降低负载后Kubernetes HPA不会缩小

问题描述

当Pod的负载增加时，Kubernetes HPA可以正常工作，但是在负载减少之后，部署规模不会改变。这是我的HPA文件：

apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
  name: baseinformationmanagement
  namespace: default
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: baseinformationmanagement
  minReplicas: 1
  maxReplicas: 3
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 80
  - type: Resource
    resource:
      name: memory
      target:
        type: Utilization
        averageUtilization: 80

我的kubernetes版本：

> kubectl version
Client Version: version.Info{Major:"1",Minor:"16",GitVersion:"v1.16.1",GitCommit:"d647ddbd755faf07169599a625faf302ffc34458",GitTreeState:"clean",BuildDate:"2019-10-02T17:01:15Z",GoVersion:"go1.12.10",Compiler:"gc",Platform:"linux/amd64"}
Server Version: version.Info{Major:"1",Minor:"17",GitVersion:"v1.17.2",GitCommit:"59603c6e503c87169aea6106f57b9f242f64df89",BuildDate:"2020-01-18T23:22:30Z",GoVersion:"go1.13.5",Platform:"linux/amd64"}

这是我对HPA的描述：

> kubectl describe hpa baseinformationmanagement
Name:                                                     baseinformationmanagement
Namespace:                                                default
Labels:                                                   <none>
Annotations:                                              kubectl.kubernetes.io/last-applied-configuration:
                                                            {"apiVersion":"autoscaling/v2beta2","kind":"HorizontalPodAutoscaler","metadata":{"annotations":{},"name":"baseinformationmanagement","name...
CreationTimestamp:                                        Sun,27 Sep 2020 06:09:07 +0000
Reference:                                                Deployment/baseinformationmanagement
Metrics:                                                  ( current / target )
  resource memory on pods  (as a percentage of request):  49% (1337899008) / 70%
  resource cpu on pods  (as a percentage of request):     2% (13m) / 50%
Min replicas:                                             1
Max replicas:                                             3
Deployment pods:                                          2 current / 2 desired
Conditions:
  Type            Status  Reason              Message
  ----            ------  ------              -------
  AbleToScale     True    ReadyForNewScale    recommended size matches current size
  ScalingActive   True    ValidMetricFound    the HPA was able to successfully calculate a replica count from memory resource utilization (percentage of request)
  ScalingLimited  False   DesiredWithinRange  the desired count is within the acceptable range
Events:           <none>

解决方法

您的HPA同时指定内存和CPU目标。 Horizontal Pod Autoscaler文档说明：

如果在Horizo​​ntalPodAutoscaler中指定了多个指标，则将对每个指标进行此计算，然后选择所需的最大副本数。

实际副本目标是当前副本计数以及当前和目标利用率（相同链接）的函数：

desiredReplicas = ceil[currentReplicas * ( currentMetricValue / desiredMetricValue )]

特别是对于内存：currentReplicas是2； currentMetricValue是49； desiredMetricValue是80。所以目标副本数是

desiredReplicas = ceil[       2        * (         49        /         80         )]
desiredReplicas = ceil[       2        *                   0.61                    ]
desiredReplicas = ceil[                          1.26                              ]
desiredReplicas = 2

即使您的服务完全空闲，这也将导致（至少）有2个副本，除非该服务选择将内存释放回操作系统；通常这取决于语言运行时，并且有点不受您的控制。

仅删除内存目标并仅基于CPU自动缩放可能会更好地满足您的期望。