菜鸟学Kubernetes(K8s)系列——（番外）实现Deployment的动态扩缩容能力（HPA）

我们知道通过Deployment可以对Pod副本数进行动态扩缩容，但是这毕竟还是需要人为检测我们部署的服务的压力状况，然后去手动调整Pod的副本数量。**在Kubernetes中，有一种感知能力，可以在请求高峰期的时候动态扩容Pod的数量，在高峰期过去后动态缩容。**完全不需要人为干预。

想要实现动态扩缩容需要先准备一个Metrics服务器，这个服务器可以监控当前系统的指标。

安装Metrics

• 首先部署下面的资源（下面文件做了一些特殊修改，比如修改镜像地址等，可以直接使用）

  apiVersion: v1
  kind: ServiceAccount
  metadata:
    labels:
      k8s-app: metrics-server
    name: metrics-server
    namespace: kube-system
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: ClusterRole
  metadata:
    labels:
      k8s-app: metrics-server
      rbac.authorization.k8s.io/aggregate-to-admin: "true"
      rbac.authorization.k8s.io/aggregate-to-edit: "true"
      rbac.authorization.k8s.io/aggregate-to-view: "true"
    name: system:aggregated-metrics-reader
  rules:
  - apiGroups:
    - metrics.k8s.io
    resources:
    - pods
    - nodes
    verbs:
    - get
    - list
    - watch
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: ClusterRole
  metadata:
    labels:
      k8s-app: metrics-server
    name: system:metrics-server
  rules:
  - apiGroups:
    - ""
    resources:
    - nodes/metrics
    verbs:
    - get
  - apiGroups:
    - ""
    resources:
    - pods
    - nodes
    verbs:
    - get
    - list
    - watch
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: RoleBinding
  metadata:
    labels:
      k8s-app: metrics-server
    name: metrics-server-auth-reader
    namespace: kube-system
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: Role
    name: extension-apiserver-authentication-reader
  subjects:
  - kind: ServiceAccount
    name: metrics-server
    namespace: kube-system
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: ClusterRoleBinding
  metadata:
    labels:
      k8s-app: metrics-server
    name: metrics-server:system:auth-delegator
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: ClusterRole
    name: system:auth-delegator
  subjects:
  - kind: ServiceAccount
    name: metrics-server
    namespace: kube-system
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: ClusterRoleBinding
  metadata:
    labels:
      k8s-app: metrics-server
    name: system:metrics-server
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: ClusterRole
    name: system:metrics-server
  subjects:
  - kind: ServiceAccount
    name: metrics-server
    namespace: kube-system
  ---
  apiVersion: v1
  kind: Service
  metadata:
    labels:
      k8s-app: metrics-server
    name: metrics-server
    namespace: kube-system
  spec:
    ports:
    - name: https
      port: 443
      protocol: TCP
      targetPort: https
    selector:
      k8s-app: metrics-server
  ---
  apiVersion: apps/v1
  kind: Deployment
  metadata:
    labels:
      k8s-app: metrics-server
    name: metrics-server
    namespace: kube-system
  spec:
    selector:
      matchLabels:
        k8s-app: metrics-server
    strategy:
      rollingUpdate:
        maxUnavailable: 0
    template:
      metadata:
        labels:
          k8s-app: metrics-server
      spec:
        nodeName: k8s-node1   ### 新增，为master节点的hostname
        containers:
        - args:
          - --cert-dir=/tmp
          - --secure-port=4430   ### 由原来的4443改为4430
          - --kubelet-preferred-address-types=InternalDNS,InternalIP,ExternalDNS,ExternalIP,Hostname ### 进行了修改，添加InternalDNS、ExternalDNS
          - --kubelet-use-node-status-port
          - --metric-resolution=15s
          - --kubelet-insecure-tls  ### 新增
          image: bitnami/metrics-server:0.6.1
          imagePullPolicy: IfNotPresent
          livenessProbe:
            failureThreshold: 3
            httpGet:
              path: /livez
              port: https
              scheme: HTTPS
            periodSeconds: 10
          name: metrics-server
          ports:
          - containerPort: 4430        ### 由原来的4443改为4430
            name: https
            protocol: TCP
          readinessProbe:
            failureThreshold: 3
            httpGet:
              path: /readyz
              port: https
              scheme: HTTPS
            initialDelaySeconds: 20
            periodSeconds: 10
          resources:
            requests:
              cpu: 100m
              memory: 200Mi
          securityContext:
            allowPrivilegeEscalation: false
            readOnlyRootFilesystem: true
            runAsNonRoot: true
            runAsUser: 1000
          volumeMounts:
          - mountPath: /tmp
            name: tmp-dir
        nodeSelector:
          kubernetes.io/os: linux
        priorityClassName: system-cluster-critical
        serviceAccountName: metrics-server
        volumes:
        - emptyDir: {}
          name: tmp-dir
  ---
  apiVersion: apiregistration.k8s.io/v1
  kind: APIService
  metadata:
    labels:
      k8s-app: metrics-server
    name: v1beta1.metrics.k8s.io
  spec:
    group: metrics.k8s.io
    groupPriorityMinimum: 100
    insecureSkipTLSVerify: true
    service:
      name: metrics-server
      namespace: kube-system
    version: v1beta1
    versionPriority: 100
  
  

• kubectl apply -f metrics.yaml 即可

• 测试：kubectl top node

  • 这里可能会报错

  Error from server (ServiceUnavailable): the server is currently unable to handle the request (get nodes.metrics.k8s.io)
  

  • 解决

    • 在/etc/kubernetes/manifests 里面改一下apiserver的配置

      • vim /etc/kubernetes/manifests/kube-apiserver.yaml

      • 在command下新增 - --enable-aggregator-routing=true
        

      • kubectl apply -f /etc/kubernetes/manifests/kube-apiserver.yaml

      • kubectl delete pods kube-apiserver -n kube-system

      • kubectl apply -f metrics.yaml

动态扩缩容的原理

首先Deployment会控制一个RS，RS控制各个Pod。Kubernetes通过HPA资源来实现实现对目标资源的监控，然后自动扩缩容。