概述

External-DNS提供了编程方式管理Kubernetes Service资源的DNS的功能，类似于容器服务kubernetes federation v2实践一：基于External-DNS的多集群Ingress DNS实践-云栖社区-阿里云，External-DNS会监听LoadBalancer类型的Service，然后与云厂商打通，按照可用区、region和全局三个维度生成独自的域名解析记录，便于服务间调用引导流量。本文简单介绍如何在阿里云容器平台上使用External-DNS管理多集群Service DNS。

环境准备

参考容器服务kubernetes federation v2实践一：基于External-DNS的多集群Ingress DNS实践-云栖社区-阿里云完成【联邦集群准备】、【配置RAM信息】和【部署External-DNS】部分，并配置好kubeConfig，如下所示：

kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
* cluster1 cluster1 kubernetes-admin1
 cluster2 cluster2 kubernetes-admin2

资源部署

创建FederatedDeployment和FederatedService

yaml如下，注意FederatedService类型为LoadBalancer

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
 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: LoadBalancer
 ports:
 - name: http
 port: 80
 placement:
 clusterNames:
 - cluster2
 - cluster1

查看各个集群Service详情：

get svc -n test-namespace --context cluster1
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
test-service LoadBalancer 172.23.5.173 39.96.243.59 80:30185/TCP 28s
get svc -n test-namespace --context cluster2
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
test-service LoadBalancer 172.21.11.44 47.95.152.65 80:30384/TCP 31s

创建Domain和ServiceDNSRecord

yaml如下，注意请将【service.example-domain.club】替换成测试域名（必须由阿里云托管的域名）。

apiVersion: multiclusterdns.federation.k8s.io/v1alpha1
kind: Domain
metadata:
 name: test-domain
 namespace: federation-system
domain: service.example-domain.club
---
apiVersion: multiclusterdns.federation.k8s.io/v1alpha1
kind: ServiceDNSRecord
metadata:
 name: test-service
 namespace: test-namespace
spec:
 domainRef: test-domain
 recordTTL: 600

结果分析

查看DnsEndpoint详情：

kubectl get dnsendpoint -n test-namespace -o yaml
apiVersion: v1
items:
- apiVersion: multiclusterdns.federation.k8s.io/v1alpha1
 kind: DNSEndpoint
 metadata:
 creationTimestamp: 2019-05-17T08:49:31Z
 generation: 2
 name: service-test-service
 namespace: test-namespace
 resourceVersion: "742339863"
 selfLink: /apis/multiclusterdns.federation.k8s.io/v1alpha1/namespaces/test-namespace/dnsendpoints/service-test-service
 uid: afd3e22a-7880-11e9-9566-326dc52c25d3
 spec:
 endpoints:
 - dnsName: test-service.test-namespace.test-domain.svc.cn-beijing-a.cn-beijing.service.example-domain.club
 recordTTL: 600
 recordType: A
 targets:
 - 47.95.152.65
 - dnsName: test-service.test-namespace.test-domain.svc.cn-beijing-f.cn-beijing.service.example-domain.club
 recordTTL: 600
 recordType: A
 targets:
 - 39.96.243.59
 - dnsName: test-service.test-namespace.test-domain.svc.cn-beijing.service.example-domain.club
 recordTTL: 600
 recordType: A
 targets:
 - 39.96.243.59
 - 47.95.152.65
 - dnsName: test-service.test-namespace.test-domain.svc.service.example-domain.club
 recordTTL: 600
 recordType: A
 targets:
 - 39.96.243.59
 - 47.95.152.65
kind: List
metadata:
 resourceVersion: ""
 selfLink: ""

可以看到External-DNS已经自动生成了4条解析记录，包含北京两个可用区、北京region和全局四个dns解析记录。

dig +short @dns7.hichina.com test-service.test-namespace.test-domain.svc.cn-beijing-a.cn-beijing.service.example-domain.club
47.95.152.65
dig +short @dns7.hichina.com test-service.test-namespace.test-domain.svc.cn-beijing-f.cn-beijing.service.example-domain.club
39.96.243.59
dig +short @dns7.hichina.com test-service.test-namespace.test-domain.svc.cn-beijing.service.example-domain.club
47.95.152.65
39.96.243.59
dig +short @dns7.hichina.com test-service.test-namespace.test-domain.svc.service.example-domain.club
47.95.152.65
39.96.243.59

结论

External-DNS在Federation-V2多集群联邦环境下，可以根据Service部署所在的可用区、region和全局三个维度生成多条DNS解析记录，帮助服务灵活的引导流量。

作者：钧博