Support for external-dns

[Tommi2Day]

It would be nice to see also a netcup provider in kubernetes-external-dns . I would assume its very similar to your existing webhook implementation

[aellwein]

Interesting idea, didn't thought of that. I may give it a try, their provider implementation doesn't look like a big deal.

[aellwein]

Some notes about progress: ATM i'm trying to implement the external-dns provider interface. There is an obstacle to some content that netcup DNS API doesn't provide lookup on zones records being used -- because of this restriction, i decided that the domain filter parameter will always be mandatory (as a hint to the system which domains can be used).

[Tommi2Day]

Thx. Guess the named restrictions wont be a problem for me

[mrueg]

@aellwein are you still working on this? This would be a great addition :)

[aellwein]

@mrueg sorry for the delay, i've been busy lately.
I am still working on this, however, with a low prio until now.
I'll try to put more effort so that we can have a prototype for testing soon.

[mrueg]

@aellwein Happy to collaborate on that if you'd like.

[mrueg]

@aellwein fyi I think I made some progress on the ApplyChanges and used your code (hope you don't mind) in https://github.com/mrueg/external-dns/tree/add-netcup-provider
Still needs some more work and unit (and real life) tests.

[aellwein]

@mrueg great, i'm happy you made the progress and took the effort! I don't mind you used my previous work.
I'll take a look at it soon. Think we need some tutorial and also unit tests, like other providers do.
Good work!
Wish you a merry christmas.

[mrueg]

Thanks! I've also rebased on your latest commit to preserve attribution. Hope to give it a test in the next couple of days.

Merry christmas!

Edit: I've added some unit tests as well.

[aellwein]

@mrueg i took a quick look to your branch.
It looks good to me, basically the same approach i was taking, the only thing i've noticed that you've introduced a new flag "netcup-zones" for hinting the DNS zones in provider and my aim was to reuse existing "domain-filter" flag, as it was basically existing and is one of "generic" provider-independent flags.

I have no strong opinion whether the new flag is reasonable here, so it's okay with me.
At least this comment here needs to be changed as the domain filter is not being used.

I still need to test it in my own cluster to see how it behaves.

[mrueg]

Thanks for the feedback! I've removed the comment. I think the domainFilter has different semantics (e.g. you can't provide a regex to netcup's API to get the zones), so I've added a zones field.

I've added a tutorial here: https://github.com/kubernetes-sigs/external-dns/blob/20c217a1cabf95868025a8bf843149ce2ef9e336/docs/tutorials/netcup.md

[mrueg]

@aellwein I've tested it locally and it seems to work fine. I would be able to raise a PR and wanted to check in if you're okay with being listed as a maintainer as well?

[aellwein]

@mrueg 👍🏻 sure thing, count me in.
Just created a PR for your branch to remove some references to Plural DNS.
You can also squash those commits if you want.
Please proceed with a PR to mainstream repo.