Federation extension related "warning" on UDP support

[soxofaan]

@christophfriedrich a quick note on your demo earlier today regarding the federation extension related warning on the "User-Defined Processes" (UDP):

As you mentioned yourself I think, it's a bit misleading to mark the services "unavailable" as a whole, while this is just about the UDP aspect.

Moreover, this is actually not a problem of these backends themselves, but a limitation in the current implementation of openeo-aggregator. The aggregator only considers a single backend (e.g. VITO in case of openeo.cloud) for the CRUD actions of the user-defined-processes sub-API. The other backends (e.g. EODC/ SentinelHub from screenshot above) are not even attempted.

For more background, see:

• UDP support in a federation context? openeo-aggregator#176

[m-mohr]

The client can't know the details, I think this is an aggregator issue and should be solved there. I'm also wondering whether a backend should actually be listed there if it doesn't support a functionality at all, I think we had seen that in some cases. For example, if Sinergise doesn't support UDP or jobs at all, it should probably not be listed in the federation:missing, I think.

The only thing we can do here is to slightly rephrase to e.g.

This data is potentially incomplete as the following services in the federation are not fully available: ...

[christophfriedrich]

Yeah, I think there are several things wrong with the current wording:

• Backends are accused of being entirely unavailable while it may actually be only a sub-service that's missing
• It's attributed to an outage, while the presence of federation:missing actually only tells us that certain backends are missing from the response, not saying anything about the "why"
• It's implied that this is a temporal situation, while it may actually be long-term in case when the backend doesn't support that sub-service and doesn't plan to change that either (e.g. jobs on Sentinel Hub)
• It's stated that the data "is" incomplete, while we actually don't know if there even is any more data on the missing component -> "may" would be more appropriate
• As you state, the limitation might even be in the aggregator, so it's not really fair to "blame" certain backends

-> Overall, I think the following rewording might overcome these issues by just stating the fact without speculating on any reasons:

This data may be incomplete as it does not include the following services in the federation: ...

[m-mohr]

The spec says that federation:missing is used when a backend is "not available", that implies offline to me and is reflected in the wording in the Vue components.
Although the list endpoints are not listed explicitly, I think federation:backends should be used if only a subset of backends support the resource. (But this is more an aggregator and API issue rather than a Vue issue at this point.)

[christophfriedrich]

Hm okay, you've got a point: federation:backends is to be used to signal general support, federation:missing for temporary deviations from that. We should significantly update the federation extension spec to explain this better.

For the components, I think rewording to this would do it justice:

This data may be incomplete as currently the following services in the federation are not fully available: ...

[soxofaan]

The spec says that federation:missing is used when a backend is "not available", that implies offline to me and is reflected in the wording in the Vue components.

In the spec I see about federation:missing:

Lists all back-ends that were not considered in the response (e.g. because they were not accessible).

Being unavailable in this description is just an example as a reason for "not being considered".
In this case of UDP support, the aggregator, in its current implementation, is internationally not considering some backends (for technical reasons that are not highly relevant for this discussion). So in my reading of the spec, it seems correct for the aggregator to lists these backends under federation:missing (regardless if they are on/offline, if they support the UDP sub-API or not, ...)

[m-mohr]

Yes and no.

Reading the whole extension also give a way to express which backends actually support a certain functionality, which is federation:backends ("Resources supported only by a subset of back-ends").

federation:missing is meant more as a temporary thing, where backends are temporarily not having such information (e.g. because they are having issues). Otherwise, such warnings about missing backends would be shown always in clients. Depending on whether that's intentional or not, you could list them. But I'm not sure whether it's overly helpful to always show a warning to users that a certain backend doesn't support e.g. files or UDPs.

I guess we need to issue a clarification. See Open-EO/openeo-api#564

[m-mohr]

Closing in favor of Open-EO/openeo-api#564.
If there are other more specific things to work on in the Vue Components, let's open a separate issue.