Support multiple identically-named zones

[coreypobrien]

In some cases, multiple identically-named zones exist for a single record. For example, an "example.com" private zone may be associated with a VPC in addition to a public "example.com" hosted zone. The ideal behavior for external-dns would be to update records for both the public zone (so that the record is publicly resolvable) and the private zone (so the record is resolvable inside the VPC).

Currently, the implementation of suitableZone (or its equivalent in other providers) returns only 1 longest-matching zone. I propose changing the default implementation to return a list of any longest-matching zones. The providers can then write the record to all of the zones returned.

As a part of changing this, we can tackle the consolidation of the suitable-zone logic for #228.

[coreypobrien]

The private hosted zones feature in AWS is actually semi-unique amongst the supported DNS providers. Supporting multiple results from suitableZone is actually a good example of AWS needing a specific implementation instead of a generic one. I'm removing the desire to consolidate that functionality from this issue.

[coreypobrien]

@njuettner @linki I'm curious to get your feedback on this and the work in #356. It conflicts with #263. I'd like to remove AWS from the consolidation since private hosted zones need to be treated differently. What do you all think?

[Shemeikka]

Hi,

What's the status of this issue/feature ?