背景：

根据当前pod的负载，动态调整 pod副本数量，业务高峰期自动扩容pod的副本数以尽快响应pod的请求。
在业务低峰期对pod进行缩容，实现降本增效的目的。

动态伸缩控制器类型：

水平pod自动缩放器(HPA)：基于pod 资源利用率横向调整pod副本数量。
垂直pod自动缩放器(VPA)：基于pod资源利用率，调整对单个pod的最大资源限制，不能与HPA同时使用。
集群伸缩(Cluster Autoscaler,CA)：基于集群中node 资源使用情况，动态伸缩node节点，从而保证有CPU和内存资源用于创建pod。

具体执行过程参照下图：

HPA控制器简介：

Horizontal Pod Autoscaling (HPA)控制器，根据预定义好的阈值及pod当前的资源利用率，自动控制在k8s集群中运行的pod数量(自动弹性水平自动伸缩).
指标说明：
horizontal-pod-autoscaler-sync-period #默认每隔15s(可以通过–horizontal-pod-autoscaler-sync-period修改)查询metrics的资源使用情况。
horizontal-pod-autoscaler-downscale-stabilization #缩容间隔周期，默认5分钟。
horizontal-pod-autoscaler-sync-period #HPA控制器同步pod副本数的间隔周期
horizontal-pod-autoscaler-cpu-initialization-period #初始化延迟时间，在此时间内 pod的CPU 资源指标将不会生效，默认为5分钟。
horizontal-pod-autoscaler-initial-readiness-delay #用于设置 pod 准备时间，在此时间内的 pod 统统被认为未就绪及不采集数据,默认为30秒。

kube-controller-manager --help|grep horizontal-pod-autoscaler-downscale-stabilization #可以查看具体的默认值
注意：
horizontal-pod-autoscaler-tolerance #HPA控制器能容忍的数据差异(浮点数，默认为0.1)，即新的指标要与当前的阈值差异在0.1或以上,即要大于1+0.1=1.1，或小于1-0.1=0.9，比如阈值为CPU利用率50%,当前为80%,那么80/50=1.6 > 1.1则会触发扩容，反之会缩容。即触发条件：avg(CurrentPodsConsumption) / Target >1.1 或 <0.9=把N个pod的数据相加后根据pod的数量计算出平均数除以阈值,大于1.1就扩容，小于0.9就缩容。

计算公式：TargetNumOfPods = ceil(sum(CurrentPodsCPUUtilization) / Target) #ceil是一个向上取整的目的pod整数。

指标数据需要部署metrics-server，即HPA使用metrics-server作为数据源。

部署metric-server

资源文件下载地址：
https://github.com/kubernetes-sigs/metrics-server
kubectl apply -f metrics-server.yaml #部署metric-server
kubectl top pod xxx -n ns #查看pod指标
kubectl top node xxx #查看node指标

实战案例【基于k8s1.24.2版本】：

tomcat.yaml

apiVersion: apps/v1
kind: Deployment
metadata:name: mytomcat
spec:replicas: 5selector:matchLabels:app: mytomcatminReadySeconds: 1progressDeadlineSeconds: 60revisionHistoryLimit: 5strategy:type: RollingUpdaterollingUpdate:maxSurge: 1maxUnavailable: 1template:metadata:name: mytomcatlabels:app: mytomcatspec:containers:- name: mytomcatimage: tomcat:8ports:- containerPort: 8080
---
apiVersion: v1
kind: Service
metadata:name: mytomcat
spec:#type: NodePortports:- port: 8080#nodePort: 30090selector:app: mytomcat

hap.yaml

apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
metadata:namespace: demoname: demo-tomcat-podautoscalerlabels:app: demo-tomcat
spec:scaleTargetRef:apiVersion: apps/v1kind: Deploymentname: mytomcat                       minReplicas: 2maxReplicas: 8targetCPUUtilizationPercentage: 60

root@ubuntu01:/app# kubectl get pod -n demo
NAME                                         READY   STATUS    RESTARTS      AGE
myserver-nginx-deployment-56f4ccb9bd-9kjlc   1/1     Running   7 (47m ago)   14d
mytomcat-689d96db6f-4t9lh                    1/1     Running   0             8m29s
mytomcat-689d96db6f-c29sl                    1/1     Running   0             8m30s
mytomcat-689d96db6f-dhhmm                    1/1     Running   0             6s
mytomcat-689d96db6f-vsmph                    1/1     Running   0             7m35s
mytomcat-689d96db6f-w6fwq                    1/1     Running   0             7m35sroot@ubuntu01:/app# kubectl describe hpa demo-tomcat-podautoscaler  -n demo
Warning: autoscaling/v2beta2 HorizontalPodAutoscaler is deprecated in v1.23+, unavailable in v1.26+; use autoscaling/v2 HorizontalPodAutoscaler
Name:                                                  demo-tomcat-podautoscaler
Namespace:                                             demo
Labels:                                                app=demo-tomcat
Annotations:                                           <none>
CreationTimestamp:                                     Fri, 19 Aug 2022 21:32:01 +0800
Reference:                                             Deployment/mytomcat
Metrics:                                               ( current / target )resource cpu on pods  (as a percentage of request):  2% (2m) / 60%
Min replicas:                                          2
Max replicas:                                          8
Deployment pods:                                       2 current / 2 desired
Conditions:Type            Status  Reason               Message----            ------  ------               -------AbleToScale     True    ScaleDownStabilized  recent recommendations were higher than current one, applying the highest recent recommendationScalingActive   True    ValidMetricFound     the HPA was able to successfully calculate a replica count from cpu resource utilization (percentage of request)ScalingLimited  False   DesiredWithinRange   the desired count is within the acceptable range
Events:Type    Reason             Age    From                       Message----    ------             ----   ----                       -------Normal  SuccessfulRescale  3m40s  horizontal-pod-autoscaler  New size: 4; reason: All metrics below targetNormal  SuccessfulRescale  54s    horizontal-pod-autoscaler  New size: 2; reason: All metrics below target

