Horizontal Pod Autoscaling（Pod水平自动伸缩），简称HPA。HAP通过监控分析RC或者Deployment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，这是HPA最基本的原理。
HPA在kubernetes集群中被设计成一个controller，HPA Controller默认30s轮询一次（可通过kube-controller-manager的标志--horizontal-pod-autoscaler-sync-period进行设置），查询指定的资源（RC或者Deployment）中Pod的资源使用率，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。
HPA可以从两个地方获取数据：
1、Heapster：仅支持CPU使用率
2、自定义监控

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安装配置heapster
https://github.com/kubernetes-retired/heapster/tree/v1.4.2/deploy/kube-config/influxdb
$ docker pull docker.io/zhaoqing/heapster-amd64:1.4.2
$ docker pull docker.io/pupudaye/heapster-influxdb-amd64:v1.3.3
1、安装heapster数据库influxdb

---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: monitoring-influxdb
  namespace: kube-system
spec:
  replicas: 1
  template:
    metadata:
      labels:
        task: monitoring
        k8s-app: influxdb
    spec:
      containers:
      - name: influxdb
        image: docker.io/pupudaye/heapster-influxdb-amd64:v1.3.3
        volumeMounts:
        - mountPath: /data
          name: influxdb-storage
      volumes:
      - name: influxdb-storage
        emptyDir: {}
---
apiVersion: v1
kind: Service
metadata:
  labels:
    task: monitoring
    kubernetes.io/cluster-service: 'true'
    kubernetes.io/name: monitoring-influxdb
  name: monitoring-influxdb
  namespace: kube-system
spec:
  ports:
  - port: 8086
    targetPort: 8086
  selector:
    k8s-app: influxdb

2、安装heapster

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: heapster
  namespace: kube-system
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: dongyali-sa2-clusterrolebinding
subjects:
- kind: ServiceAccount
  name: heapster
  namespace: kube-system
roleRef:
  kind: ClusterRole
  name: cluster-admin
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: heapster
  namespace: kube-system
spec:
  replicas: 1
  template:
    metadata:
      labels:
        task: monitoring
        k8s-app: heapster
    spec:
      serviceAccountName: heapster
      containers:
      - name: heapster
        image: docker.io/zhaoqing/heapster-amd64:1.4.2
        imagePullPolicy: IfNotPresent
        command:
        - /heapster
        - --source=kubernetes:https://kubernetes.default
        - --sink=influxdb:http://monitoring-influxdb.kube-system.svc:8086
---
apiVersion: v1
kind: Service
metadata:
  labels:
    task: monitoring
    kubernetes.io/cluster-service: 'true'
    kubernetes.io/name: Heapster
  name: heapster
  namespace: kube-system
spec:
  ports:
  - port: 80
    targetPort: 8082
  selector:
    k8s-app: heapster

3、修改kube-controller-manager.yaml
$ cd /etc/kubernetes/manifests/
$ vim kube-controller-manager.yaml

spec:
  containers:
  - command:
    - kube-controller-manager
    - --horizontal-pod-autoscaler-use-rest-clients=false         #增加

修改后自动生效
4、创建应用pod用户测试hpa

apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: hpa-nginx-deploy
  labels:
    app: nginx-demo
spec:
  revisionHistoryLimit: 15
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        resources:
          requests:
            cpu: 100m
        ports:
        - containerPort: 80

5、针对上述pod创建hpa
$ kubectl autoscale deployment hpa-nginx-deploy --cpu-percent=10 --min=1 --max=10
设置最小的 pod 副本数为1，大为10。HPA会根据设定的 cpu使用率（10%）动态的增加或者减少pod数量。
$ kubectl get hpa
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS
hpa-nginx-deploy Deployment/hpa-nginx-deploy 0%/10% 1 10 1
$ kubectl get hpa hpa-nginx-deploy -o yaml
$ kubectl describe hpa hpa-nginx-deploy
6、用压力测试查看hpa变化情况
$ kubectl get pod -o wide|grep hpa
hpa-nginx-deploy-7db6976d9b-p7llf 1/1 Running 0 155m 10.244.2.250 server242.example.com
$ kubectl run -i --tty load-generator --image=busybox /bin/sh
/ # while true; do wget -q -O- http://10.244.2.250; done
在另一个终端查看
$ kubectl get hpa
$ kubectl get deployment hpa-nginx-deploy
$ kubectl delete deployments.apps load-generator

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