Developer Reference

The external-dns is the work of thousands of contributors, and is maintained by a small team within kubernetes-sigs. This document covers basic needs to work with external-dns codebase. It contains instructions to build, run, and test external-dns.

Tools

Building and/or testing external-dns requires additional tooling.

• Git
• Go 1.25+
• Go modules
• golangci-lint
• ko
• kubectl
• helm
• spectral
• python

Go Tools

Additional Go-based tools are managed in go.tool.mod and used for code generation:

Tool	Purpose
controller-gen	Generates CRD manifests and deepcopy methods
yq	YAML processing (splitting, filtering CRD outputs)
yamlfmt	YAML formatting

List all installed Go tools:

make go-tools

Update Go tools to their latest versions:

make update-tools-deps

Note: Updates are done manually because Dependabot does not yet support go.tool.mod
(dependabot-core#12050).

First Steps

Configure Development Environment

You must have a working Go environment, compile the build, and set up testing.

git clone https://github.com/kubernetes-sigs/external-dns.git && cd external-dns

Building & Testing

The project uses the make build system. It’ll run code generators, tests and static code analysis.

Build, run tests and lint the code:

make go-lint
make test
make cover-html

If added any flags or metrics, re-generate documentation

make generate-flags-documentation
make generate-metrics-documentation

We require all changes to be covered by acceptance tests and/or unit tests, depending on the situation.
In the context of the external-dns, acceptance tests are tests of interactions with providers, such as creating, reading information about, and destroying DNS resources. In contrast, unit tests test functionality wholly within the codebase itself, such as function tests.

Log Unit Testing

Testing log messages within codebase provides significant advantages, especially when it comes to debugging, monitoring, and gaining a deeper understanding of system behavior. Log library build-in testing functionality

This practice enables:

• Early detection of logging issues
• Verification of Important Information
• Ensuring Correct Severity Levels
• Improving Observability and Monitoring
• Driving Better Logging Practices

To illustrate how to unit test log output within functions, consider the following example:

import (
    "testing"

    "sigs.k8s.io/external-dns/internal/testutils"
)

func TestMe(t *testing.T) {
  hook := testutils.LogsUnderTestWithLogLevel(log.WarnLevel, t)
  ... function under tests ...
  testutils.TestHelperLogContains("example warning message", hook, t)
  // provide negative assertion
  testutils.TestHelperLogNotContains("this message should not be shown", hook, t)
}

CRD Generation

The DNSEndpoint CRD manifest is generated from Go types using controller-gen and must be regenerated whenever the types in endpoint/ or apis/ change.

make crd

This runs scripts/generate-crd.sh which:

1. Generates DeepCopy methods for types in endpoint/ and apis/
2. Generates the CRD manifest into config/crd/standard/
3. Copies the CRD (with filtered annotations) into charts/external-dns/crds/

The controller-gen.kubebuilder.io/version annotation in the generated YAML reflects the version of controller-gen from go.tool.mod at generation time and is updated automatically.

Integration Tests

Integration tests live in tests/integration/ and verify behavior that spans multiple sources or wrappers together, using a fake Kubernetes client — no real cluster is required.

Where integration tests sit

flowchart TD
    E2E["E2E Tests<br>Real cluster + real DNS provider<br>Slow · requires cloud credentials"]
    IT["Integration Tests  ←  tests/integration/<br>Fake Kubernetes API · no cluster needed<br>Tests source + wrapper combinations · fast<br>Declarative YAML scenarios"]
    UT["Unit Tests<br>One source or wrapper in isolation<br>Mocked or minimal Kubernetes client"]

    E2E --> IT --> UT

    style IT fill:#bbf7d0,stroke:#15803d,stroke-width:2px

What runs during a test

flowchart LR
    subgraph yaml["tests/integration/scenarios/tests.yaml"]
        RES["resources<br>Service · Ingress · Pod"]
        CFG["config<br>sources · filters · wrappers"]
        EXP["expected<br>endpoints"]
    end

    subgraph toolkit["toolkit  —  fake Kubernetes"]
        PARSE["ParseResources()"]
        FAKE["fake.Clientset"]
        WRAP["CreateWrappedSource()"]
    end

    subgraph pipeline["ExternalDNS pipeline under test"]
        SRC["Source(s)<br>service · ingress · ..."]
        WRP["Wrapper(s)<br>dedup · targetFilter · NAT64"]
        OUT["Endpoints"]
    end

