Move kops-controller client into its own package

[justinsb]

This should allow more reuse.

[johngmyers]

I can see moving Client and dial, but I'd prefer we leave the bootstrap-specific portions of QueryBootstrap behind. Perhaps pass in a req, resp interface{}?

Possibly pass in the authenticator as well, since non-bootstrap requests will probably have a different authenticator?

[johngmyers]

Actually, req and resp should use type parameters. No need to pass in a resp.

[justinsb]

I don't think we can use type parameters today with struct methods (unless you know a trick).

I'm guessing you want to not move nodeup.BootstrapRequest because of versioning skew issues? But we do have those skew issues, I think. Although maybe if we always update the control plane first, and don't bootstrap control-plane nodes, it's not a problem in practice?

This refactor is to support updating gossip to just work through kops-controller. For that I was thinking of using GRPC, because I think we want streaming support rather than polling. I could just leave the existing QueryBootstrap client/logic where it is and make this a pure GRPC client - that would work too. A bit of a code duplication for connecting, but not too bad as the GRPC interfaces are a little different anyway. Would that be better for you?

[johngmyers]

I sent you a PR to remove knowledge of the request and response types. I think it would be good to make the authenticator optional and possibly passed-in per request.

I see there are two bootstrap requests to kops-controller. It would be good to consolidate them, preferably into the one that is a Task. But that is probably a different PR.

[johngmyers]

I don't want to move BootstrapRequest because I don't want that knowledge outside of nodeup. It should be obvious that only nodeup can bootstrap or authenticate as a bootstrapping instance.

If you need GRPC features, then I suppose you need GRPC. I'd prefer to keep the bootstraprequest simple if possible, so that we can reason about its security. You could probably extract the connection logic into something shared by the REST and GRPC query methods.

[justinsb]

Thanks @johngmyers - pulled in your change :-)

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