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Configuring ExternalDNS to use the Istio Gateway and/or Istio Virtual Service Source

This tutorial describes how to configure ExternalDNS to use the Istio Gateway source.
It is meant to supplement the other provider-specific setup tutorials.

Note: Using the Istio Gateway source requires Istio >=1.0.0.

  • Manifest (for clusters without RBAC enabled)
  • Manifest (for clusters with RBAC enabled)
  • Update existing ExternalDNS Deployment

Manifest (for clusters without RBAC enabled)

apiVersion: apps/v1
kind: Deployment
metadata:
  name: external-dns
spec:
  strategy:
    type: Recreate
  selector:
    matchLabels:
      app: external-dns
  template:
    metadata:
      labels:
        app: external-dns
    spec:
      containers:
      - name: external-dns
        image: k8s.gcr.io/external-dns/external-dns:v0.7.6
        args:
        - --source=service
        - --source=ingress
        - --source=istio-gateway        # choose one
        - --source=istio-virtualservice # or both
        - --domain-filter=external-dns-test.my-org.com # will make ExternalDNS see only the hosted zones matching provided domain, omit to process all available hosted zones
        - --provider=aws
        - --policy=upsert-only # would prevent ExternalDNS from deleting any records, omit to enable full synchronization
        - --aws-zone-type=public # only look at public hosted zones (valid values are public, private or no value for both)
        - --registry=txt
        - --txt-owner-id=my-identifier

Manifest (for clusters with RBAC enabled)

apiVersion: v1
kind: ServiceAccount
metadata:
  name: external-dns
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: external-dns
rules:
- apiGroups: [""]
  resources: ["services","endpoints","pods"]
  verbs: ["get","watch","list"]
- apiGroups: ["extensions","networking.k8s.io"]
  resources: ["ingresses"] 
  verbs: ["get","watch","list"]
- apiGroups: [""]
  resources: ["nodes"]
  verbs: ["list"]
- apiGroups: ["networking.istio.io"]
  resources: ["gateways", "virtualservices"]
  verbs: ["get","watch","list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: external-dns-viewer
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: external-dns
subjects:
- kind: ServiceAccount
  name: external-dns
  namespace: default
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: external-dns
spec:
  strategy:
    type: Recreate
  selector:
    matchLabels:
      app: external-dns
  template:
    metadata:
      labels:
        app: external-dns
    spec:
      serviceAccountName: external-dns
      containers:
      - name: external-dns
        image: k8s.gcr.io/external-dns/external-dns:v0.7.6
        args:
        - --source=service
        - --source=ingress
        - --source=istio-gateway
        - --source=istio-virtualservice
        - --domain-filter=external-dns-test.my-org.com # will make ExternalDNS see only the hosted zones matching provided domain, omit to process all available hosted zones
        - --provider=aws
        - --policy=upsert-only # would prevent ExternalDNS from deleting any records, omit to enable full synchronization
        - --aws-zone-type=public # only look at public hosted zones (valid values are public, private or no value for both)
        - --registry=txt
        - --txt-owner-id=my-identifier

Update existing ExternalDNS Deployment

  • For clusters with running external-dns, you can just update the deployment.
  • With access to the kube-system namespace, update the existing external-dns deployment.
  • Add a parameter to the arguments of the container to create dns entries with --source=istio-gateway.

Execute the following command or update the argument.

kubectl patch deployment external-dns --type='json' \
  -p='[{"op": "add", "path": "/spec/template/spec/containers/0/args/2", "value": "--source=istio-gateway" }]'

In case the setup uses a clusterrole, just append a new value to the enable the istio group.

kubectl patch clusterrole external-dns --type='json' \
  -p='[{"op": "add", "path": "/rules/4", "value": { "apiGroups": [ "networking.istio.io"], "resources": ["gateways"],"verbs": ["get", "watch", "list" ]} }]'

Verify that Istio Gateway/VirtualService Source works

Follow the Istio ingress traffic tutorial
to deploy a sample service that will be exposed outside of the service mesh.
The following are relevant snippets from that tutorial.