    ASSERT["ValidateEndpoints()<br>DNSName · Targets<br>RecordType · TTL"]

    RES --> PARSE --> FAKE --> WRAP
    CFG --> WRAP
    WRAP --> SRC --> WRP --> OUT --> ASSERT
    EXP --> ASSERT

When to add an integration test:

• You are adding or changing a source (e.g. service, ingress) and want to verify it produces the correct endpoints end-to-end.
• You are changing a wrapper (e.g. deduplication, target filtering, default targets, NAT64) and want to verify it behaves correctly when real Kubernetes resources are involved.
• You are changing a post-processor and want to confirm it applies correctly to endpoints produced by one or more sources.
• You are verifying multiple sources together (e.g. service and ingress both pointing to the same hostname) and their combined output.
• You are fixing a cross-cutting bug that only manifests when sources, wrappers, and post-processors interact.
• A unit test would require mocking too many internals — an integration test can express the scenario more clearly as a real Kubernetes resource.

How to add a scenario:

Add an entry to tests/integration/scenarios/tests.yaml. Each scenario declares Kubernetes resources (Service, Ingress, etc.), the ExternalDNS source configuration, and the expected endpoints:

- name: my-new-scenario
  description: >
    Brief explanation of what behavior this scenario validates.
  config:
    sources: ["service"]
  resources:
    - resource:
        apiVersion: v1
        kind: Service
        metadata:
          name: my-svc
          namespace: default
          annotations:
            external-dns.alpha.kubernetes.io/hostname: my.example.com
        spec:
          type: LoadBalancer
        status:
          loadBalancer:
            ingress:
              - ip: 1.2.3.4
  expected:
    - dnsName: my.example.com
      targets: ["1.2.3.4"]
      recordType: A

How to run:

go test ./tests/integration/...

Complete test on local env

It’s possible to run ExternalDNS locally. CoreDNS can be used for easier testing.
See the related tutorials for full instructions.

Continuous Integration

When submitting a pull request, you’ll notice that we run several automated processes on your proposed change. Some of these processes are tests to ensure your contribution aligns with our standards. While we strive for accuracy, some users may find these tests confusing.

Execute code without building binary

The external-dns does not require make build. You could compile and run Go program with the command

go run main.go \
    --provider=aws \
    --registry=txt \
    --source=fake \
    --log-level=info

For this command to run successfully, it will require AWS credentials and access to local or remote access.

To run local cluster please refer to running local cluster

Deploying a local build

After building local images, it is often useful to deploy those images in a local cluster

We use Minikube but it could be Kind or any other solution.

• Create local cluster
• Build and load local images
• Deploy with Helm
• Deploy with kubernetes manifests

Create a local cluster

For simplicity, minikube can be used to create a single
node cluster.

You can set a specific Kubernetes version by setting the node’s container image.
See basic controls within the documentation about configuration for more details on this.

Once you have a configuration in place, create the cluster with
that configuration:

minikube start \
  --profile=external-dns \
  --memory=2000 \
  --cpus=2 \
  --disk-size=5g \
  --kubernetes-version=v1.31 \
  --driver=docker

minikube profile external-dns

After the new Kubernetes cluster is ready, identify the cluster is running as the single node cluster:

❯❯ kubectl get nodes
NAME           STATUS   ROLES           AGE   VERSION
external-dns   Ready    control-plane   16s   v1.31.4

---

Building local images

When building local images with ko you can’t specify the registry used to create the image names. It will always be ko.local.

