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Frequently asked questions

How is ExternalDNS useful to me?

You've probably created many deployments. Typically, you expose your deployment to the Internet by creating a Service with type=LoadBalancer. Depending on your environment, this usually assigns a random publicly available endpoint to your service that you can access from anywhere in the world. On Google Container Engine, this is a public IP address:

$ kubectl get svc
NAME      CLUSTER-IP     EXTERNAL-IP     PORT(S)        AGE
nginx     10.3.249.226   35.187.104.85   80:32281/TCP   1m

But dealing with IPs for service discovery isn't nice, so you register this IP with your DNS provider under a better name—most likely, one that corresponds to your service name. If the IP changes, you update the DNS record accordingly.

Those times are over! ExternalDNS takes care of that last step for you by keeping your DNS records synchronized with your external entry points.

ExternalDNS' usefulness also becomes clear when you use Ingresses to allow external traffic into your cluster. Via Ingress, you can tell Kubernetes to route traffic to different services based on certain HTTP request attributes, e.g. the Host header:

$ kubectl get ing
NAME         HOSTS                                      ADDRESS         PORTS     AGE
entrypoint   frontend.example.org,backend.example.org   35.186.250.78   80        1m

But there's nothing that actually makes clients resolve those hostnames to the Ingress' IP address. Again, you normally have to register each entry with your DNS provider. Only if you're lucky can you use a wildcard, like in the example above.

ExternalDNS can solve this for you as well.

Which DNS providers are supported?

Currently, the following providers are supported:

  • Google CloudDNS
  • AWS Route 53
  • AzureDNS
  • CloudFlare
  • DigitalOcean
  • DNSimple
  • Infoblox
  • Dyn
  • OpenStack Designate
  • PowerDNS
  • CoreDNS
  • Exoscale
  • Oracle Cloud Infrastructure DNS
  • Linode DNS
  • RFC2136

As stated in the README, we are currently looking for stable maintainers for those providers, to ensure that bugfixes and new features will be available for all of those.

Which Kubernetes objects are supported?

Services exposed via type=LoadBalancer and for the hostnames defined in Ingress objects as well as headless hostPort services. An initial effort to support type NodePort was started as of May 2018 and it is in progress at the time of writing.

How do I specify a DNS name for my Kubernetes objects?

There are three sources of information for ExternalDNS to decide on DNS name. ExternalDNS will pick one in order as listed below:

  1. For ingress objects ExternalDNS will create a DNS record based on the host specified for the ingress object. For services ExternalDNS will look for the annotation external-dns.alpha.kubernetes.io/hostname on the service and use the corresponding value.

  2. If compatibility mode is enabled (e.g. --compatibility={mate,molecule} flag), External DNS will parse annotations used by Zalando/Mate, wearemolecule/route53-kubernetes. Compatibility mode with Kops DNS Controller is planned to be added in the future.

  3. If --fqdn-template flag is specified, e.g. --fqdn-template={{.Name}}.my-org.com, ExternalDNS will use service/ingress specifications for the provided template to generate DNS name.

Can I specify multiple global FQDN templates?

Yes, you can. Pass in a comma separated list to --fqdn-template. Beaware this will double (triple, etc) the amount of DNS entries based on how many services, ingresses and so on you have and will get you faster towards the API request limit of your DNS provider.

Which Service and Ingress controllers are supported?

Regarding Services, we'll support the OSI Layer 4 load balancers that Kubernetes creates on AWS and Google Container Engine, and possibly other clusters running on Google Compute Engine.

Regarding Ingress, we'll support:

Are other Ingress Controllers supported?

For Ingress objects, ExternalDNS will attempt to discover the target hostname of the relevant Ingress Controller automatically. If you are using an Ingress Controller that is not listed above you may have issues with ExternalDNS not discovering Endpoints and consequently not creating any DNS records. As a workaround, it is possible to force create an Endpoint by manually specifying a target host/IP for the records to be created by setting the annotation external-dns.alpha.kubernetes.io/target in the Ingress object.

Another reason you may want to override the ingress hostname or IP address is if you have an external mechanism for handling failover across ingress endpoints. Possible scenarios for this would include using keepalived-vip to manage failover faster than DNS TTLs might expire.

Note that if you set the target to a hostname, then a CNAME record will be created. In this case, the hostname specified in the Ingress object's annotation must already exist. (i.e. you have a Service resource for your Ingress Controller with the external-dns.alpha.kubernetes.io/hostname annotation set to the same value.)

What about other projects similar to ExternalDNS?

ExternalDNS is a joint effort to unify different projects accomplishing the same goals, namely:

We strive to make the migration from these implementations a smooth experience. This means that, for some time, we'll support their annotation semantics in ExternalDNS and allow both implementations to run side-by-side. This enables you to migrate incrementally and slowly phase out the other implementation.

How does it work with other implementations and legacy records?

ExternalDNS will allow you to opt into any Services and Ingresses that you want it to consider, by an annotation. This way, it can co-exist with other implementations running in the same cluster if they also support this pattern. However, we'll most likely declare ExternalDNS to be the default implementation. This means that ExternalDNS will consider Services and Ingresses that don't specifically declare which controller they want to be processed by; this is similar to the ingress.class annotation on GKE.

I'm afraid you will mess up my DNS records!

