CNAME targets stored as relative names when the trailing dot is missing

[stijzermans]

What happened?

External DNS normalizes targets by stripping the trailing dot (endpoint.NewEndpoint), so a target such as website.stackit.com. arrives at the webhook as website.stackit.com.

When trying to add the record website.not-stackit.com with a CNAME to website.stackit.com, STACKIT interprets a target (as sent through the webhook) without a trailing dot as relative to the zone, so the final record becomes: website.stackit.com.not-stackit.com. if DNS zone is not-stackit.com.

Other external-dns providers (Google) avoid this by ensuring hostname-valued targets end in a trailing dot. Relevant now that upstream external-dns explicitly accepts CNAME targets with a trailing dot: external-dns#6218.

How can we reproduce this?

Create an ingress with the following annotations:

external-dns.alpha.kubernetes.io/hostname: website.non-stackit.com
external-dns.alpha.kubernetes.io/target: website.stackit.com

This will create a CNAME for website.non-stackit.com with targetwebsite.stackit.com.non-stackit.com (on a DNS zone for non-stackit.com)
Expect it to be target website.stackit.com

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