Microservices

[petrarca]

Hello,
is there any plan to support the micro service add-on like in go? Does anybody know an already existing implementation on top of nats-py?
Thank you!

[charbonnierg]

EDIT: I pushed the code to https://github.com/charbonats/nats-micro and made it closer to the go implementation.

FWIW I started writing an implementation in a single file here but life was pretty hectic the last 2 months for me so did not have time to continue further (there are many files in the repo, but this file in particular does not import anything aside from standard library and nats-py). There's no test so I would not use it as anything else than an inspiration. I tried to adhere to:

• ADR-32: Service API.
• the reference implementation in nats.go under micro package.

But took some liberties (like the Nats-Service-Success-Code oddity). The Go package uses an interface for micro.Request, so I did something similar in this implementation. I think it might ease writing unit tests for handlers.

[charbonnierg]

Actually not much. You can compare:

• The Request class in python and in go. Signatures are different but I believe that the two implementations are equivalent feature-wise (with an additional status code header for successful response in my implementation)
• The Service class in python and in go. Again methods signature differ, but except for the Reset() method which is missing on my implementation, I believe that they are equivalent feature wise.
• The Group class in python and in go. Again signature differ, but it's possible to add sub-groups and endpoints to a group.

To sum up, I would say that I did not follow closely enough the ADR and did not implement a reset() method, but aside from that there's not much difference ?

[charbonnierg]

I pushed the code to https://github.com/charbonats/nats-micro:

Example usage below, click to unfold:

"""Minimal example of NATS micro usage."""

import asyncio
import contextlib
import signal

from nats.aio.client import Client

import micro


async def echo(req: micro.Request) -> None:
    """Echo the request data back to the client."""
    await req.respond(req.data())


async def main():
    # Define an event to signal when to quit
    quit_event = asyncio.Event()
    # Attach signal handler to the event loop
    loop = asyncio.get_event_loop()
    for sig in (signal.Signals.SIGINT, signal.Signals.SIGTERM):
        loop.add_signal_handler(sig, lambda *_: quit_event.set())
    # Create an async exit stack
    async with contextlib.AsyncExitStack() as stack:
        # Create a NATS client
        nc = Client()
        # Connect to NATS
        await nc.connect("nats://localhost:4222")
        # Push the client.close() method into the stack to be called on exit
        stack.push_async_callback(nc.close)
        # Push a new micro service into the stack to be stopped on exit
        # The service will be stopped and drain its subscriptions before
        # closing the connection.
        service = await stack.enter_async_context(
            micro.create_service(
                nc,
                name="demo-service",
                version="1.0.0",
                description="Demo service",
            )
        )
        group = service.group("demo")
        # Add an endpoint to the service
        await group.add_endpoint(
            name="echo",
            handler=echo,
        )
        # Wait for the quit event
        await quit_event.wait()


if __name__ == "__main__":
    asyncio.run(main())

Output of nats micro ls:

╭──────────────────────────────────────────────────────────────────╮
│                        All Micro Services                        │
├──────────────┬─────────┬──────────────────────────┬──────────────┤
│ Name         │ Version │ ID                       │ Description  │
├──────────────┼─────────┼──────────────────────────┼──────────────┤
│ demo-service │ 1.0.0   │ ec17c596d93a7f3dafce9570 │ Demo service │
╰──────────────┴─────────┴──────────────────────────┴──────────────╯

Output of nats micro info demo:

Service Information

          Service: demo-service (ec17c596d93a7f3dafce9570)
      Description: Demo service
          Version: 1.0.0

Endpoints:

               Name: echo
            Subject: demo.echo
        Queue Group: q

Statistics for 1 Endpoint(s):

  echo Endpoint Statistics:

           Requests: 0 in group q
    Processing Time: 0s (average 0s)
            Started: 2024-02-17 13:51:46 (51.15s ago)
             Errors: 0

  Endpoint Specific Statistics:

After calling the service with nats req demo.echo foo, I run nats micro stats info and I get:

╭────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│                                     demo-service Service Statistics                                    │
├──────────────────────────┬──────────┬──────────┬─────────────┬────────┬─────────────────┬──────────────┤
│ ID                       │ Endpoint │ Requests │ Queue Group │ Errors │ Processing Time │ Average Time │
├──────────────────────────┼──────────┼──────────┼─────────────┼────────┼─────────────────┼──────────────┤
│ ec17c596d93a7f3dafce9570 │ echo     │ 1        │ q           │ 0      │ 72µs            │ 72µs         │
├──────────────────────────┼──────────┼──────────┼─────────────┼────────┼─────────────────┼──────────────┤
│                          │          │ 1        │             │ 0      │ 72ΜS            │ 72ΜS         │
╰──────────────────────────┴──────────┴──────────┴─────────────┴────────┴─────────────────┴──────────────╯

[petrarca]

Thank you very much!!! Would be great, if your work can be integrated into nats-py.

[petrarca]

Works great, any idea why "nats micro ls" and "... info" does not work: "No micro instances found".

[charbonnierg]

Nope no idea, those commands run fine on my computer with a local NATS server. I tried with the latest NATS CLI version. I updated my repo BTW, and tried to remove the gap with the go implementation. Some methods and functions changed.

EDIT: I understand what you meant now, thanks for the PR