Alias to CNAME record type changes failed

[moskitone]

What happened:
New feature provided by #1867 does not work with some EKS endpoints.
We have bunch of ingresses covered by nginx-ingress and AWS NLB.
In current setup we have lots of A(alias) records in route53 zones. After upgrading external-dns to 8.0.0 and setting --aws-prefer-cname nothing has changed.
We can see lots of records in logs like
time="2021-05-26T12:53:22Z" level=debug msg="Adding bbb.aaaaaa.io. to zone aaaaaa.io. [Id: /hostedzone/ZYaaaaaa]"
time="2021-05-26T12:53:23Z" level=info msg="Desired change: UPSERT bbb.aaaaaa.io CNAME [Id: /hostedzone/ZYaaaaaa]"
time="2021-05-26T12:53:23Z" level=error msg="InvalidChangeBatch: [RRSet of type CNAME with DNS name bbb.aaaaaa.io. is not permitted as it conflicts with other records with the same DNS name in zone aaaaaa.io.]\n\tstatus code: 400, request id: 09e0b116-..."
time="2021-05-26T13:00:36Z" level=debug msg="Endpoints generated from ingress: NS/INGRESS: [bbb.aaaaaa.io 0 IN CNAME ae...-4da9....elb.us-west-2.amazonaws.com [] bbb.aaaaaa.io 0 IN CNAME ae...-4da9....elb.us-west-2.amazonaws.com []]"

What you expected to happen:
Old A record is replaced with new CNAME
Environment:

• External-DNS version (use external-dns --version): 8.0.0
• DNS provider: AWS route53

[jsravn]

@moskitone so the old records are ALIAS, and you are trying to convert them to plain CNAME? external-dns never used to check record types at all up until #1867, so I don't see how it could have worked prior either.

external-dns can't currently differentiate between alias and cname records, so the --aws-prefer-cname flag is used to tell it what to use. If you were using ALIAS then add that flag, it will break unfortunately. To fix that, we'd need to introduce the concept of aliases more generically in external-dns.

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