ExternalDNS with Designate

To reduce manual effort and automate the configuration of DNS zones, you may want to use ExternalDNS. In summary, ExternalDNS allows you to control DNS records dynamically with Kubernetes resources in a DNS provider-agnostic way. ExternalDNS is not a DNS server by itself, but merely configures other DNS providers (for example, OpenStack Designate, Amazon Route53, Google Cloud DNS, and so on.)

Prerequisites

To successfully complete the following steps, you need the following:

kubectl latest version
A running Kubernetes cluster created with GKS, with a ready Machine Deployment
- For more information, see Creating a Cluster.
A valid kubeconfig for your cluster
- For more information, see Connecting to a Cluster.
Installed OpenStack CLI tools
OpenStack API access
A valid domain

Configuring Your Domain to Use Designate

Delegate your domains from your DNS provider to the following GEC DNS name servers so that Designate can control the DNS resources of your domain.

dns1.ddns.innovo.cloud
dns2.ddns.innovo.cloud

Creating your DNS Zone

Before you use ExternalDNS, you need to add your DNS zones to your DNS provider, in this case, Designate DNS.

In our example we use the test domain name foobar.cloud. It is important to create the zones before starting to control the DNS resources with Kubernetes.

Note: You must include the final . at the end of the zone/domain to be created.

$ openstack zone create --email webmaster@foobar.cloud foobar.cloud.
+----------------+--------------------------------------+
| Field          | Value                                |
+----------------+--------------------------------------+
| action         | CREATE                               |
| attributes     |                                      |
| created_at     | 2018-08-15T06:45:24.000000           |
| description    | None                                 |
| email          | webmaster@foobar.cloud               |
| id             | 036ae6e6-6318-47e1-920f-be518d845fb5 |
| masters        |                                      |
| name           | foobar.cloud.                        |
| pool_id        | bb031d0d-b8ca-455a-8963-50ec70fe57cf |
| project_id     | 2b62bc8ff48445f394d0318dbd058967     |
| serial         | 1534315524                           |
| status         | PENDING                              |
| transferred_at | None                                 |
| ttl            | 3600                                 |
| type           | PRIMARY                              |
| updated_at     | None                                 |
| version        | 1                                    |
+----------------+--------------------------------------+

Next, make sure that the zone was created successfully.

$ openstack zone list
+--------------------------------------+-----------------------+---------+------------+--------+--------+
| id                                   | name                  | type    |     serial | status | action |
+--------------------------------------+-----------------------+---------+------------+--------+--------+
| 036ae6e6-6318-47e1-920f-be518d845fb5 | foobar.cloud.         | PRIMARY | 1534315524 | ACTIVE | NONE   |
+--------------------------------------+-----------------------+---------+------------+--------+--------+

$ openstack zone show foobar.cloud.
+----------------+--------------------------------------+
| Field          | Value                                |
+----------------+--------------------------------------+
| action         | NONE                                 |
| attributes     |                                      |
| created_at     | 2018-08-15T06:45:24.000000           |
| description    | None                                 |
| email          | webmaster@foobar.cloud               |
| id             | 036ae6e6-6318-47e1-920f-be518d845fb5 |
| masters        |                                      |
| name           | foobar.cloud.                        |
| pool_id        | bb031d0d-b8ca-455a-8963-50ec70fe57cf |
| project_id     | 2b62bc8ff48445f394d0318dbd058967     |
| serial         | 1534315524                           |
| status         | ACTIVE                               |
| transferred_at | None                                 |
| ttl            | 3600                                 |
| type           | PRIMARY                              |
| updated_at     | 2018-08-15T06:45:30.000000           |
| version        | 2                                    |
+----------------+--------------------------------------+

Installing ExternalDNS with Helm

Install ExternalDNS to your cluster. In our example we will use Helm as follows:

Install Helm
$ helm repo add stable https://kubernetes-charts.storage.googleapis.com/
$ helm repo update
Create this values.yaml file and configure it. For more information, see values-external-dns.

## K8s resources type to be observed for new DNS entries by ExternalDNS
##
sources:
  - service
  - ingress

## DNS provider where the DNS records will be created. Available providers are:
## - aws, azure, cloudflare, coredns, designate, digitalocoean, google, infoblox, rfc2136, transip
##
provider: designate

## Adjust the interval for DNS updates
##
interval: "1m"

## Registry Type. Available types are: txt, noop
## ref: https://github.com/kubernetes-incubator/external-dns/blob/master/docs/proposal/registry.md
##
registry: "txt"

## TXT Registry Identifier, a name that identifies this instance of External-DNS
## This value should not change, while the cluster exists
##
txtOwnerId: "external-dns"

## Modify how DNS records are sychronized between sources and providers (options: sync, upsert-only )
##
policy: sync

## Configure resource requests and limits
## ref: http://kubernetes.io/docs/user-guide/compute-resources/
##
resources:
  limits:
    memory: 50Mi
    cpu: 10m
  requests:
    memory: 50Mi
    cpu: 10m
## Configure your OS Access
##
extraEnv:
  - name: OS_AUTH_URL
    value: https://identity.optimist.gec.io/v3
  - name: OS_REGION_NAME
    value: fra
  - name: OS_USERNAME
    value: "%YOUR_OPENSTACK_USERNAME%"
  - name: OS_PASSWORD
    value: "%YOUR_OPENSTACK_PASSWORD%"
  - name: OS_PROJECT_NAME
    value: "%YOUR_OPENSTACK_PROJECT_NAME%"
  - name: OS_USER_DOMAIN_NAME
    value: Default

$ kubectl create namespace external-dns
$ helm upgrade --install external-dns -f values.yaml stable/external-dns --namespace=external-dns

Running Your Deployment

To test the fully-qualified domain name (FQDN) of the domain, create this example deployment as nginx.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    external-dns.alpha.kubernetes.io/hostname: nginx.foobar.cloud
    external-dns.alpha.kubernetes.io/ttl: "60"
spec:
  selector:
    app: nginx
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

Apply the configuration to your cluster with:

kubectl apply -f nginx.yaml

Confirming the Results

Check your DNS resources in OpenStack. You should see a similar list with the corresponding DNS records.

openstack recordset list foobar.cloud.

Wait a few minutes, and then test the availability over the internet. For example, browse to your website. You should see the following in your browser.

nginx

Summary

By completing these steps, you’ve accomplished the following:

Learned what ExternalDNS is and how to install it
Configured ExternalDNS with Helm to use Designate
Created a deployment with NGINX and tested the connectivity

Congratulations! You now know all required steps to control your DNS resources in Kubernetes.