Add Service API

[Jarema]

Proposed change

Implement Service API spec: https://github.com/nats-io/nats-architecture-and-design/blob/main/adr/ADR-32.md

Use case

Simplify the development of NATS micro-services.

The design goal of the API is to reduce development to having a complexity similar to that of writing a NATS subscription, but then by using simple configuration, allow the specified metadata to allow for standardization of discovery and observability.

[yash97]

Hi can i work on this problem?

[Jarema]

Hi @yash97

Contributions are very welcome!
However there is some work in progress. Let me find the branch and see if there was progress recently to avoid any duplication of efforts.

[charbonnierg]

You might want to check https://github.com/charbonats/nats-micro

There are some tests: https://github.com/charbonats/nats-micro/blob/main/tests/test_micro.py

Note that I created https://github.com/charbonats/nats-request-many and it's used as a dependency. It's also tested: https://github.com/charbonats/nats-request-many/blob/next/tests/test_request_many.py.

EDIT: In no case I'm suggesting to use my library, instead I'm suggesting it as an inspiration for writing a PR. We're using this library at work for a new product without problem fow now, but we did not put it in production yet.

Also, I'm convinced that a CLI is a game changer for this feature and I hope that this would be introduced in nats-py. Having no "standard way" to run a nats micro service is not harmful to existing NATS users, but may refrain new users from using this feature. It would be awesome to be able to start a NATS app as easily as you can start an ASGI or WSGI application using uvicorn/gunicorn today. I tried to come up with a solution in my library, you can see the example usage: https://charbonats.github.io/nats-micro/#example-usage. I'm not convinced it's the correct design, but it has proven to be extremely useful for quick prototyping at work. @Jarema , @wallyqs maybe you have an opinion on this subject ?