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:
- kube-ingress-aws-controller
- skipper
- external-dns
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:
name: echoserver
spec:
ingressClassName: skipper
rules:
- host: echoserver.mycluster.example.org
http: &echoserver_root
paths:
- path: /
backend:
service:
name: echoserver
port:
number: 80
pathType: Prefix
- 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
name: echoserver
spec:
ingressClassName: skipper
rules:
- http:
paths:
- path: /
backend:
service:
name: echoserver
port:
number: 80
pathType: Prefix
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
name: echoserver
spec:
ingressClassName: skipper
rules:
- host: echoserver.example.org
http:
paths:
- path: /
backend:
service:
name: echoserver
port:
number: 80
pathType: Prefix
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
name: echoserver
spec:
ingressClassName: skipper
rules:
- host: echoserver.example.org
http:
paths:
- path: /
backend:
service:
name: echoserver
port:
number: 80
pathType: Prefix
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