fix(registry): handle empty targets in TXT records logging an error

[saikatharryc]

Description

Fixes #5129

Context: TXT record with routing policy on GCP has no direct single target, as a result, the direct index access to first element fails. (Such routing policy based records not necessarily be part of the external dns management area, it could be created or updated manually that can cause this issue.)

How to test manually:
Let the external-dns run as is , the google DNS zone you are using , create a TXT record with weighted routing policy.
Current version should crash with the error in the issue.
in the PR changes will make sure it gets passed by, with a error line like below

ERRO[0002] TXT record <DNS> has no targets

Checklist

• Unit tests updated
• End user documentation updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: saikatharryc / name: Saikat Chakrabortty (2e0c62a, 4ef055b, d097f9c, b0198c8)

[k8s-ci-robot]

Hi @saikatharryc. Thanks for your PR.

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[saikatharryc]

/check-cla

[ivankatliarchuk]

Hi, could you provide actual CLI commands and kubernetes manifets so I could validate this?

/ok-to-test

[saikatharryc]

Hi, could you provide actual CLI commands and kubernetes manifets so I could validate this?

/ok-to-test

Running this in any situation and creating a google DNS weighted TXT record should do it.
i built it and ran it locally connecting to a running GKE cluster

make build
./build/external-dns --dry-run \
--log-level=debug \
--log-format=text \
--domain-filter=xxx.io \
--domain-filter=xxx.io \
--domain-filter=xxx.io \
--domain-filter=xxx.io \
--policy=sync \
--provider=google \
--registry=txt \
--interval=1m \
--source=service \
--source=ingress \
--google-project=xxx-devops-tests \
--google-batch-change-size=1000

[ivankatliarchuk]

Could you share a kubernetes manifest that is breaking things?

[saikatharryc]

Could you share a kubernetes manifest that is breaking things?

This is not dependent or triggered from resources within the kubernetes, but weighted TXT records created/converted(manually) within the GCP dns zone, causing the external DNS not able to parse and crash.

[ivankatliarchuk]

is this an example record that acts as poison pill?

test.dev-apps-gcloud-666.example.com.  TXT   300  20.0: "test-dst"

[saikatharryc]

is this an example record that acts as poison pill?

test.dev-apps-gcloud-666.example.com.  TXT   300  20.0: "test-dst"

Yes that is,

gcloud dns --project=<GCP-PROJECT> record-sets create <XXX.XXX.XXX.com>. --zone="<DNS_ZONE>" --type="TXT" --ttl="300" --routing-policy-type="WRR" --routing-policy-item="weight=20.0,rrdatas=test"

[saikatharryc]

/ok-to-test

[ivankatliarchuk]

/lgtm

cc: @mloiseleur

[mloiseleur]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ivankatliarchuk, mloiseleur

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