ExternalDNS accepts and consumes empty hostnames from annotation values

[seh]

What happened:

Create more than one Kubernetes Service and annotate it with "external-dns.alpha.kubernetes.io/hostname" with an empty string as the value. ExternalDNS will create a Route 53 change batch with two or more entries for the same empty hostname value.

What you expected to happen:

Ideally there would be two defenses against this problem:

• ExternalDNS should filter empty hostname values like this, treating the annotated Service or Ingress as an invalid candidate.
  Instead, it parses the annotation value as containing a single empty hostname, and proceeds to use it.
• ExternalDNS should not proceed as far as creating a Route 53 change batch with duplicate entries.

How to reproduce it (as minimally and precisely as possible):

• Use an image fresh enough to include Headless service: allow to specify target as NodeExternalIP or by annotation #2115 to test the headless Service scenario.
• Create two headless Services.
• Annotate each as follows:
  • external-dns.alpha.kubernetes.io/endpoints-type: "NodeExternalIP"
  • external-dns.alpha.kubernetes.io/hostname: "" (empty)
• Inspect ExternalDNS's log file.
• Note rejections from the AWS Route 53 API including the following text:

  "InvalidChangeBatch: [Duplicate Resource Record"

Anything else we need to know?:

I am not sure that the use of a headless Service and the use of the ".../endpoints-type" annotation is essential to reproducing the problem, but that describes the circumstances we found ourselves in. This is a configuration mistake in our Kubernetes manifests, but figuring out why ExternalDNS was consuming the annotations and reacting as it did was difficult.

Environment:

• External-DNS version (use external-dns --version): v0.11.0
• DNS provider: AWS Route 53

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/lifecycle stale

[seh]

/remove-lifecycle stale

This problem persists, and the fix is easy.

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/lifecycle stale

[seh]

/remove-lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough contributors to adequately respond to all issues and PRs.

This bot triages issues and PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
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/lifecycle stale

[seh]

/remove-lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough contributors to adequately respond to all issues.

This bot triages un-triaged issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
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/lifecycle stale

[seh]

/remove-lifecycle stale

[k8s-triage-robot]

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This bot triages un-triaged issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
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/lifecycle stale

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/lifecycle rotten

[k8s-triage-robot]

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• After 90d of inactivity, lifecycle/stale is applied
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/close not-planned

[k8s-ci-robot]

@k8s-triage-robot: Closing this issue, marking it as "Not Planned".

In response to this:

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues and PRs.

This bot triages issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
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You can:

• Reopen this issue with /reopen
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Please send feedback to sig-contributor-experience at kubernetes/community.

/close not-planned

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