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Using ExternalDNS with kube-ingress-aws-controller

This tutorial describes how to use ExternalDNS with the kube-ingress-aws-controller.

Setting up ExternalDNS and kube-ingress-aws-controller

Follow the AWS tutorial to setup ExternalDNS for use in Kubernetes clusters running in AWS. Specify the source=ingress argument so that ExternalDNS will look for hostnames in Ingress objects. In addition, you may wish to limit which Ingress objects are used as an ExternalDNS source via the ingress-class argument, but this is not required.

For help setting up the Kubernetes Ingress AWS Controller, that can create ALBs and NLBs, follow the Setup Guide.

Optional RouteGroup

RouteGroup is a CRD, that enables you to do complex routing with Skipper.

First, you have to apply the RouteGroup CRD to your cluster:

kubectl apply -f https://github.com/zalando/skipper/blob/HEAD/dataclients/kubernetes/deploy/apply/routegroups_crd.yaml

You have to grant all controllers: Skipper, kube-ingress-aws-controller and external-dns to read the routegroup resource and kube-ingress-aws-controller to update the status field of a routegroup. This depends on your RBAC policies, in case you use RBAC, you can use this for all 3 controllers:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: kube-ingress-aws-controller
rules:
- apiGroups:
  - extensions
  - networking.k8s.io
  resources:
  - ingresses
  verbs:
  - get
  - list
  - watch
- apiGroups:
  - extensions
  - networking.k8s.io
  resources:
  - ingresses/status
  verbs:
  - patch
  - update
- apiGroups:
  - zalando.org
  resources:
  - routegroups
  verbs:
  - get
  - list
  - watch
- apiGroups:
  - zalando.org
  resources:
  - routegroups/status
  verbs:
  - patch
  - update

See also current RBAC yaml files:

Deploy an example application

Create the following sample "echoserver" application to demonstrate how ExternalDNS works with ingress objects, that were created by kube-ingress-aws-controller.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: echoserver
spec:
  replicas: 1
  selector:
    matchLabels:
      app: echoserver
  template:
    metadata:
      labels:
        app: echoserver
    spec:
      containers:
      - image: gcr.io/google_containers/echoserver:1.4
        imagePullPolicy: Always
        name: echoserver
        ports:
        - containerPort: 8080
---
apiVersion: v1
kind: Service
metadata:
  name: echoserver
spec:
  ports:
    - port: 80
      targetPort: 8080
      protocol: TCP
  type: ClusterIP
  selector:
    app: echoserver

Note that the Service object is of type ClusterIP, because we will target Skipper and do the HTTP routing in Skipper. We don't need a Service of type LoadBalancer here, since we will be using a shared skipper-ingress for all Ingress. Skipper use hostNetwork to be able to get traffic from AWS LoadBalancers EC2 network. ALBs or NLBs, will be created based on need and will be shared across all ingress as default.

Ingress examples

Create the following Ingress to expose the echoserver application to the Internet.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    kubernetes.io/ingress.class: skipper
  name: echoserver
spec:
  rules:
  - host: echoserver.mycluster.example.org
    http: &echoserver_root
      paths:
      - backend:
          serviceName: echoserver
          servicePort: 80
        path: /
  - host: echoserver.example.org
    http: *echoserver_root

The above should result in the creation of an (ipv4) ALB in AWS which will forward traffic to skipper which will forward to the echoserver application.

If the --source=ingress argument is specified, then ExternalDNS will create DNS records based on the hosts specified in ingress objects. The above example would result in two alias records being created, echoserver.mycluster.example.org and echoserver.example.org, which both alias the ALB that is associated with the Ingress object.

Note that the above example makes use of the YAML anchor feature to avoid having to repeat the http section for multiple hosts that use the exact same paths. If this Ingress object will only be fronting one backend Service, we might instead create the following:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    external-dns.alpha.kubernetes.io/hostname: echoserver.mycluster.example.org, echoserver.example.org
    kubernetes.io/ingress.class: skipper
  name: echoserver
spec:
  rules:
  - http:
      paths:
      - backend:
          serviceName: echoserver
          servicePort: 80
        path: /

In the above example we create a default path that works for any hostname, and make use of the external-dns.alpha.kubernetes.io/hostname annotation to create multiple aliases for the resulting ALB.

Dualstack ALBs

AWS supports both IPv4 and "dualstack" (both IPv4 and IPv6) interfaces for ALBs. The Kubernetes Ingress AWS controller supports the alb.ingress.kubernetes.io/ip-address-type annotation (which defaults to ipv4) to determine this. If this annotation is set to dualstack then ExternalDNS will create two alias records (one A record and one AAAA record) for each hostname associated with the Ingress object.

Example:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    alb.ingress.kubernetes.io/ip-address-type: dualstack
    kubernetes.io/ingress.class: skipper
  name: echoserver
spec:
  rules:
  - host: echoserver.example.org
    http:
      paths:
      - backend:
          serviceName: echoserver
          servicePort: 80
        path: /

The above Ingress object will result in the creation of an ALB with a dualstack interface. ExternalDNS will create both an A echoserver.example.org record and an AAAA record of the same name, that each are aliases for the same ALB.

NLBs

AWS has NLBs and kube-ingress-aws-controller is able to create NLBs instead of ALBs. The Kubernetes Ingress AWS controller supports the zalando.org/aws-load-balancer-type annotation (which defaults to alb) to determine this. If this annotation is set to nlb then ExternalDNS will create an NLB instead of an ALB.

Example:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    zalando.org/aws-load-balancer-type: nlb
    kubernetes.io/ingress.class: skipper
  name: echoserver
spec:
  rules:
  - host: echoserver.example.org
    http:
      paths:
      - backend:
          serviceName: echoserver
          servicePort: 80
        path: /

The above Ingress object will result in the creation of an NLB. A successful create, you can observe in the ingress status field, that is written by kube-ingress-aws-controller:

status:
  loadBalancer:
    ingress:
    - hostname: kube-ing-lb-atedkrlml7iu-1681027139.$region.elb.amazonaws.com

ExternalDNS will create a A-records echoserver.example.org, that use AWS ALIAS record to automatically maintain IP addresses of the NLB.

RouteGroup (optional)

Kube-ingress-aws-controller, Skipper and external-dns support RouteGroups. External-dns needs to be started with --source=skipper-routegroup parameter in order to work on RouteGroup objects.

Here we can not show all RouteGroup capabilities, but we show one simple example with an application and a custom https redirect.

apiVersion: zalando.org/v1
kind: RouteGroup
metadata:
  name: my-route-group
spec:
  backends:
  - name: my-backend
    type: service
    serviceName: my-service
    servicePort: 80
  - name: redirectShunt
    type: shunt
  defaultBackends:
  - backendName: my-service
  routes:
  - pathSubtree: /
  - pathSubtree: /
    predicates:
    - Header("X-Forwarded-Proto", "http")
    filters:
    - redirectTo(302, "https:")
    backends:
    - redirectShunt