ACK 1.9 版本K8S更新指南

ACK 1.9已經超出技術支援期限，目前更新管控已經無法适配1.9更新，本文主要指導使用者修改1.9的相關配置，使其可以進行更新。

目前主要阻礙是1.9叢集内置的DNS服務元件為kube-dns，我們需要将其替換為CoreDNS，就可以使用容器服務提供的更新功能進行更新了。

首先，我們需要在叢集中部署CoreDNS服務。注意需要将image修改為您的叢集所在的regionid，如你的叢集在杭州則将

image: registry-vpc.YOUR-REGIONID.aliyuncs.com/acs/coredns:1.0.6           

修改為

image: registry-vpc.cn-hangzhou.aliyuncs.com/acs/coredns:1.0.6           

完整yaml檔案如下：

apiVersion: apps/v1
kind: Deployment
metadata:
  name: coredns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
spec:
  replicas: 2
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
  selector:
    matchLabels:
      k8s-app: kube-dns
  template:
    metadata:
      labels:
        k8s-app: kube-dns
    spec:
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 100
            podAffinityTerm:
              labelSelector:
                matchExpressions:
                  - key: k8s-app
                    operator: In
                    values: ["kube-dns"]
              topologyKey: kubernetes.io/hostname
      serviceAccountName: coredns
      tolerations:
      - operator: Exists
      nodeSelector:
        beta.kubernetes.io/os: linux
      containers:
      - name: coredns
        image: registry-vpc.YOUR-REGIONID.aliyuncs.com/acs/coredns:1.0.6
        imagePullPolicy: IfNotPresent
        resources:
          limits:
            memory: 170Mi
          requests:
            cpu: 100m
            memory: 70Mi
        args: [ "-conf", "/etc/coredns/Corefile" ]
        volumeMounts:
        - name: config-volume
          mountPath: /etc/coredns
          readOnly: true
        ports:
        - containerPort: 53
          name: dns
          protocol: UDP
        - containerPort: 53
          name: dns-tcp
          protocol: TCP
        - containerPort: 9153
          name: metrics
          protocol: TCP
        livenessProbe:
          httpGet:
            path: /health
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        securityContext:
          allowPrivilegeEscalation: false
          capabilities:
            add:
            - NET_BIND_SERVICE
            drop:
            - all
          readOnlyRootFilesystem: true
      dnsPolicy: Default
      volumes:
        - name: config-volume
          configMap:
            name: coredns
            items:
            - key: Corefile
              path: Corefile
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        health
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           upstream
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        proxy . /etc/resolv.conf
        cache 30
        loadbalance
    }
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: system:coredns
rules:
- apiGroups:
  - ""
  resources:
  - endpoints
  - services
  - pods
  - namespaces
  verbs:
  - list
  - watch
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: system:coredns
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: system:coredns
subjects:
- kind: ServiceAccount
  name: coredns
  namespace: kube-system
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: coredns
  namespace: kube-system           

使用該yaml建立CoreDNS服務後，需要觀察其是否可以正常運作。

确定CoreDNS正常運作之後，可以逐漸減少叢集中kube-dns的副本數（spec. replicas）。

最後在確定業務正常運作的前提下，我們可以删掉叢集中的kube-dns。

完成上述操作步驟之後，您就可以使用容器服務的叢集更新功能進行叢集更新了。

如果叢集更新之後又出現了kube-dns，您可以将其删除。