基於External-DNS的多集羣Service DNS實踐
概述
External-DNS提供了編程方式管理Kubernetes Service資源的DNS的功能，類似於容器服務kubernetes federation v2實踐一：基於External-DNS的多集羣Ingress DNS實踐，External-DNS會監聽LoadBalancer類型的Service，然後與雲廠商打通，按照可用區、region和全局三個維度生成獨自的域名解析記錄，便於服務間調用引導流量。本文簡單介紹如何在阿里雲容器平臺上使用External-DNS管理多集羣Service DNS。
環境準備
參考容器服務kubernetes federation v2實踐一：基於External-DNS的多集羣Ingress DNS實踐完成【聯邦集羣準備】、【配置RAM信息】和【部署External-DNS】部分，並配置好kubeConfig，如下所示：
kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
* cluster1 cluster1 kubernetes-admin1
cluster2 cluster2 kubernetes-admin2
資源部署
創建FederatedDeployment和FederatedService
yaml如下，注意FederatedService類型為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
查看各個集羣Service詳情：
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
創建Domain和ServiceDNSRecord
yaml如下，注意請將【service.example-domain.club】替換成測試域名（必須由阿里雲託管的域名）。
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
結果分析
查看DnsEndpoint詳情：
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已經自動生成了4條解析記錄，包含北京兩個可用區、北京region和全局四個dns解析記錄。
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
結論
External-DNS在Federation-V2多集羣聯邦環境下，可以根據Service部署所在的可用區、region和全局三個維度生成多條DNS解析記錄，幫助服務靈活的引導流量。
本文作者：鈞博
原文鏈接
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