# Setting up ExternalDNS on Google Container Engine

This tutorial describes how to setup ExternalDNS for usage within a GKE cluster.

Setup your environment to work with Google Cloud Platform. Fill in your values as needed, e.g. target project.

```console
$ gcloud config set project "zalando-external-dns-test"
$ gcloud config set compute/region "europe-west1"
$ gcloud config set compute/zone "europe-west1-d"
```

Create a GKE cluster.

```console
$ gcloud container clusters create "external-dns" \
    --num-nodes 1 \
    --scopes "https://www.googleapis.com/auth/ndev.clouddns.readwrite"
```

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

```console
$ gcloud dns managed-zones create "external-dns-test-gcp-zalan-do" \
    --dns-name "external-dns-test.gcp.zalan.do." \
    --description "Automatically managed zone by kubernetes.io/external-dns"
```

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

```console
$ gcloud dns record-sets list \
    --zone "external-dns-test-gcp-zalan-do" \
    --name "external-dns-test.gcp.zalan.do." \
    --type NS
NAME                             TYPE  TTL    DATA
external-dns-test.gcp.zalan.do.  NS    21600  ns-cloud-e1.googledomains.com.,ns-cloud-e2.googledomains.com.,ns-cloud-e3.googledomains.com.,ns-cloud-e4.googledomains.com.
```

In this case it's `ns-cloud-{e1-e4}.googledomains.com.` but your's could slightly differ, e.g. `{a1-a4}`, `{b1-b4}` etc.

Tell the parent zone where to find the DNS records for this zone by adding the corresponding NS records there. Assuming the parent zone is "gcp-zalan-do" and the domain is "gcp.zalan.do" and that it's also hosted at Google we would do the following.

```console
$ gcloud dns record-sets transaction start --zone "gcp-zalan-do"
$ gcloud dns record-sets transaction add ns-cloud-e{1..4}.googledomains.com. \
    --name "external-dns-test.gcp.zalan.do." --ttl 300 --type NS --zone "gcp-zalan-do"
$ gcloud dns record-sets transaction execute --zone "gcp-zalan-do"
```

If you decide not to create a new zone but reuse an existing one, make sure it's currently **unused** and **empty**. This version of ExternalDNS will remove all records it doesn't recognize from the zone.

Connect your `kubectl` client to the cluster you just created.

```console
gcloud container clusters get-credentials "external-dns"
```

Apply the following manifest file to deploy ExternalDNS.

```yaml
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:v0.2.1
        args:
        - --in-cluster
        - --zone=external-dns-test-gcp-zalan-do
        - --source=service
        - --source=ingress
        - --provider=google
        - --google-project=zalando-external-dns-test
        - --dry-run=false
```

Use `dry-run=true` if you want to be extra careful on the first run. Note, that you will not see any records created when you are running in dry-run mode. You can, however, inspect the logs and watch what would have been done.

Create the following sample application to test that ExternalDNS works.

```yaml
apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.gcp.zalan.do.
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.

```console
$ gcloud dns record-sets list \
    --zone "external-dns-test-gcp-zalan-do" \
    --name "nginx.external-dns-test.gcp.zalan.do." \
    --type A
NAME                                   TYPE  TTL  DATA
nginx.external-dns-test.gcp.zalan.do.  A     300  104.155.60.49
```

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

```console
$ dig +short @ns-cloud-e1.googledomains.com. nginx.external-dns-test.gcp.zalan.do.
104.155.60.49
```

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

```console
$ curl nginx.external-dns-test.gcp.zalan.do
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...
</head>
<body>
...
</body>
</html>
```

Let's check that Ingress works as well. Create the following Ingress.

```yaml
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: nginx
spec:
  rules:
  - host: via-ingress.external-dns-test.gcp.zalan.do
    http:
      paths:
      - backend:
          serviceName: nginx
          servicePort: 80
```

Again, after roughly two minutes check that a corresponding DNS record for your Ingress was created.

```console
$ gcloud dns record-sets list \
    --zone "external-dns-test-gcp-zalan-do" \
    --name "via-ingress.external-dns-test.gcp.zalan.do." \
    --type A
NAME                                         TYPE  TTL  DATA
via-ingress.external-dns-test.gcp.zalan.do.  A     300  130.211.46.224
```

Let's check that we can resolve this DNS name as well.

```console
dig +short @ns-cloud-e1.googledomains.com. via-ingress.external-dns-test.gcp.zalan.do.
130.211.46.224
```

Try with `curl` as well.

```console
$ curl via-ingress.external-dns-test.gcp.zalan.do
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...
</head>
<body>
...
</body>
</html>
```

## Clean up

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

```console
$ kubectl delete service nginx
$ kubectl delete ingress nginx
```

Give ExternalDNS some time to clean up the DNS records for you. Then delete the managed zone and cluster.

```console
$ gcloud dns managed-zones delete "external-dns-test-gcp-zalan-do"
$ gcloud container clusters delete "external-dns"
```

Also delete the NS records for your removed zone from the parent zone.

```console
$ gcloud dns record-sets transaction start --zone "gcp-zalan-do"
$ gcloud dns record-sets transaction remove ns-cloud-e{1..4}.googledomains.com. \
    --name "external-dns-test.gcp.zalan.do." --ttl 300 --type NS --zone "gcp-zalan-do"
$ gcloud dns record-sets transaction execute --zone "gcp-zalan-do"
```