HPA简介

在前面的学习中我们使用用一个 kubectl scale 命令可以来实现 Pod 的扩缩容功能，但是这个毕竟是完全手动操作的，要应对线上的各种复杂情况，我们需要能够做到自动化去感知业务，来自动进行扩缩容。为此，Kubernetes 也为我们提供了这样的一个资源对象：Horizontal Pod Autoscaling（Pod 水平自动伸缩），简称HPA，HPA 通过监控分析一些控制器控制的所有 Pod 的负载变化情况来确定是否需要调整 Pod 的副本数量

我们可以简单的通过 kubectl autoscale 命令来创建一个 HPA 资源对象，HPA Controller默认30s轮询一次（可通过 kube-controller-manager 的--horizontal-pod-autoscaler-sync-period 参数进行设置），查询指定的资源中的 Pod 资源使用率，并且与创建时设定的值和指标做对比，从而实现自动伸缩的功能。

在配置HPA前，需要先部署Metrics-Server，需要Metrics-Server提供 资源信息；

部署Pod

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[root@pool1 hpa-demo]# vi hpa-demo.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: hpa-demo
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: zx/nginx:latest
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
        resources:		# 想要Pod实现HPA自动扩缩容，前提必须配置resources资源请求；
          requests:
            memory: 50Mi
            cpu: 50m
          limits:
            memory: 100Mi
            cpu: 100m

部署Deployment

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[root@pool1 hpa-demo]# kubectl apply -f hpa-demo.yaml 
deployment.apps/hpa-demo created
[root@pool1 hpa-demo]# kubectl get pod -l app=nginx
NAME                        READY   STATUS        RESTARTS   AGE
hpa-demo-687f444c8c-sggmf   1/1     Running       0          5s
[root@pool1 hpa-demo]# kubectl autoscale deployment hpa-demo --cpu-percent=10 --min=1 --max=10 
horizontalpodautoscaler.autoscaling/hpa-demo autoscaled
[root@pool1 hpa-demo]# kubectl get hpa
NAME       REFERENCE             TARGETS         MINPODS   MAXPODS   REPLICAS   AGE
hpa-demo   Deployment/hpa-demo   <unknown>/10%   1         10        0          13s
[root@pool1 hpa-demo]# kubectl describe hpa hpa-demo
Name:                                                  hpa-demo
Namespace:                                             default
Labels:                                                <none>
Annotations:                                           <none>
CreationTimestamp:                                     Thu, 16 Dec 2021 16:50:42 +0800
Reference:                                             Deployment/hpa-demo
Metrics:                                               ( current / target )
  resource cpu on pods  (as a percentage of request):  0% (0) / 10%
Min replicas:                                          1
Max replicas:                                          10
Deployment pods:                                       1 current / 1 desired
Conditions:
  Type            Status  Reason               Message
  ----            ------  ------               -------
  AbleToScale     True    ScaleDownStabilized  recent recommendations were higher than current one, applying the highest recent recommendation
  ScalingActive   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:           <none>

可以看到HPA资源对象已经正常启用了

Pod压力测试

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[root@pool1 hpa-demo]# kubectl get pod -l app=nginx -o wide
NAME                        READY   STATUS    RESTARTS   AGE    IP              NODE    NOMINATED NODE   READINESS GATES
hpa-demo-687f444c8c-8b5p8   1/1     Running   0          89s    10.244.52.226   pool2   <none>           <none>
[root@pool1 hpa-demo]# kubectl run -it centos-test --image centos:7
[root@centos-test /]# while true;do curl -I 10.244.206.20;done
HTTP/1.1 200 OK
Server: nginx/1.11.1
Date: Thu, 16 Dec 2021 09:05:40 GMT
Content-Type: text/html
Content-Length: 612
Last-Modified: Fri, 22 May 2020 03:19:30 GMT
Connection: keep-alive
ETag: "5ec744c2-264"
Accept-Ranges: bytes
···
# 另开终端查看HPA效果
[root@pool1 ~]# kubectl get hpa
NAME       REFERENCE             TARGETS   MINPODS   MAXPODS   REPLICAS   AGE
hpa-demo   Deployment/hpa-demo   88%/10%   1         10        9          14m
[root@pool1 ~]# kubectl get pod -l app=nginx
NAME                        READY   STATUS    RESTARTS   AGE
hpa-demo-687f444c8c-8b5p8   1/1     Running   0          33s
hpa-demo-687f444c8c-9xmpp   1/1     Running   0          48s
hpa-demo-687f444c8c-fx525   1/1     Running   0          48s
hpa-demo-687f444c8c-hkhpm   1/1     Running   0          64s
hpa-demo-687f444c8c-lvh5z   1/1     Running   0          64s
hpa-demo-687f444c8c-mnbx2   1/1     Running   0          48s
hpa-demo-687f444c8c-sggmf   1/1     Running   0          18m
hpa-demo-687f444c8c-shbpq   1/1     Running   0          48s
hpa-demo-687f444c8c-z2kk7   1/1     Running   0          64s
[root@pool1 ~]# kubectl get pod -l app=nginx | wc -l
10

从一个Pod自动扩容到9个Pod，成功实现HPA自动扩容

等待5分钟自动缩放

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[root@pool1 ~]# kubectl get deployment hpa-demo
NAME       READY   UP-TO-DATE   AVAILABLE   AGE
hpa-demo   1/1     1            1           29m

成功从9个Pod缩放到1个Pod

缩放问题

从 Kubernetes v1.12 版本开始我们可以通过设置 kube-controller-manager 组件的--horizontal-pod-autoscaler-downscale-stabilization 参数来设置一个持续时间，用于指定在当前操作完成后，HPA 必须等待多长时间才能执行另一次缩放操作。默认为5分钟，也就是默认需要等待5分钟后才会开始自动缩放。