Introduces EurekaRegistrationFeature

[ljnelson]

This PR introduces EurekaRegistrationFeature to implement the goals described in #9704.

Documentation will follow once the PR stabilizes.

[tjquinno]

A few comments/questions/corrections.

[tjquinno]

Does our code default the port to 8761 if the user does not specify it? Should we?

Maybe the doc should say either way.

[ljnelson]

My thinking here is that the Eureka server is out of our control, so we should leave defaults alone. What say you?

[tjquinno]

Ah, so if we don't set the value in the Eureka API then Eureka applies its defaults.

Maybe the doc can say just that?

[ljnelson]

Well, there aren't any defaults to apply here. You have to set the base-uri using the HttpClientConfig API (via configuration). If you don't, the integration doesn't know where the Eureka server is. I spent a while reverse engineering some things on the Eureka side to figure out what this URI should look like and wanted to save someone else the pain. There's no requirement that the Eureka server expose itself on port 8761, or that its context path be /eureka, but those do seem to be common values encountered in the wild. Open to suggestions on how to convey all this.

[tjquinno]

I was thinking from a user's perspective, not necessarily from how the Helidon code decides to implement the configuration (which, don't get me wrong, as written, makes perfect sense). For a generic HTTP server there's no requirement that it listen on port 80, but that's common so users might expect to be able to omit that from configuration specifying a URI to a generic webserver.

In the context of our Eureka integration, I was imagining that the user is thinking about specifying how to connect to a Eureka server, and if port 8761 is common (though not required) it seems to me that such a user would be thinking "the Helidon integration will connect using port 8761 if I don't specify otherwise."

My doc point was that, if our code is not providing the common port as a default then the doc maybe could say "The base-uri needs to identify the full URI--including host, port, and path-- to an available Netflix Eureka Server" (italics just for emphasis in this comment and there might be better phrases to convey this). That's implied by the next sentence in the doc which says this client config is wholly defined by HttpClientConfig, implied so long as a reader reads that and thinks "oh, yes, that's for a connecting to a generic webserver which would use a default port of 80 but I don't want 80 so I'd better specify 8761."

I guess I do not expect readers thinking about setting up config for connecting to a Eureka server to have the above realization on their own, hence my search for some way to emphasize this.

[ljnelson]

a user would be thinking "the Helidon integration will connect using port 8761 if I don't specify otherwise."

Right, but unless I'm missing something that would involve my checking the Http1ClientBuilder's baseUri property, cracking it open to see what the port is, and then filling in the details for what was, in all other respects, a fully-specified base URI value. Was it truly fully specified? Or not? How could I tell? I think this is a limitation (one of many) in the configuration mechanism, but if the baseUri property is treated as atomic, I think I have to respect it.

[tjquinno]

I originally thought that it might be simpler than it turns out for Helidon to apply Eureka-endpoint defaults to omitted portions of the URI but I have seen the light that this would be more involved than is worth it.

That's why my latest comment shifted to suggesting the doc emphasize that the user should not assume that Helidon will supply Eureka-inspired defaults to omitted parts of the URI. But I tried to phrase it in a positive way ("specify the entire URI") instead of a negative way ("don't expect us to default the port or path for you").

[ljnelson]

Got it; so either as part of this PR (if there's time, not sure) or a follow-on I should change the base URI documentation to indicate that it should fully identify a Eureka server (scheme, host, port, context path), and perhaps offer a quick example.

[ljnelson]

How about if (now or later) I change the relevant part of that .adoc file to read:

<3> The base-uri needs to identify an available Netflix Eureka Server of at least version {version-lib-eureka}. The URI must be absolute, and must specify a scheme (often https), a host, a port (often 8761), and a path identifying the root of a Netflix Eureka Server installation (often /eureka).

…?

[tjquinno]

Superb!