable pods we would need to evict if we already evicted ALL besteffort pods, and the required guaranteed pods.
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burstableToEvict, err := getPodsToPreemptByDistance(burstablePods, requirements.subtract(append(bestEffortPods, guaranteedToEvict...)...))
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if err != nil {
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return nil, err
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}
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// Find the besteffort pods we would need to evict if we already evicted the required guaranteed and burstable pods.
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bestEffortToEvict, err := getPodsToPreemptByDistance(bestEffortPods, requirements.subtract(append(burstableToEvict, guaranteedToEvict...)...))
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if err != nil {
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return nil, err
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}
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return append(append(bestEffortToEvict, burstableToEvict...), guaranteedToEvict...), nil
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}
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// getPodsToPreemptByDistance finds the pods that have pod requests >= admission requirements.
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// Chooses pods that minimize "distance" to the requirements.
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// If more than one pod exists that fulfills the remaining requirements,
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// it chooses the pod that has the "smaller resource request"
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// This method, by repeatedly choosing the pod that fulfills as much of the requirements as possible,
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// attempts to minimize the number of pods returned.
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func getPodsToPreemptByDistance(pods []*v1.Pod, requirements admissionRequirementList) ([]*v1.Pod, error) {
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podsToEvict := []*v1.Pod{}
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// evict pods by shortest distance from remaining requirements, updating requirements every round.
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for len(requirements) > 0 {
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if len(pods) == 0 {
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return nil, fmt.Errorf("no set of running pods found to reclaim resources: %v", requirements.toString())
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}
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// all distances must be less than len(requirements), because the max distance for a single requirement is 1
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bestDistance := float64(len(requirements) + 1)
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bestPodIndex := 0
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// Find the pod with the smallest distance from requirements
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// Or, in the case of two equidistant pods, find the pod with "smaller" resource requests.
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for i, pod := range pods {
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dist := requirements.distance(pod)
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if dist < bestDistance || (bestDistance == dist && smallerResourceRequest(pod, pods[bestPodIndex])) {
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bestDistance = dist
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bestPodIndex = i
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}
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}
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// subtract the pod from requirements, and transfer the pod from input-pods to pods-to-evicted
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requirements = requirements.subtract(pods[bestPodIndex])
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podsToEvict = append(podsToEvict, pods[bestPodIndex])
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pods[bestPodIndex] = pods[len(pods)-1]
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pods = pods[:len(pods)-1]
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}
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return podsToEvict, nil
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}
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type admissionRequirement struct {
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resourceName v1.ResourceName
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quantity int64
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}
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type admissionRequirementList []*admissionRequirement
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// distance returns distance of the pods requests from the admissionRequirements.
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// The distance is measured by the fraction of the requirement satisfied by the pod,
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// so that each requirement is weighted equally, regardless of absolute magnitude.
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func (a admissionRequirementList) distance(pod *v1.Pod) float64 {
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dist := float64(0)
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for _, req := range a {
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remainingRequest := float64(req.quantity - resource.GetResourceRequest(pod, req.resourceName))
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if remainingRequest > 0 {
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dist += math.Pow(remainingRequest/float64(req.quantity), 2)
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}
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}
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return dist
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}
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// subtract returns a new admissionRequirementList containing remaining requirements if the provided pod
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// were to be preempted
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func (a admissionRequirementList) subtract(pods ...*v1.Pod) admissionRequirementList {
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newList := []*admissionRequirement{}
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for _, req := range a {
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newQuantity := req.quantity
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for _, pod := range pods {
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newQuantity -= resource.GetResourceRequest(pod, req.resourceName)
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if newQuantity <= 0 {
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break
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}
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}
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if newQuantity > 0 {
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newList = append(newList, &admissionRequirement{
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resourceName: req.resourceName,
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quantity: newQuantity,
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})
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}
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}
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return newList
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}
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func (a admissionRequirementList) toString() string {
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s := "["
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for _, req := range a {
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s += fmt.Sprintf("(res: %v, q: %d), ", req.resourceName, req.quantity)
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}
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return s + "]"
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}
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// sortPodsByQOS returns lists containing besteffort, burstable, and guaranteed pods that
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// can be preempted by preemptor pod.
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func sortPodsByQOS(preemptor *v1.Pod, pods []*v1.Pod) (bestEffort, burstable, guaranteed []*v1.Pod) {
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for _, pod := range pods {
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if kubetypes.Preemptable(preemptor, pod) {
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switch v1qos.GetPodQOS(pod) {
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case v1.PodQOSBestEffort:
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bestEffort = append(bestEffort, pod)
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case v1.PodQOSBurstable:
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burstable = append(burstable, pod)
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case v1.PodQOSGuaranteed:
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guaranteed = append(guaranteed, pod)
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default:
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}
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}
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}
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return
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}
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// smallerResourceRequest returns true if pod1 has a smaller request than pod2
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func smallerResourceRequest(pod1 *v1.Pod, pod2 *v1.Pod) bool {
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priorityList := []v1.ResourceName{
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v1.ResourceMemory,
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v1.ResourceCPU,
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}
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for _, res := range priorityList {
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req1 := resource.GetResourceRequest(pod1, res)
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req2 := resource.GetResourceRequest(pod2, res)
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if req1 < req2 {
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return true
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} else if req1 > req2 {
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return false
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}
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}
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return true
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}
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