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ExternalDNS

ExternalDNS

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ExternalDNS synchronizes exposed Kubernetes Services and Ingresses with DNS providers.

What It Does

Inspired by Kubernetes DNS, Kubernetes’ cluster-internal DNS server, ExternalDNS makes Kubernetes resources discoverable via public DNS servers. Like KubeDNS, it retrieves a list of resources (Services, Ingresses, etc.) from the Kubernetes API to determine a desired list of DNS records. Unlike KubeDNS, however, it’s not a DNS server itself, but merely configures other DNS providers accordingly—e.g. AWS Route 53 or Google Cloud DNS.

In a broader sense, ExternalDNS allows you to control DNS records dynamically via Kubernetes resources in a DNS provider-agnostic way.

The FAQ contains additional information and addresses several questions about key concepts of ExternalDNS.

To see ExternalDNS in action, have a look at this video or read this blogpost.

The Latest Release

ExternalDNS allows you to keep selected zones (via --domain-filter) synchronized with Ingresses and Services of type=LoadBalancer and nodes in various DNS providers:
* Google Cloud DNS
* AWS Route 53
* AWS Cloud Map
* AzureDNS
* BlueCat
* Civo
* CloudFlare
* RcodeZero
* DigitalOcean
* DNSimple
* Infoblox
* Dyn
* OpenStack Designate
* PowerDNS
* CoreDNS
* Exoscale
* Oracle Cloud Infrastructure DNS
* Linode DNS
* RFC2136
* NS1
* TransIP
* VinylDNS
* Vultr
* OVH
* Scaleway
* Akamai Edge DNS
* GoDaddy
* Gandi
* ANS Group SafeDNS
* IBM Cloud DNS
* TencentCloud PrivateDNS
* TencentCloud DNSPod
* Plural
* Pi-hole

ExternalDNS is, by default, aware of the records it is managing, therefore it can safely manage non-empty hosted zones. We strongly encourage you to set --txt-owner-id to a unique value that doesn’t change for the lifetime of your cluster. You might also want to run ExternalDNS in a dry run mode (--dry-run flag) to see the changes to be submitted to your DNS Provider API.

Note that all flags can be replaced with environment variables; for instance,
--dry-run could be replaced with EXTERNAL_DNS_DRY_RUN=1.

Status of providers

ExternalDNS supports multiple DNS providers which have been implemented by the ExternalDNS contributors. Maintaining all of those in a central repository is a challenge and we have limited resources to test changes. This means that it is very hard to test all providers for possible regressions and, as written in the Contributing section, we encourage contributors to step in as maintainers for the individual providers and help by testing the integrations.

End-to-end testing of ExternalDNS is currently
performed
in the separate
kubernetes-on-aws
repository.

We define the following stability levels for providers:

  • Stable: Used for smoke tests before a release, used in production and maintainers are active.
  • Beta: Community supported, well tested, but maintainers have no access to resources to execute integration tests on the real platform and/or are not using it in production.
  • Alpha: Community provided with no support from the maintainers apart from reviewing PRs.

The following table clarifies the current status of the providers according to the aforementioned stability levels:

Provider Status Maintainers
Google Cloud DNS Stable
AWS Route 53 Stable
AWS Cloud Map Beta
Akamai Edge DNS Beta
AzureDNS Beta
BlueCat Alpha @seanmalloy @vinny-sabatini
Civo Alpha @alejandrojnm
CloudFlare Beta
RcodeZero Alpha
DigitalOcean Alpha
DNSimple Alpha
Infoblox Alpha @saileshgiri
Dyn Alpha
OpenStack Designate Alpha
PowerDNS Alpha
CoreDNS Alpha
Exoscale Alpha
Oracle Cloud Infrastructure DNS Alpha
Linode DNS Alpha
RFC2136 Alpha
NS1 Alpha
TransIP Alpha
VinylDNS Alpha
RancherDNS Alpha
OVH Alpha
Scaleway DNS Alpha @Sh4d1
Vultr Alpha
UltraDNS Alpha
GoDaddy Alpha
Gandi Alpha @packi
SafeDNS Alpha @assureddt
IBMCloud Alpha @hughhuangzh
TencentCloud Alpha @Hyzhou
Plural Alpha @michaeljguarino
Pi-hole Alpha @tinyzimmer

Kubernetes version compatibility

A breaking change was added in external-dns v0.10.0.

