使用ExternalDNS自动化DNS配置

Kubernetes社区的生态繁荣和该领域技术的快速茁壮发展，已经是众所周知。Kubernetes领域有太多强大的、创新的技术产品，而最近引起我注意的项目是ExternalDNS。这是在近期的POC期间客户主动咨询起来的，我承诺客户会尝试一下ExternalDNS子项目，且使用后发现它真的令人印象深刻。

ExternalDNS子项目

ExternalDNS子项目（孵化器流程已被弃用）是由sig-network赞助并由Tim Hockin倡导的，旨在自动配置云DNS提供商。这很重要，因为它进一步支持基础架构自动化，用户可以在应用程序部署的同时直接完成DNS配置。

传统企业部署模型，通常是由多个孤立业务单元，来处理部署过程的不同部分。但带有ExternalDNS的Kubernetes不同于传统企业部署模型，它可以自动完成此过程的这一部分工作。有时候有可能会出现这种不好的情况：一部分软件已准备就绪，但它却必须等待另一个业务部门手动配置DNS。而有了ExternalDNS，这一潜在问题就被解决了。

通过ExternalDNS，组织团队可实现自动化和共同责任协作，而这将避免手动配置的错误，并使各方都能够更有效地将其产品推向市场。

AKS上的ExternalDNS配置和部署

我曾作为软件开发人员在.NET领域有过多年的工作经验。微软开发人员社区在我心中一直有一个特殊的位置，过去几年以来我参加过不少费城地区的Azure用户meetup，分享如何通过ACS（Azure Container Service）和AKS（Azure Kubernetes Service）使用Kubernetes on Azure。恰巧的是，向我咨询ExternalDNS的用户也正是在选择了Azure作为其IaaS产品。

下文是我准备的在AKS集群上启动ExternalDNS的分步说明和帮助程序代码。即使您使用的是其他公有云上的托管的Kubernetes，本教程依然适用。

先决条件

登录Azure AD，必要情况下请设置订阅。

几点注意事项

1、请注意，本文档中的外部模板文件使用了许多可选设置。

2、它也在debug级别日志中，因此您也可以自行进行troubleshooting。

在Azure AKS或Azure IaaS上设置ExternalDNS

1、创建Azure DNS记录

RESOURCE_GROUP=MC_rancher-group_c-6vkts_eastus
DNS_ZONE=vanbrackel.net
az network dns zone create -g $RESOURCE_GROUP -n $DNS_ZONE
2、根据您的注册商的需要委派DNS

3、创建服务主体以代表Kubernetes行事。

SUBSCRIPTION_id="$(az account show | jq '.id')" && SUBSCRIPTION_ID=${SUBSCRIPTION_ID//"}
TENANT_ID=$(az account show | jq '.tenantId') && TENANT_ID=${TENANT_ID//"}
SCOPE=$(az group show --name $RESOURCE_GROUP | jq '.id') && SCOPE=${SCOPE//"}
PRINCIPAL=$(az ad sp create-for-rbac --role="Contributor" --scopes=$SCOPE -n ExternalDnsServicePrincipal)
CLIENT_ID=$(echo $PRINCIPAL | jq '.appId') && CLIENT_ID=${CLIENT_ID//"}
CLIENT_SECRET=$(echo $PRINCIPAL | jq '.password') && CLIENT_SECRET=${CLIENT_SECRET//"}
4、创建你的云提供商配置。

echo "{ "tenantId": "$TENANT_ID\", \"subscriptionId\": \"$SUBSCRIPTION_ID", "aadClientId": "$CLIENT_ID\", \"aadClientSecret\": \"$CLIENT_SECRET", "resourceGroup": "$RESOURCE_GROUP"}" >> azure.json
5、使用云提供商配置来创建一个Kubernetes秘钥。

kubectl create secret generic azure-config-file --from-file=azure.json
secret "azure-config-file" created
6、如果你使用的是Rancher配置的Azure IaaS Backed Clusters，从集群中删除ingress controller。

kubectl get ns
NAME STATUS AGE
cattle-system Active 1d
default Active 1d
ingress-nginx Active 1d
kube-public Active 1d
kube-system Active 1d
kubectl delete ns/ingress-nginx
namespace "ingress-nginx" deleted
注意：如果您是使用Rancher中的 AKS配置的集群，则不会提供ingress controller。

