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基于ExternalDNS的多集群Ingress-DNS实践

jiezi

概要

External-DNS 提供了编程方式管理 Kubernetes Ingress 资源的 DNS 的功能，方便用户从 Ingress 管理 DNS 解析记录。而在 kubernetes federation v2 环境中，使用 External-DNS 可以快速的管理多个联邦集群的 Ingress DNS 解析，降低用户的操作成本。下面将简单介绍在阿里云容器服务环境中，如何使用 External-DNS 管理联邦集群的 Ingress DNS 解析。

联邦集群准备

参考阿里云 Kubernetes 容器服务上体验 Federation v2 搭建两个集群组成的联邦集群（配置好 kubeconfig，并完成两个集群的 join）。

配置 RAM 信息

选择 Kubernetes 集群节点列表内任意一个 Worker 节点，打开对应的节点列表信息页面。

找到对应的 RAM 角色，打开 RAM 控制台，找到对应的角色名称，添加【AliyunDNSFullAccess】权限。

注意： 每个集群都需要配置 RAM 信息 。

部署 External-DNS

配置 RBAC

执行下面 yaml：

apiVersion: v1
kind: ServiceAccount
metadata:
  name: external-dns
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
  name: external-dns
rules:
- apiGroups: [""]
  resources: ["services"]
  verbs: ["get","watch","list"]
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get","watch","list"]
- apiGroups: ["extensions"]
  resources: ["ingresses"]
  verbs: ["get","watch","list"]
- apiGroups: [""]
  resources: ["nodes"]
  verbs: ["list"]
- apiGroups: ["multiclusterdns.federation.k8s.io"]
  resources: ["dnsendpoints"]
  verbs: ["get", "watch", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: external-dns-viewer
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: external-dns
subjects:
- kind: ServiceAccount
  name: external-dns
  namespace: default

部署 External-DNS 服务

执行下面 yaml：

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: external-dns
spec:
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: external-dns
    spec:
      serviceAccountName: external-dns
      containers:
      - name: external-dns
        image: registry.cn-beijing.aliyuncs.com/acs/external-dns:v0.5.8-27
        args:
        - --source=crd
        - --crd-source-apiversion=multiclusterdns.federation.k8s.io/v1alpha1
        - --crd-source-kind=DNSEndpoint
        - --provider=alibabacloud
        - --policy=sync # enable full synchronization
        - --registry=txt
        - --txt-prefix=cname
        - --txt-owner-id=my-identifier
        - --alibaba-cloud-config-file= # enable sts token
        volumeMounts:
        - mountPath: /usr/share/zoneinfo
          name: hostpath
      volumes:
      - name: hostpath
        hostPath:
          path: /usr/share/zoneinfo
          type: Directory

部署验证资源

创建 FederatedDeployment 和 FederatedService：

apiVersion: v1
kind: Namespace
metadata:
  name: test-namespace

---

apiVersion: types.federation.k8s.io/v1alpha1
kind: FederatedNamespace
metadata:
  name: test-namespace
  namespace: test-namespace
spec:
  placement:
    clusterNames:
    - cluster1
    - cluster2

---

apiVersion: types.federation.k8s.io/v1alpha1
kind: FederatedDeployment
metadata:
  name: test-deployment
  namespace: test-namespace
spec:
  template:
    metadata:
      labels:
        app: nginx
    spec:
      replicas: 2
      selector:
        matchLabels:
          app: nginx
      template:
        metadata:
          labels:
            app: nginx
        spec:
          containers:
          - image: nginx
            name: nginx
            resources:
              limits:
                cpu: 500m
              requests:
                cpu: 200m
  placement:
    clusterNames:
    - cluster1
    - cluster2

---

apiVersion: types.federation.k8s.io/v1alpha1
kind: FederatedService
metadata:
  name: test-service
  namespace: test-namespace
spec:
  template:
    spec:
      selector:
        app: nginx
      type: ClusterIP
      ports:
        - name: http
          port: 80
  placement:
    clusterNames:
    - cluster2
    - cluster1

各个集群 ingress 创建信息如下：

kubectl get ingress -n test-namespace --context cluster1
NAME           HOSTS   ADDRESS        PORTS   AGE
test-ingress   *       47.93.69.121   80      54m

kubectl get ingress -n test-namespace --context cluster2
NAME           HOSTS   ADDRESS         PORTS   AGE
test-ingress   *       39.106.232.23   80      54m

创建 FederatedIngress 和 IngressDNSRecord

apiVersion: types.federation.k8s.io/v1alpha1
kind: FederatedIngress
metadata:
  name: test-ingress
  namespace: test-namespace
spec:
  template:
    spec:
       backend:
          serviceName: test-service
          servicePort: 80
  placement:
    clusterNames:
    - cluster2
    - cluster1        

---

apiVersion: multiclusterdns.federation.k8s.io/v1alpha1
kind: IngressDNSRecord
metadata:
  name: test-ingress
  namespace: test-namespace
spec:
  hosts:
  - ingress-example.example-domain.club
  recordTTL: 600

其中【ingress-example.example-domain.club】为测试阿里云托管的域名，请提前在阿里云上购买域名，并注意替换。

DNS 解析验证 

dig +short @dns7.hichina.com ingress-example.example-domain.club
47.93.69.121
39.106.232.23

可以看到我们绑定的域名已经解析到了 cluster1 和 cluster2 的 ingress IP 上了。
访问域名相应的服务：

curl ingress-example.sigma-host.club
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

总结

通过上面介绍，可以看到使用 External-DNS 可以非常方便的管理 federation-v2 环境下的 Ingress DNS 解析。

本文作者：钧博

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