本篇内容主要讲解“Kubernetes Resource QoS机制是什么”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Kubernetes Resource QoS机制是什么”吧!
Kubernetes Resource QoS Classes介绍
Kubernetes根据Pod中Containers Resource的request和limit的值来定义Pod的QoS Class。
对于每一种Resource都可以将容器分为3中QoS Classes: Guaranteed, Burstable, and Best-Effort，它们的QoS级别依次递减。
注意，如果一个容器只指明了limit，而未指明request，则表明request的值等于limit的值。
Examples:
containers:
name: foo
resources:
limits:
cpu: 10m
memory: 1Gi
name: bar
resources:
limits:
cpu: 100m
memory: 100Mi
containers:
name: foo
resources:
limits:
cpu: 10m
memory: 1Gi
requests:
cpu: 10m
memory: 1Gi
name: bar
resources:
limits:
cpu: 100m
memory: 100Mi
requests:
cpu: 100m
memory: 100Mi
Examples:
containers:
name: foo
resources:
name: bar
resources:
当limit值未指定时，其有效值其实是对应Node Resource的Capacity。
Examples:
容器bar没有对Resource进行指定。
containers:
name: foo
resources:
limits:
cpu: 10m
memory: 1Gi
requests:
cpu: 10m
memory: 1Gi
name: bar
容器foo和bar对不同的Resource进行了指定。
containers:
name: foo
resources:
limits:
memory: 1Gi
name: bar
resources:
limits:
cpu: 100m
容器foo未指定limit，容器bar未指定request和limit。
containers:
name: foo
resources:
requests:
cpu: 10m
memory: 1Gi
name: bar
可压缩/不可压缩资源的区别
kube-scheduler调度时，是基于Pod的request值进行Node Select完成调度的。Pod和它的所有Container都不允许Consume limit指定的有效值(if have)。
How the request and limit are enforced depends on whether the resource is compressible or incompressible.
Compressible Resource Guarantees
For now, we are only supporting CPU.
Pods are guaranteed to get the amount of CPU they request, they may or may not get additional CPU time (depending on the other jobs running). This isn't fully guaranteed today because cpu isolation is at the container level. Pod level cgroups will be introduced soon to achieve this goal.
Excess CPU resources will be distributed based on the amount of CPU requested. For example, suppose container A requests for 600 milli CPUs, and container B requests for 300 milli CPUs. Suppose that both containers are trying to use as much CPU as they can. Then the extra 10 milli CPUs will be distributed to A and B in a 2:1 ratio (implementation discussed in later sections).
Pods will be throttled if they exceed their limit. If limit is unspecified, then the pods can use excess CPU when available.
Incompressible Resource Guarantees
For now, we are only supporting memory.
Pods will get the amount of memory they request, if they exceed their memory request, they could be killed (if some other pod needs memory), but if pods consume less memory than requested, they will not be killed (except in cases where system tasks or daemons need more memory).
When Pods use more memory than their limit, a process that is using the most amount of memory, inside one of the pod's containers, will be killed by the kernel.
Admission/Scheduling Policy
如何根据不同的QoS回收Resources
CPU Pods will not be killed if CPU guarantees cannot be met (for example if system tasks or daemons take up lots of CPU), they will be temporarily throttled.
Memory Memory is an incompressible resource and so let's discuss the semantics of memory management a bit.
Best-Effort pods will be treated as lowest priority. Processes in these pods are the first to get killed if the system runs out of memory. These containers can use any amount of free memory in the node though.
Guaranteed pods are considered top-priority and are guaranteed to not be killed until they exceed their limits, or if the system is under memory pressure and there are no lower priority containers that can be evicted.
Burstable pods have some form of minimal resource guarantee, but can use more resources when available. Under system memory pressure, these containers are more likely to be killed once they exceed their requests and no Best-Effort pods exist.
OOM Score configuration at the Nodes
Pod OOM score configuration
Note that the OOM score of a process is 10 times the % of memory the process consumes, adjusted by OOM_SCORE_ADJ, barring exceptions (e.g. process is launched by root). Processes with higher OOM scores are killed.
The base OOM score is between 0 and 1000, so if process A’s OOM_SCORE_ADJ - process B’s OOM_SCORE_ADJ is over a 1000, then process A will always be OOM killed before B.
The final OOM score of a process is also between 0 and 1000
Best-effort
Guaranteed
Burstable
If total memory request > 99.8% of available memory, OOM_SCORE_ADJ: 2
Otherwise, set OOM_SCORE_ADJ to 1000 - 10 * (% of memory requested)
This ensures that the OOM_SCORE of burstable pod is > 1
If memory request is 0, OOM_SCORE_ADJ is set to 999.