7、安装nginx ingress controller并为ExternalDNS配置它。创建ingress-nginx部署和服务。

kubectl apply -f https://raw.githubusercontent...
kubectl apply -f https://raw.githubusercontent...
8、由于在基于Rancher的Kubernetes集群上默认启用了RBAC，因此可以从下面的脚本创建名为externaldns.yaml的yaml文件，或者使用此repo中的externaldns-template.yaml文件。

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"]

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

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.opensource.zalan.do/teapot/external-dns:v0.5.2
    args:
    - --source=service
    - --source=ingress
    - --domain-filter=vanbrackel.net # (optional) limit to only vanbrackel.net domains; change to match the zone created above.
    - --provider=azure
    - --azure-resource-group=MC_rancher-group_c-6vkts_eastus # (optional) use the DNS zones from above
    volumeMounts:
    - name: azure-config-file
      mountPath: /etc/kubernetes
      readOnly: true
  volumes:
  - name: azure-config-file
    secret:
      secretName: azure-config-file

EXTERNAL_DNS=$(cat externaldns-template.yaml)
EXTERNAL_DNS=${EXTERNAL_DNS//DOMAIN/$DOMAIN} && echo "${EXTERNAL_DNS//RESOURCE_GROUP/$RESOURCE_GROUP}" >> externaldns.yaml
kubectl create -f externaldns.yaml
验证
1、以与部署ExternalDNS相同的方式在ingress中创建nginx服务

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: nginx
spec:
template:

metadata:
  labels:
    app: nginx
spec:
  containers:
  - image: nginx
    name: nginx
    ports:
    - containerPort: 80

apiVersion: v1
kind: Service
metadata:
name: nginx-svc
spec:
ports:

port: 80
protocol: TCP
targetPort: 80

selector:

app: nginx

type: ClusterIP

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
name: nginx
annotations:

kubernetes.io/ingress.class: nginx

spec:
rules:

host: server.vanbrackel.net
http:

paths:
- backend:
    serviceName: nginx-svc
    servicePort: 80
  path: /

NGINX=$(cat nginx-ingress-test-template.yaml) && echo "${NGINX//DOMAIN/$DOMAIN}" >> nginx-ingress-test.yaml
2、创建nginx-ingress controller

kubectl create -f nginx-ingress-test.yaml
3、稍等几分钟

4、检查一下是否已有record被创建出来

[jason@vblinux ~ ]$ az network dns record-set a list --resource-group $RESOURCE_GROUP --zone-name $DNS_ZONE
[
{

"arecords": [
  {
    "ipv4Address": "13.68.138.206"
  }
],
"etag": "0fb3eaf9-7bf2-48c4-b8f8-432e05dce94a",
"fqdn": "server.vanbrackel.net.",
"id": "/subscriptions/c7e23d24-5dcd-4c7c-ae84-22f6f814dc02/resourceGroups/mc_rancher-group_c-6vkts_eastus/providers/Microsoft.Network/dnszones/vanbrackel.net/A/server",
"metadata": null,
"name": "server",
"resourceGroup": "mc_rancher-group_c-6vkts_eastus",
"ttl": 300,
"type": "Microsoft.Network/dnszones/A"