从上面可以看出由最初的5个pod副本数降为hpa控制器最小的2个

将上面deployment资源文件镜像修改为：
image: lorel/docker-stress-ng
args: [“–vm”,“2”,“–vm-bytes”,“256M”]

apiVersion: apps/v1
kind: Deployment
metadata:name: mytomcat
spec:replicas: 2selector:matchLabels:app: mytomcatminReadySeconds: 1progressDeadlineSeconds: 60revisionHistoryLimit: 5strategy:type: RollingUpdaterollingUpdate:maxSurge: 1maxUnavailable: 1template:metadata:name: mytomcatlabels:app: mytomcatspec:containers:- name: mytomcatimage: lorel/docker-stress-ngargs: ["--vm","2","--vm-bytes","256M"]ports:- containerPort: 8080resources:requests:cpu: 100mmemory: 100Milimits:cpu: 100mmemory: 100Miroot@ubuntu01:/app# kubectl describe hpa demo-tomcat-podautoscaler -n demo
Warning: autoscaling/v2beta2 HorizontalPodAutoscaler is deprecated in v1.23+, unavailable in v1.26+; use autoscaling/v2 HorizontalPodAutoscaler
Name:                                                  demo-tomcat-podautoscaler
Namespace:                                             demo
Labels:                                                app=demo-tomcat
Annotations:                                           <none>
CreationTimestamp:                                     Fri, 19 Aug 2022 21:50:01 +0800
Reference:                                             Deployment/mytomcat
Metrics:                                               ( current / target )resource cpu on pods  (as a percentage of request):  87% (87m) / 60%
Min replicas:                                          2
Max replicas:                                          8
Deployment pods:                                       7 current / 8 desired
Conditions:Type            Status  Reason            Message----            ------  ------            -------AbleToScale     True    SucceededRescale  the HPA controller was able to update the target scale to 8ScalingActive   True    ValidMetricFound  the HPA was able to successfully calculate a replica count from cpu resource utilization (percentage of request)ScalingLimited  True    TooManyReplicas   the desired replica count is more than the maximum replica count
Events:Type     Reason                        Age                   From                       Message----     ------                        ----                  ----                       -------Normal   SuccessfulRescale             32m                   horizontal-pod-autoscaler  New size: 4; reason: All metrics below targetNormal   SuccessfulRescale             30m                   horizontal-pod-autoscaler  New size: 2; reason: All metrics below targetWarning  FailedGetScale                4m39s                 horizontal-pod-autoscaler  deployments/scale.apps "mytomcat" not foundWarning  FailedGetResourceMetric       4m9s (x2 over 4m24s)  horizontal-pod-autoscaler  failed to get cpu utilization: unable to get metrics for resource cpu: no metrics returned from resource metrics APIWarning  FailedComputeMetricsReplicas  4m9s (x2 over 4m24s)  horizontal-pod-autoscaler  invalid metrics (1 invalid out of 1), first error is: failed to get cpu utilization: unable to get metrics for resource cpu: no metrics returned from resource metrics APIWarning  FailedGetResourceMetric       3m54s                 horizontal-pod-autoscaler  failed to get cpu utilization: did not receive metrics for any ready podsWarning  FailedComputeMetricsReplicas  3m54s                 horizontal-pod-autoscaler  invalid metrics (1 invalid out of 1), first error is: failed to get cpu utilization: did not receive metrics for any ready podsNormal   SuccessfulRescale             2m54s                 horizontal-pod-autoscaler  New size: 4; reason: cpu resource utilization (percentage of request) above targetNormal   SuccessfulRescale             98s                   horizontal-pod-autoscaler  New size: 5; reason: cpu resource utilization (percentage of request) above targetNormal   SuccessfulRescale             83s                   horizontal-pod-autoscaler  New size: 7; reason: cpu resource utilization (percentage of request) above targetNormal   SuccessfulRescale             20s                   horizontal-pod-autoscaler  New size: 8; reason: cpu resource utilization (percentage of request) above targetroot@ubuntu01:/app# kubectl get pod -n demo
NAME                                         READY   STATUS    RESTARTS      AGE
myserver-nginx-deployment-56f4ccb9bd-9kjlc   1/1     Running   7 (83m ago)   14d
mytomcat-76798bc994-2gxxf                    1/1     Running   0             5m51s
mytomcat-76798bc994-2z5cm                    1/1     Running   0             4m35s
mytomcat-76798bc994-5s2tf                    1/1     Running   0             4m20s
mytomcat-76798bc994-dlbgf                    1/1     Running   0             4m20s
mytomcat-76798bc994-dncl4                    1/1     Running   0             5m51s
mytomcat-76798bc994-f5b5c                    1/1     Running   0             7m36s
mytomcat-76798bc994-r59j7                    1/1     Running   0             3m17s
mytomcat-76798bc994-rzl5w                    1/1     Running   0             7m36s

从图中可以看出扩容到8个副本数后即使还是超过阀值，但由于hpa控制器最大pod副本数为8，故到8个后pod副本数不在进行扩容。

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HPA控制器介绍以及实战案例

背景：

动态伸缩控制器类型：

HPA控制器简介：

部署metric-server

实战案例【基于k8s1.24.2版本】：

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