So burstable pods will be killed if they conflict with guaranteed pods
If a burstable pod uses less memory than requested, its OOM_SCORE < 1000
So best-effort pods will be killed if they conflict with burstable pods using less than requested memory
If a process in burstable pod's container uses more memory than what the container had requested, its OOM_SCORE will be 1000, if not its OOM_SCORE will be < 1000
Assuming that a container typically has a single big process, if a burstable pod's container that uses more memory than requested conflicts with another burstable pod's container using less memory than requested, the former will be killed
If burstable pod's containers with multiple processes conflict, then the formula for OOM scores is a heuristic, it will not ensure "Request and Limit" guarantees.
Pod infra containers or Special Pod init process
Kubelet, Docker
OOM_SCORE_ADJ: -999 (won’t be OOM killed)
Hack, because these critical tasks might die if they conflict with guaranteed containers. In the future, we should place all user-pods into a separate cgroup, and set a limit on the memory they can consume.
源码分析
QoS的源码位于：pkg/kubelet/qos，代码非常简单，主要就两个文件pkg/kubelet/qos/policy.go,pkg/kubelet/qos/qos.go。
上面讨论的各个QoS Class对应的OOM_SCORE_ADJ定义在：
pkg/kubelet/qos/policy.go:21
const (
PodInfraOOMAdj int = -998
KubeletOOMScoreAdj int = -999
DockerOOMScoreAdj int = -999
KubeProxyOOMScoreAdj int = -999
guaranteedOOMScoreAdj int = -998
besteffortOOMScoreAdj int = 1000
)
容器的OOM_SCORE_ADJ的计算方法定义在：
pkg/kubelet/qos/policy.go:40
func GetContainerOOMScoreAdjust(pod *v1.Pod, container *v1.Container, memoryCapacity int64) int {
switch GetPodQOS(pod) {
case Guaranteed:
// Guaranteed containers should be the last to get killed.
return guaranteedOOMScoreAdj
case BestEffort:
return besteffortOOMScoreAdj
}
// Burstable containers are a middle tier, between Guaranteed and Best-Effort. Ideally,
// we want to protect Burstable containers that consume less memory than requested.
// The formula below is a heuristic. A container requesting for 10% of a system's
// memory will have an OOM score adjust of 900. If a process in container Y
// uses over 10% of memory, its OOM score will be 1000. The idea is that containers
// which use more than their request will have an OOM score of 1000 and will be prime
// targets for OOM kills.
// Note that this is a heuristic, it won't work if a container has many small processes.
memoryRequest := container.Resources.Requests.Memory().Value()
oomScoreAdjust := 1000 - (1000*memoryRequest)/memoryCapacity
// A guaranteed pod using 100% of memory can have an OOM score of 10. Ensure
// that burstable pods have a higher OOM score adjustment.
if int(oomScoreAdjust) < (1000 + guaranteedOOMScoreAdj) {
return (1000 + guaranteedOOMScoreAdj)
}
// Give burstable pods a higher chance of survival over besteffort pods.
if int(oomScoreAdjust) == besteffortOOMScoreAdj {
return int(oomScoreAdjust - 1)
}
return int(oomScoreAdjust)
}获取Pod的QoS Class的方法为：
pkg/kubelet/qos/qos.go:50
// GetPodQOS returns the QoS class of a pod.
// A pod is besteffort if none of its containers have specified any requests or limits.
// A pod is guaranteed only when requests and limits are specified for all the containers and they are equal.
// A pod is burstable if limits and requests do not match across all containers.
func GetPodQOS(pod *v1.Pod) QOSClass {
requests := v1.ResourceList{}
limits := v1.ResourceList{}
zeroQuantity := resource.MustParse("0")
isGuaranteed := true
for _, container := range pod.Spec.Containers {
// process requests
for name, quantity := range container.Resources.Requests {
if !supportedQoSComputeResources.Has(string(name)) {
continue
}
if quantity.Cmp(zeroQuantity) == 1 {
delta := quantity.Copy()
if _, exists := requests[name]; !exists {
requests[name] = *delta
} else {
delta.Add(requests[name])
requests[name] = *delta
}
}
}
// process limits
qosLimitsFound := sets.NewString()
for name, quantity := range container.Resources.Limits {
if !supportedQoSComputeResources.Has(string(name)) {
continue
}
if quantity.Cmp(zeroQuantity) == 1 {
qosLimitsFound.Insert(string(name))
delta := quantity.Copy()
if _, exists := limits[name]; !exists {
limits[name] = *delta
} else {
delta.Add(limits[name])
limits[name] = *delta
}
}
}
if len(qosLimitsFound) != len(supportedQoSComputeResources) {
isGuaranteed = false
}
}
if len(requests) == 0 && len(limits) == 0 {
return BestEffort
}
// Check is requests match limits for all resources.
if isGuaranteed {
for name, req := range requests {
if lim, exists := limits[name]; !exists || lim.Cmp(req) != 0 {
isGuaranteed = false
break
}
}
}
if isGuaranteed &&
len(requests) == len(limits) {
return Guaranteed
}
return Burstable
}PodQoS会在eviction_manager和scheduler的Predicates阶段被调用，也就说会在k8s处理超配和调度预选阶段中被使用。
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