}
]
5、检查日志

kubectl logs external-dns-655df89959-7ztm2 
time="2018-06-13T23:57:11Z" level=info msg="config: {Master: KubeConfig: Sources:[service ingress] Namespace: AnnotationFilter: FQDNTemplate: CombineFQDNAndAnnotation:false Compatibility: PublishInternal:false ConnectorSourceServer:localhost:8080 Provider:azure GoogleProject: DomainFilter:[vanbrackel.net] ZoneIDFilter:[] AWSZoneType: AWSAssumeRole: AzureConfigFile:/etc/kubernetes/azure.json AzureResourceGroup:MC_rancher-group_c-6vkts_eastus CloudflareProxied:false InfobloxGridHost: InfobloxWapiPort:443 InfobloxWapiUsername:admin InfobloxWapiPassword: InfobloxWapiVersion:2.3.1 InfobloxSSLVerify:true DynCustomerName: DynUsername: DynPassword: DynMinTTLSeconds:0 InMemoryZones:[] PDNSServer:http://localhost:8081 PDNSAPIKey: Policy:sync Registry:txt TXTOwnerID:default TXTPrefix: Interval:1m0s Once:false DryRun:false LogFormat:text MetricsAddress::7979 LogLevel:debug}"
time="2018-06-13T23:57:11Z" level=info msg="Connected to cluster at https://10.0.0.1:443"
...
time="2018-06-14T00:02:11Z" level=debug msg="Retrieving Azure DNS zones."
time="2018-06-14T00:02:12Z" level=debug msg="Found 1 Azure DNS zone(s)."
time="2018-06-14T00:02:12Z" level=debug msg="Retrieving Azure DNS records for zone 'vanbrackel.net'."
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service default/kubernetes"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service default/nginx-svc"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service ingress-nginx/default-http-backend"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service ingress-nginx/ingress-nginx"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service kube-system/full-guppy-nginx-ingress-controller" time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service kube-system/full-guppy-nginx-ingress-default-backend"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service kube-system/heapster"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service kube-system/kube-dns"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service kube-system/kubernetes-dashboard"
time="2018-06-14T00:02:12Z" level=debug msg="No endpoints could be generated from service kube-system/tiller-deploy"
time="2018-06-14T00:02:12Z" level=debug msg="Endpoints generated from ingress: default/nginx: [server.vanbrackel.net 0 IN A 13.68.138.206]"
time="2018-06-14T00:02:12Z" level=debug msg="Retrieving Azure DNS zones."
time="2018-06-14T00:02:12Z" level=debug msg="Found 1 Azure DNS zone(s)."
time="2018-06-14T00:02:12Z" level=info msg="Updating A record named 'server' to '13.68.138.206' for Azure DNS zone 'vanbrackel.net'."
time="2018-06-14T00:02:13Z" level=info msg="Updating TXT record named 'server' to '\"heritage=external-dns,external-dns/owner=default,external-dns/resource=ingress/default/nginx\"' for Azure DNS zone 'vanbrackel.net'."
time="2018-06-14T00:03:11Z" level=debug msg="Retrieving Azure DNS zones."
time="2018-06-14T00:03:12Z" level=debug msg="Found 1 Azure DNS zone(s)."
time="2018-06-14T00:03:12Z" level=debug msg="Retrieving Azure DNS records for zone 'vanbrackel.net'."
time="2018-06-14T00:03:12Z" level=debug msg="Found A record for 'server.vanbrackel.net' with target '13.68.138.206'."
time="2018-06-14T00:03:12Z" level=debug msg="Found TXT record for 'server.vanbrackel.net' with target '\"heritage=external-dns,external-dns/owner=default,external-dns/resource=ingress/default/nginx\"'."
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service default/kubernetes"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service default/nginx-svc" time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service ingress-nginx/default-http-backend"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service ingress-nginx/ingress-nginx"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service kube-system/full-guppy-nginx-ingress-controller"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service kube-system/full-guppy-nginx-ingress-default-backend"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service kube-system/heapster"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service kube-system/kube-dns"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service kube-system/kubernetes-dashboard"
time="2018-06-14T00:03:12Z" level=debug msg="No endpoints could be generated from service kube-system/tiller-deploy"
time="2018-06-14T00:03:12Z" level=debug msg="Endpoints generated from ingress: default/nginx: [server.vanbrackel.net 0 IN A 13.68.138.206]"
time="2018-06-14T00:03:12Z" level=debug msg="Retrieving Azure DNS zones."
time="2018-06-14T00:03:12Z" level=debug msg="Found 1 Azure DNS zone(s)."

您还可以在ExternalDNS的repo中了解更多信息：

https://github.com/kubernetes...

如希望对原文中的代码有更深入的了解，请猛戳这里：

https://github.com/JasonvanBr...

使用ExternalDNS自动化DNS配置

name: external-dns

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