18.服务发现-CoreDNS

本节将通过向k8s内部署容器的方式来交付CoreDNS服务

一、获取CoreDNS

二进制包：https://github.com/coredns/coredns/releases
使用容器部署CoreDNS：https://registry.hub.docker.com/r/coredns/coredns/tags?page=1&ordering=last_updated
docker pull coredns/coredns:1.8.3

二、资源配置清单

参考：https://github.com/kubernetes/kubernetes/blob/v1.17.16/cluster/addons/dns/coredns/coredns.yaml.base

资源配置清单文件创建到node200:/data/k8s-yaml

1. RBAC

coredns_rbac.yaml

apiVersion: v1
kind: ServiceAccount
metadata:
  name: coredns
  namespace: kube-system
  labels:
      kubernetes.io/cluster-service: "true"
      addonmanager.kubernetes.io/mode: Reconcile
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  labels:
    kubernetes.io/bootstrapping: rbac-defaults
    addonmanager.kubernetes.io/mode: Reconcile
  name: system:coredns
rules:
- apiGroups:
  - ""
  resources:
  - endpoints
  - services
  - pods
  - namespaces
  verbs:
  - list
  - watch
- apiGroups:
  - ""
  resources:
  - nodes
  verbs:
  - get
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  annotations:
    rbac.authorization.kubernetes.io/autoupdate: "true"
  labels:
    kubernetes.io/bootstrapping: rbac-defaults
    addonmanager.kubernetes.io/mode: EnsureExists
  name: system:coredns
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: system:coredns
subjects:
- kind: ServiceAccount
  name: coredns
  namespace: kube-system

2. ConfigMap

coredns_configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
  labels:
      addonmanager.kubernetes.io/mode: EnsureExists
data:
  Corefile: |
    .:53 {
        errors
        health {
            lameduck 5s
        }
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {        # cluster.local 集群域名
            pods insecure
            fallthrough in-addr.arpa ip6.arpa
            ttl 30
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }

修改forward . 172.10.10.11可以将coredns的上级dns指定为我们之前搭建的bind9，这样容器内就能同步bind9的dns内容了

3. Deployment

coredns_dp.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: coredns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
    kubernetes.io/name: "CoreDNS"
spec:
  # replicas: not specified here:
  # 1. In order to make Addon Manager do not reconcile this replicas parameter.
  # 2. Default is 1.
  # 3. Will be tuned in real time if DNS horizontal auto-scaling is turned on.
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
  selector:
    matchLabels:
      k8s-app: kube-dns
  template:
    metadata:
      labels:
        k8s-app: kube-dns
      annotations:
        seccomp.security.alpha.kubernetes.io/pod: 'docker/default'
    spec:
      priorityClassName: system-cluster-critical
      serviceAccountName: coredns
      tolerations:
        - key: "CriticalAddonsOnly"
          operator: "Exists"
      nodeSelector:
        beta.kubernetes.io/os: linux
      containers:
      - name: coredns
        image: harbor.hzwod.com/k8s/coredns:1.6.5
        imagePullPolicy: IfNotPresent
        resources:
          limits:
            memory:  128Mi            # 内存限制
          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
        readinessProbe:
          httpGet:
            path: /ready
            port: 8181
            scheme: HTTP
        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

4.Service

coredns_service.yaml

apiVersion: v1
kind: Service
metadata:
  name: kube-dns
  namespace: kube-system
  annotations:
    prometheus.io/port: "9153"
    prometheus.io/scrape: "true"
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
    kubernetes.io/name: "CoreDNS"
spec:
  selector:
    k8s-app: kube-dns
  clusterIP: 192.168.0.2        # dns在集群中的ip
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP
  - name: metrics
    port: 9153
    protocol: TCP

clusterIP: 192.168.0.2指定coredns暴露svc的ip, 此ip要和 kubelet 启动参数--cluster-dns 192.168.0.2对应上

三.交付coredns

上述文件拷贝到node200:/data/k8s-yaml目录下

node21或node22上应用上述资源

kubectl apply -f http://k8s-yaml.hzwod.com/coredns_rbac.yaml
kubectl apply -f http://k8s-yaml.hzwod.com/coredns_configmap.yaml
kubectl apply -f http://k8s-yaml.hzwod.com/coredns_dp.yaml
kubectl apply -f http://k8s-yaml.hzwod.com/coredns_service.yaml

查看效果

[root@node21 ~]# kubectl get all -n kube-system 
NAME                           READY   STATUS    RESTARTS   AGE
pod/coredns-786565dc55-qpwpd   1/1     Running   0          <invalid>
NAME               TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)                  AGE
service/kube-dns   ClusterIP   192.168.0.2   <none>        53/UDP,53/TCP,9153/TCP   65m
NAME                      READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/coredns   1/1     1            1           99m
NAME                                 DESIRED   CURRENT   READY   AGE
replicaset.apps/coredns-786565dc55   1         1         1       99m
[root@node21 ~]# dig -t A nginx-dp.hzwns.svc.cluster.local. @192.168.0.2 +short
192.168.182.94

留下一个问题，看上图服务端nginx收到的数据包源地址不是容器ip，这个问题如何解决？