ExternalDNS since v0.3 implements the concept of owning DNS records. This means that ExternalDNS will keep track of which records it has control over, and will never modify any records over which it doesn't have control. This is a fundamental requirement to operate ExternalDNS safely when there might be other actors creating DNS records in the same target space.

For now ExternalDNS uses TXT records to label owned records, and there might be other alternatives coming in the future releases.

Does anyone use ExternalDNS in production?

Yes, multiple companies are using ExternalDNS in production. Zalando, as an example, has been using it in production since its v0.3 release, mostly using the AWS provider.

How can we start using ExternalDNS?

Check out the following descriptive tutorials on how to run ExternalDNS in GKE and AWS or any other supported provider.

Why is ExternalDNS only adding a single IP address in Route 53 on AWS when using the nginx-ingress-controller? How do I get it to use the FQDN of the ELB assigned to my nginx-ingress-controller Service instead?

By default the nginx-ingress-controller assigns a single IP address to an Ingress resource when it's created. ExternalDNS uses what's assigned to the Ingress resource, so it too will use this single IP address when adding the record in Route 53.

In most AWS deployments, you'll instead want the Route 53 entry to be the FQDN of the ELB that is assigned to the nginx-ingress-controller Service. To accomplish this, when you create the nginx-ingress-controller Deployment, you need to provide the --publish-service option to the /nginx-ingress-controller executable under args. Once this is deployed new Ingress resources will get the ELB's FQDN and ExternalDNS will use the same when creating records in Route 53.

According to the nginx-ingress-controller docs the value you need to provide --publish-service is:

Service fronting the ingress controllers. Takes the form namespace/name. The controller will set the endpoint records on the ingress objects to reflect those on the service.

For example if your nginx-ingress-controller Service's name is nginx-ingress-controller-svc and it's in the default namespace the start of your resource YAML might look like the following. Note the second to last line.

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-ingress-controller
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx-ingress
    spec:
      hostNetwork: false
      containers:
        - name: nginx-ingress-controller
          image: "gcr.io/google_containers/nginx-ingress-controller:0.9.0-beta.11"
          imagePullPolicy: "IfNotPresent"
          args:
            - /nginx-ingress-controller
            - --default-backend-service={your-backend-service}
            - --publish-service=default/nginx-ingress-controller-svc
            - --configmap={your-configmap}

I have a Service/Ingress but it's ignored by ExternalDNS. Why?

ExternalDNS can be configured to only use Services or Ingresses as source. In case Services or Ingresses seem to be ignored in your setup, consider checking how the flag --source was configured when deployed. For reference, see the issue kubernetes-sigs#267.

I'm using an ELB with TXT registry but the CNAME record clashes with the TXT record. How to avoid this?

CNAMEs cannot co-exist with other records, therefore you can use the --txt-prefix flag which makes sure to create a TXT record with a name following the pattern prefix.<CNAME record>. For reference, see the issue kubernetes-sigs#262.

Which permissions do I need when running ExternalDNS on a GCE or GKE node.

You need to add either https://www.googleapis.com/auth/ndev.clouddns.readwrite or https://www.googleapis.com/auth/cloud-platform on your instance group's scope.

How can I run ExternalDNS under a specific GCP Service Account, e.g. to access DNS records in other projects?

Have a look at https://github.com/linki/mate/blob/v0.6.2/examples/google/README.md#permissions

How do I configure multiple Sources via environment variables? (also applies to domain filters)

Separate the individual values via a line break. The equivalent of --source=service --source=ingress would be service\ningress. However, it can be tricky do define that depending on your environment. The following examples work (zsh):

Via docker:

$ docker run \
  -e EXTERNAL_DNS_SOURCE=$'service\ningress' \
  -e EXTERNAL_DNS_PROVIDER=google \
  -e EXTERNAL_DNS_DOMAIN_FILTER=$'foo.com\nbar.com' \
  registry.opensource.zalan.do/teapot/external-dns:latest
time="2017-08-08T14:10:26Z" level=info msg="config: &{Master: KubeConfig: Sources:[service ingress] Namespace: ...

Locally:

$ export EXTERNAL_DNS_SOURCE=$'service\ningress'
$ external-dns --provider=google
INFO[0000] config: &{Master: KubeConfig: Sources:[service ingress] Namespace: ...
$ EXTERNAL_DNS_SOURCE=$'service\ningress' external-dns --provider=google
INFO[0000] config: &{Master: KubeConfig: Sources:[service ingress] Namespace: ...

In a Kubernetes manifest:

spec:
  containers:
  - name: external-dns
    args:
    - --provider=google
    env:
    - name: EXTERNAL_DNS_SOURCE
      value: "service\ningress"

Or preferably:

spec:
  containers:
  - name: external-dns
    args:
    - --provider=google
    env:
    - name: EXTERNAL_DNS_SOURCE
      value: |-
        service
        ingress

Running an internal and external dns service

Sometimes you need to run an internal and an external dns service. The internal one should provision hostnames used on the internal network (perhaps inside a VPC), and the external one to expose DNS to the internet.

To do this with ExternalDNS you can use the --annotation-filter to specifically tie an instance of ExternalDNS to an instance of a ingress controller. Let's assume you have two ingress controllers nginx-internal and nginx-external then you can start two ExternalDNS providers one with --annotation-filter=kubernetes.io/ingress.class=nginx-internal and one with --annotation-filter=kubernetes.io/ingress.class=nginx-external.