Install a sample service

With automatic sidecar injection:

$ kubectl apply -f https://raw.githubusercontent.com/istio/istio/release-1.6/samples/httpbin/httpbin.yaml

Otherwise:

$ kubectl apply -f <(istioctl kube-inject -f https://raw.githubusercontent.com/istio/istio/release-1.6/samples/httpbin/httpbin.yaml)

Using a Gateway as a source

Create an Istio Gateway:
$ cat <<EOF | kubectl apply -f -
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: httpbin-gateway
  namespace: istio-system
spec:
  selector:
    istio: ingressgateway # use Istio default gateway implementation
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "httpbin.example.com" # this is used by external-dns to extract DNS names
EOF
Configure routes for traffic entering via the Gateway:
$ cat <<EOF | kubectl apply -f -
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
spec:
  hosts:
  - "httpbin.example.com"
  gateways:
  - istio-system/httpbin-gateway
  http:
  - match:
    - uri:
        prefix: /status
    - uri:
        prefix: /delay
    route:
    - destination:
        port:
          number: 8000
        host: httpbin
EOF

Using a VirtualService as a source

Create an Istio Gateway:
$ cat <<EOF | kubectl apply -f -
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: httpbin-gateway
  namespace: istio-system
spec:
  selector:
    istio: ingressgateway # use Istio default gateway implementation
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "*"
EOF
Configure routes for traffic entering via the Gateway:
$ cat <<EOF | kubectl apply -f -
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
spec:
  hosts:
  - "httpbin.example.com" # this is used by external-dns to extract DNS names
  gateways:
  - istio-system/httpbin-gateway
  http:
  - match:
    - uri:
        prefix: /status
    - uri:
        prefix: /delay
    route:
    - destination:
        port:
          number: 8000
        host: httpbin
EOF

Access the sample service using curl

$ curl -I http://httpbin.example.com/status/200
HTTP/1.1 200 OK
server: envoy
date: Tue, 28 Aug 2018 15:26:47 GMT
content-type: text/html; charset=utf-8
access-control-allow-origin: *
access-control-allow-credentials: true
content-length: 0
x-envoy-upstream-service-time: 5

Accessing any other URL that has not been explicitly exposed should return an HTTP 404 error:

$ curl -I http://httpbin.example.com/headers
HTTP/1.1 404 Not Found
date: Tue, 28 Aug 2018 15:27:48 GMT
server: envoy
transfer-encoding: chunked

Note: The -H flag in the original Istio tutorial is no longer necessary in the curl commands.

Debug ExternalDNS

  • Look for the deployment pod to see the status

```console$ kubectl get pods | grep external-dns
external-dns-6b84999479-4knv9 1/1 Running 0 3h29m

* Watch for the logs as follows

```console
$ kubectl logs -f external-dns-6b84999479-4knv9

At this point, you can create or update any Istio Gateway object with hosts entries array.

ATTENTION: Make sure to specify those whose account is related to the DNS record.

  • Successful executions will print the following
time="2020-01-17T06:08:08Z" level=info msg="Desired change: CREATE httpbin.example.com A"
time="2020-01-17T06:08:08Z" level=info msg="Desired change: CREATE httpbin.example.com TXT"
time="2020-01-17T06:08:08Z" level=info msg="2 record(s) in zone example.com. were successfully updated"
time="2020-01-17T06:09:08Z" level=info msg="All records are already up to date, there are no changes for the matching hosted zones"
  • If there’s any problem around clusterrole, you would see the errors showing wrong permissions:
source \"gateways\" in API group \"networking.istio.io\" at the cluster scope"
time="2020-01-17T06:07:08Z" level=error msg="gateways.networking.istio.io is forbidden: User \"system:serviceaccount:kube-system:external-dns\" cannot list resource \"gateways\" in API group \"networking.istio.io\" at the cluster scope"
Last update: February 5, 2021
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