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Setting up ExternalDNS for Services on AWS

This tutorial describes how to setup ExternalDNS for usage within a Kubernetes cluster on AWS. Make sure to use >=0.4 version of ExternalDNS for this tutorial

IAM Permissions

{
 "Version": "2012-10-17",
 "Statement": [
   {
     "Effect": "Allow",
     "Action": [
       "route53:ChangeResourceRecordSets"
     ],
     "Resource": [
       "arn:aws:route53:::hostedzone/*"
     ]
   },
   {
     "Effect": "Allow",
     "Action": [
       "route53:ListHostedZones",
       "route53:ListResourceRecordSets"
     ],
     "Resource": [
       "*"
     ]
   }
 ]
}

Set up a hosted zone

If you prefer to try-out ExternalDNS in one of the existing hosted-zones you can skip this step

Create a DNS zone which will contain the managed DNS records.

$ aws route53 create-hosted-zone --name "external-dns-test.my-org.com." --caller-reference "external-dns-test-$(date +%s)"

Make a note of the ID of the hosted zone you just created.

$ aws route53 list-hosted-zones-by-name --dns-name "external-dns-test.my-org.com." | jq -r '.HostedZones[0].Id'
/hostedzone/ZEWFWZ4R16P7IB

Make a note of the nameservers that were assigned to your new zone.

$ aws route53 list-resource-record-sets --hosted-zone-id "/hostedzone/ZEWFWZ4R16P7IB" \
    --query "ResourceRecordSets[?Type == 'NS']" | jq -r '.[0].ResourceRecords[].Value'
ns-5514.awsdns-53.org.
...

In this case it's the ones shown above but your's will differ.

Deploy ExternalDNS

Connect your kubectl client to the cluster you want to test ExternalDNS with. Then apply the following manifest file to deploy ExternalDNS.

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: external-dns
spec:
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: external-dns
    spec:
      containers:
      - name: external-dns
        image: registry.opensource.zalan.do/teapot/external-dns:v0.4.2
        args:
        - --source=service
        - --source=ingress
        - --domain-filter=external-dns-test.my-org.com # will make ExternalDNS see only the hosted zones matching provided domain, omit to process all available hosted zones
        - --provider=aws
        - --policy=upsert-only # would prevent ExternalDNS from deleting any records, omit to enable full synchronization
        - --registry=txt
        - --txt-owner-id=my-identifier

Verify ExternalDNS works

Create the following sample application to test that ExternalDNS works.

apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com.
spec:
  type: LoadBalancer
  ports:
  - port: 80
    targetPort: 80
  selector:
    app: nginx

---

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx
spec:
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80

After roughly two minutes check that a corresponding DNS record for your service was created.

$ aws route53 list-resource-record-sets --hosted-zone-id "/hostedzone/ZEWFWZ4R16P7IB" \
    --query "ResourceRecordSets[?Name == 'nginx.external-dns-test.my-org.com.']|[?Type == 'A']"
[
    {
      "AliasTarget": {
          "HostedZoneId": "ZEWFWZ4R16P7IB",
          "DNSName": "ae11c2360188411e7951602725593fd1-1224345803.eu-central-1.elb.amazonaws.com.",
          "EvaluateTargetHealth": true
      },
      "Name": "external-dns-test.my-org.com.",
      "Type": "A"
    },
    {
      "Name": "external-dns-test.my-org.com",
      "TTL": 300,
      "ResourceRecords": [
          {
              "Value": "\"heritage=external-dns,external-dns/owner=my-identifier\""
          }
      ],
      "Type": "TXT"
    }
]

Note created TXT record alongside ALIAS record. TXT record signifies that the corresponding ALIAS record is managed by ExternalDNS. This makes ExternalDNS safe for running in environments where there are other records managed via other means.

Let's check that we can resolve this DNS name. We'll ask the nameservers assigned to your zone first.

$ dig +short @ns-5514.awsdns-53.org. nginx.external-dns-test.my-org.com.
ae11c2360188411e7951602725593fd1-1224345803.eu-central-1.elb.amazonaws.com.

If you hooked up your DNS zone with its parent zone correctly you can use curl to access your site.

$ curl nginx.external-dns-test.my-org.com.
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...
</head>
<body>
...
</body>
</html>

Ingress objects on AWS require a separately deployed Ingress controller which we'll describe in another tutorial.

Custom TTL

The default DNS record TTL (Time-To-Live) is 300 seconds. You can customize this value by setting the annotation external-dns.alpha.kubernetes.io/ttl. e.g., modify the service manifest YAML file above:

apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com.
    external-dns.alpha.kubernetes.io/ttl: 60
spec:
    ...

This will set the DNS record's TTL to 60 seconds.

Clean up

Make sure to delete all Service objects before terminating the cluster so all load balancers get cleaned up correctly.

$ kubectl delete service nginx

Give ExternalDNS some time to clean up the DNS records for you. Then delete the hosted zone if you created one for the testing purpose.

$ aws route53 delete-hosted-zone --id /hostedzone/ZEWFWZ4R16P7IB