Add remote-http online store

[tokoko]

Is your feature request related to a problem? Please describe.
Users can deploy http and grpc feature servers that wrap get_online_features calls, but currently there is no way to interact with feature servers from python sdk.

Describe the solution you'd like
Add online store types remote-http and remote-grpc (or maybe just call it a remote and differentiate with a url?) that wrap network calls to the respective feature servers. This follows the same pattern as remote registry implementation that wraps calls to the registry server.

[lokeshrangineni]

I am currently working on this and will get back in case if i find any difficulty.

[lokeshrangineni]

@franciscojavierarceo FYI

[franciscojavierarceo]

Some things we'll have to do:

1. Handle purely feature_views i.e., features="feature_view"
2. Handle feature references; i.e., ["feature_view:feature_1","feature_view:feature_2",...] etc.
3. Handle feature services

We'll have to serialize the data on the server to match what's in the feature registry from the FeatureView itself and fail loudly when it doesn't match, probably return a 400.

[tokoko]

@franciscojavierarceo I think you closed this by accident.

• Handle purely feature_views i.e., features="feature_view"

Is this something we support? The signature for get_online_features is only feature service or a list of features -> features: Union[List[str], FeatureService]

[franciscojavierarceo]

Whoops, nevermind that was based on outdated documentation I think.

[franciscojavierarceo]

@tokoko I'm confused about why we would do this? I think adding a client that makes the behavior intuitive makes sense but that's basically in the Python feature server.

[tokoko]

Well, it's more of convenience thing, i think. They can still use the feature server directly of course, but what this additional layer would enable is writing a piece of code using store.get_online_features and then configuring how you want to resolve features with feature_store.yaml. You could change the backend from the actual online store to http feature server or a grpc one without changing anything in the code itself.

[lokeshrangineni]

Few updates after started working on the issue:

1. There is no grpc implementation of APIs in python feature server. So this issue is going to only focus on remote with http implementation. We can enhance the online store to include grpc implementation when the grpc apis available on the python feature server.
2. Planning to implement the online store api methods of online_write_batch and online_read. Rest all life cycle methods of online_store are not having associated APIs in the feature server.

[dmartinol]

@tokoko can you confirm the above assumptions, in order to guide @lokeshrangineni 's implementation?

[tokoko]

sure, sounds like a good starting point.

[lokeshrangineni]

Created a draft PR just for initial feedback. Please note that code may change significantly depending on the feedback.
#4226