Add support for NodePort services

[grimmy]

Initial work towards support for NodePort services for #191.

I'm a little lost on how to get some fake nodes into the testing harness so any help would be appreciated. I also haven't been able to test this yet as my dev cluster is in bad shape at the moment.

Any input would be greatly appreciated. I went with a poll on update due to the rest of the application not using the event stream. This poll is done once and passed through the update process.

[linki]

Thanks for working on this @grimmy.

Adding some test Nodes is fairly easy. Just create them the same way as you create test Services (https://github.com/kubernetes-incubator/external-dns/pull/559/files#diff-8baa5800e3e2b291d315e890b1b15f48R1110) via the fake client.

Here is an example: https://github.com/linki/armor-ingress-controller/blob/master/controller/controller_test.go#L795-L817

[linki]

If it helps you can also look at how we did NodePorts in mate: https://github.com/linki/mate/blob/master/producers/node_ports.go (It looks very similar.)

[linki]

We have to rework the whole sync vs. watch approach (#484). However, let's tackle this independently and go with the current design for this feature.

My main concern is that the implementation fetches the NodeList for every Service on every iteration. This we should definitely avoid. I think one request for the node list in each interation is fine.

[grimmy]

Just wanted to ping here that I'm still working on this. I just updated it add an SRV record for each port in the service.

That said I still need to figure out how to handle clusters that don't have external addresses and how that ties into private dns zones.

Also the travis failure is unrelated to this PR, just a gofmt -s that slipped through and made it to master.

[grimmy]

@linki This should be good to go now. I'ved tested on my cluster with route 53 and everything is good. I set the priority to 0 and weight to 50 for now. The priority should be the same across the cluster and be fine at zero, but I put the weight at 50 just in case anyone needs to tinker with it for whatever reason.

[njuettner]

@linki WDYT? anything missing or can we merge this PR?

[linki]

LGTM, thanks a lot @grimmy 👍

[hjacobs]

@linki @njuettner does it mean that External DNS now has all features to replace kops' DNS controller?

[grimmy]

You're very welcome @linki thanks for the merge!! :-D