Enhance --domain-filter to match parent zones too

[euven]

What would you like to be added:

Currently it is not possible to use the --domain-filter to match against a parent zone. For example, if we had a registered "parent" zone example.com and we then set --domain-filter=x.example.com, then example.com will not be determined as a matching zone here.

It would provide more flexibility if --domain-filter could consider parent zones as matches too.

Why is this needed:

Having --domain-filter match parent zones:

1. would allow the providers to apply finer-grained control over DNS generation for sub domains within the same zone, i.e --domain-filter=x.example.com would create a DNS entry for x.example.com (and subdomains thereof), but y.example.com could be blocked/ignored;
2. would mean that one wouldn't be required to register "child" zones

Please let me know if this is something that sounds feasible and would be worth adding, or if I'm totally missing the point :)

Thanks for this great tool!

[rektide]

I feel like I'm missing something (but I'm very new here)? Why not just set --domain-filter=example.com ?

[evhan]

We have a use case where this would help. In our situation we have a single zone, and we want to manage multiple domains within that zone using separate instances of ExternalDNS so that we can configure their behaviours differently (different TXT owner details, publishing settings, etc.).

We'd expected the --domain-filter flag to let us do this, but like @bynare says it seems to instead behave more like a "zone filter" in that it will only consider whether a given record is in a zone argument; if the argument is a domain it will not work. Ideally we'd be able to run two instances of ExternalDNS, one for each of (for example) --domain-filter=x.example.com and --domain-filter=y.example.com, and their effects would be scoped to those domains regardless of whether they represent separate zones or are just two domains in the same zone.

[rafatio]

We have a similar scenario here, we want to only enable the creation of specific subdomains for different ExternalDNS instances. For example, we are using the aws provider with the hosted zone example.com. In instance A we want to use --domain-filter=a.example.com to only enable the creation of *.a.example.com. In instance B we want to use --domain-filter=b.example.com to only enable the creation of *.b.example.com. But the --domain-filter is also being applied in the zones here, because of that it fails without any available zones.
It really needs to apply this --domain-filter in the zones? Shouldn't the suitableZones function be enough to filter the zones?