Document external-dns configuration

[tamalsaha]

For all 3 modes.
https://github.com/kubernetes-incubator/external-dns

[tamalsaha]

ingress.appscode.com/type: LoadBalancer
For a LoadBlanacer type Ingress, you apply "external-dns.alpha.kubernetes.io/hostname" annotation on the service that exposes HAProxy pods.

apiVersion: voyager.appscode.com/v1beta1
kind: Ingress
metadata:
  name: test-ingress-voyager
  namespace: vdimov-dev
  annotations:
     ingress.appscode.com/annotations-service: |
         {
           "external-dns.alpha.kubernetes.io/hostname" : "voyager.example.com,voyager-1.example.com,voyager-2.example.com"
         }
     ingress.appscode.com/replicas: '2'
spec:
  rules:
  - host: voyager.example.com
    http:
      paths:
       - backend:
          serviceName: web
          servicePort: '80'

ingress.appscode.com/type: HostPort
This is only supported by legacy kops controller. external-dns project has recently added support for headless service. There is no release with that commit yet.

• Requires:
• Avoid missing pod hostname for headless service kubernetes-sigs/external-dns#429
• Add support for Headless hostPort services kubernetes-sigs/external-dns#324
  This has to be build from master Feb 18, 2018

- kubernetes-sigs/external-dns#195
- kubernetes-sigs/external-dns#221

For a HostPort type Ingress, you apply "external-dns.alpha.kubernetes.io/hostname" annotation on the pods that exposes HAProxy pods.

apiVersion: voyager.appscode.com/v1beta1
kind: Ingress
metadata:
  name: test-ingress-voyager
  namespace: vdimov-dev
  annotations:
     ingress.appscode.com/type: HostPort
     ingress.appscode.com/annotations-pod: |
         {
           "external-dns.alpha.kubernetes.io/hostname" : "voyager.example.com,voyager-1.example.com,voyager-2.example.com"
         }
     ingress.appscode.com/replicas: '2'
spec:
  rules:
  - host: voyager.example.com
    http:
      paths:
       - backend:
          serviceName: web
          servicePort: '80'

ingress.appscode.com/type: NodePort
external-dns is not supported in this mode.

[sheerun]

Can't extenral-dns recognize ingress resources?

[tamalsaha]

If you use Voyager defined CRDs (apiVersion: voyager.appscode.com/v1beta1), external-dns can't automatically detect Intgress. You have to use the ingress.appscode.com/annotations-service annotation so that external-dns can pick the necessary info from the Service used to expose HAProxy pods.

[sheerun]

Can't Voyager automatically set these annotations on its service? It has access to ingress hosts so in the example above it can generate at least external-dns.alpha.kubernetes.io/hostname: "voyager.example.com"

[tamalsaha]

The issue is voyager does not know if user is using external-dns, whether external-dns supports user's DNS provider etc. So, we left it a manual setup on Ingress YAML.

[sheerun]

Unfortunately it is a chore to write above for every ingress. It would be far more convenient if I could set externalDnsIntegration: true in values.yaml and voyager generated these for me :)

[sheerun]

Of course extra documentation is also fine, but external-dns seems to be the tool of choice, it's good to integrate with it.

[tamalsaha]

I hear you! We will look into this. This is not a priority for the moment.

[tamalsaha]

#895