ExternalDNS <= 0.9.x >= 0.10.0
Kubernetes <= 1.18 ✅ ❌
Kubernetes >= 1.19 and <= 1.21 ✅ ✅
Kubernetes >= 1.22 ❌ ✅

Running ExternalDNS:

The are two ways of running ExternalDNS:

  • Deploying to a Cluster
  • Running Locally

Deploying to a Cluster

The following tutorials are provided:

Running Locally

See the contributor guide for details on compiling
from source.

Setup Steps

Next, run an application and expose it via a Kubernetes Service:

kubectl run nginx --image=nginx --port=80
kubectl expose pod nginx --port=80 --target-port=80 --type=LoadBalancer

Annotate the Service with your desired external DNS name. Make sure to change example.org to your domain.

kubectl annotate service nginx "external-dns.alpha.kubernetes.io/hostname=nginx.example.org."

Optionally, you can customize the TTL value of the resulting DNS record by using the external-dns.alpha.kubernetes.io/ttl annotation:

kubectl annotate service nginx "external-dns.alpha.kubernetes.io/ttl=10"

For more details on configuring TTL, see here.

Use the internal-hostname annotation to create DNS records with ClusterIP as the target.

kubectl annotate service nginx "external-dns.alpha.kubernetes.io/internal-hostname=nginx.internal.example.org."

If the service is not of type Loadbalancer you need the –publish-internal-services flag.

Locally run a single sync loop of ExternalDNS.

external-dns --txt-owner-id my-cluster-id --provider google --google-project example-project --source service --once --dry-run

This should output the DNS records it will modify to match the managed zone with the DNS records you desire. It also assumes you are running in the default namespace. See the FAQ for more information regarding namespaces.

Note: TXT records will have the my-cluster-id value embedded. Those are used to ensure that ExternalDNS is aware of the records it manages.

Once you’re satisfied with the result, you can run ExternalDNS like you would run it in your cluster: as a control loop, and not in dry-run mode:

external-dns --txt-owner-id my-cluster-id --provider google --google-project example-project --source service

Check that ExternalDNS has created the desired DNS record for your Service and that it points to its load balancer’s IP. Then try to resolve it:

dig +short nginx.example.org.
104.155.60.49

Now you can experiment and watch how ExternalDNS makes sure that your DNS records are configured as desired. Here are a couple of things you can try out:
* Change the desired hostname by modifying the Service’s annotation.
* Recreate the Service and see that the DNS record will be updated to point to the new load balancer IP.
* Add another Service to create more DNS records.
* Remove Services to clean up your managed zone.

The tutorials section contains examples, including Ingress resources, and shows you how to set up ExternalDNS in different environments such as other cloud providers and alternative Ingress controllers.

Note

If using a txt registry and attempting to use a CNAME the --txt-prefix must be set to avoid conflicts. Changing --txt-prefix will result in lost ownership over previously created records.

If externalIPs list is defined for a LoadBalancer service, this list will be used instead of an assigned load balancer IP to create a DNS record. It’s useful when you run bare metal Kubernetes clusters behind NAT or in a similar setup, where a load balancer IP differs from a public IP (e.g. with MetalLB).

Contributing

Are you interested in contributing to external-dns? We, the maintainers and community, would love your
suggestions, contributions, and help! Also, the maintainers can be contacted at any time to learn more
about how to get involved.

We also encourage ALL active community participants to act as if they are maintainers, even if you don’t have
“official” write permissions. This is a community effort, we are here to serve the Kubernetes community. If you
have an active interest and you want to get involved, you have real power! Don’t assume that the only people who
can get things done around here are the “maintainers”. We also would love to add more “official” maintainers, so
show us what you can do!

The external-dns project is currently in need of maintainers for specific DNS providers. Ideally each provider
would have at least two maintainers. It would be nice if the maintainers run the provider in production, but it
is not strictly required. Provider listed here
that do not have a maintainer listed are in need of assistance.

Read the contributing guidelines and have a look at the contributing docs to learn about building the project, the project structure, and the purpose of each package.

For an overview on how to write new Sources and Providers check out Sources and Providers.

Heritage

ExternalDNS is an effort to unify the following similar projects in order to bring the Kubernetes community an easy and predictable way of managing DNS records across cloud providers based on their Kubernetes resources:

User Demo How-To Blogs and Examples

Last update: August 4, 2023
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