Kubernetes HPA 在减少负载后不会缩小

Question

当pod的负载增加时，Kubernetes HPA可以正常工作，但在负载减少后，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", GitTreeState:"clean", BuildDate:"2020-01-18T23:22:30Z", GoVersion:"go1.13.5", Compiler:"gc", Platform:"linux/amd64"}

这是我的HPA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>

Answer 1

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

如果在HorizontalPodAutoscaler中指定了多个度量，则会对每个度量进行此计算，然后选择所需副本计数中最大的一个。

实际副本目标是当前副本计数以及当前和目标利用率(同一链接(的函数：

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

特别是对于内存：currentReplicas是2；CCD_ 2为49；CCD_ 3为80。所以目标副本计数是

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，这也会导致(至少(有2个副本，除非服务选择将内存释放回操作系统；这通常取决于语言运行时，并且有点超出您的控制范围。

只需移除内存目标并仅基于CPU进行自动缩放，就可以更好地满足您的期望。