Run EOEPCA externally

[m-mohr]

As a demo for the tiger team meetings, very basic for now.

Open question:

• Authentication (requires a non-interactive authentication workflow on side of EOEPCA)
• How to transfer data cubes forth and back?
• Same issues as for UDFs apply (e.g. chunking) or the full result needs to be transferred (likely the latter)
• ...

Rendered variant for better readability:

[jdries]

I guess you'll also want to define the interface that your EOEPCA process needs to support to be callable by openEO? EOEPCA processes are fully generic AFAIK, so I guess they need to be more specific if we'd want to call them from openEO.

Note that we have done the other way around: calling openEO from EOEPCA processes is super easy and allows for some nice use cases where the EOEPCA process can do multiple calls to openEO, or advanced pre/post processing.

[m-mohr]

Hmm... I thought OGC API - Processes is the interface? Maybe I misunderstood.

We should probably mention that the other way around might be better defined and easier to do.

Context: We were asked by Guenther Landgraf how it could work to call EOEPCA from openEO, so this is more a demo/conceptish thing rather than a final proposal.

[jdries]

Note that from a user perspective, calling an external service may not be necessary. In fact, if there's an application package that satisfies a few conditions, an openEO backend can use it in a way that's very similar to our UDF setup. This would also avoid having to solve the problem of authentication between these services.