• minikube handbooks

Note: You could skip this step if you build and push image to your private registry or using an official external-dns image

❯❯ export KO_DOCKER_REPO=ko.local
❯❯ export VERSION=v1
❯❯ docker context use rancher-desktop ## (optional) this command is only required when using rancher-desktop
❯❯ ls -al /var/run/docker.sock ## (optional) validate that docker runtime is configured correctly and symlink exists

❯❯ ko build --tags ${VERSION}
❯❯ docker images
$$ ko.local/external-dns-9036f6870f30cbdefa42a10f30bada63   local-v1

Push image to minikube

Refer to load image

❯❯ minikube image load ko.local/external-dns-9036f6870f30cbdefa42a10f30bada63:local-v1
❯❯ minikube image ls
$$ registry.k8s.io/pause:3.10
$$ ...
$$ ko.local/external-dns-9036f6870f30cbdefa42a10f30bada63:local-v1
$$ ...
❯❯ kubectl run external-dns --image=ko.local/external-dns-9036f6870f30cbdefa42a10f30bada63:local-v1 --image-pull-policy=Never

Build and push directly in minikube

Any docker command you run in this current terminal will run against the docker inside minikube cluster.

Refer to push directly

❯❯ eval $(minikube -p external-dns docker-env)
❯❯ echo $MINIKUBE_ACTIVE_DOCKERD
$$ external-dns
❯❯ export VERSION=v1
❯❯ ko build --local --tags ${VERSION}
❯❯ docker images
$$ REPOSITORY                                               TAG
$$ registry.k8s.io/kube-apiserver                           v1.31.4
$$ ....
$$ ko.local/external-dns-9036f6870f30cbdefa42a10f30bada63   minikube-v1
$$ ...
❯❯ eval $(minikube docker-env -u) ## unset minikube

Pushing to an in-cluster using Registry addon

Refer to pushing images for a full configuration

❯❯ export KO_DOCKER_REPO=$(minikube ip):5000
❯❯ export VERSION=registry-v1
❯❯ minikube addons enable registry
❯❯ ko build --tags ${VERSION}

Building image and push to a registry

Build container image and push to a specific registry

make build.push IMAGE=your-registry/external-dns

---

Deploy with Helm

Build local images if required, load them on a local cluster, and deploy helm charts, run:

Render chart templates locally and display the output

❯❯ helm lint --debug charts/external-dns
❯❯ helm template external-dns charts/external-dns --output-dir _scratch

Deploy manifests to a cluster with required values

❯❯ kubectl apply -f _scratch --recursive=true

Modify chart or values and validate the diff

❯❯ helm template external-dns charts/external-dns --output-dir _scratch
❯❯ kubectl diff -f _scratch/external-dns --recursive=true --show-managed-fields=false

Helm Values

This helm chart comes with a JSON schema generated from values with helm schema plugin.

1. Install required plugin(s)

❯❯ scripts/helm-tools.sh --install

1. Ensure that the schema is always up-to-date

❯❯ scripts/helm-tools.sh --diff

1. When not up-to-date, update JSON schema

❯❯ scripts/helm-tools.sh --schema

1. Runs a series of tests to verify that the chart is well-formed, linted and JSON schema is valid

❯❯ scripts/helm-tools.sh --lint

1. Auto-generate documentation for helm charts into markdown files.

❯❯ scripts/helm-tools.sh --docs

1. Run helm unittests.

❯❯ make helm-test

1. Add an entry to the chart CHANGELOG.md under ## UNRELEASED section and open pull request

Deploy with kubernetes manifests

Note; kubernetes manifest are not up to date. Consider to create an examples folder

kubectl apply -f kustomize --recursive=true --dry-run=client

Contribute to documentation

All documentation is in docs folder. If new page is added or removed, make sure mkdocs.yml is also updated.

Install required dependencies. In order to not to break system packages, we are going to use virtual environments with pipenv.

❯❯ pipenv shell
❯❯ pip install -r docs/scripts/requirements.txt
❯❯ mkdocs serve
$$ ...
$$ Serving on http://127.0.0.1:8000/

How to add an example snippet

Let’s say we are improving tutorial location in docs/tutorials/aws.md.

1. Add a snippet to docs/snippets/aws/<snippet-name>.<snippet-extension>
2. Add snippet to a markdown file docs/tutorials/aws.md

  ```extension
    [[% include 'snippets/aws/<snippet-name>.<snippet-extension>' %]]
  ```