Connexion 3.0 and Prometheus

[danielbprice]

I have been trying without much success to plug together aioprometheus==23.3.0 and connexion==3.0.1[swagger-ui,uvicorn]. The closest I can get is as follows:

  from pathlib import Path

  import connexion

  from starlette.responses import Response
  from starlette.requests import Request

  from aioprometheus import MetricsMiddleware
  from aioprometheus import REGISTRY, render

  # Cribbed from aioprometheus.  This is needed because the builtin aioprometheus starlette helper
  # references request.app.state, which fails under Connexion.
  async def metrics(request: Request) -> Response:
      """Render metrics into format specified by 'accept' header.
      """
      content, http_headers = render(REGISTRY, request.headers.getlist("Accept"))
      return Response(content=content, media_type=http_headers["Content-Type"])

  async def test():
      pass

  async def post_greeting(name: str):
      await test()
      return f"Hello {name}", 201

  app = connexion.AsyncApp(__name__, specification_dir="spec")
  app.add_api("openapi.yaml", arguments={"title": "Hello World Example"})

  # Here is where we diverge from the example app setup
  app.add_middleware(MetricsMiddleware)
  app.add_url_rule("/metrics", view_func=metrics)

  if __name__ == "__main__":
      app.run(f"{Path(__file__).stem}:app", port=8080)

What I find if I run this is that every request traces back. This is because the MetricsMiddleware is trying to inspect some attributes of what it thinks is a starlette, but is really a ConnexionMiddleware:

INFO:     Application startup complete.
AttributeError("'ConnexionMiddleware' object has no attribute 'routes'")
Traceback (most recent call last):
  File "/home/dp/venv-xx/lib/python3.10/site-packages/starlette/_exception_handler.py", line 44, in wrapped_app
    await app(scope, receive, sender)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/swagger_ui.py", line 220, in __call__
    await self.router(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/starlette/routing.py", line 775, in __call__
    await self.default(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/swagger_ui.py", line 233, in default_fn
    await self.app(original_scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/routing.py", line 153, in __call__
    await self.router(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/starlette/routing.py", line 775, in __call__
    await self.default(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/routing.py", line 47, in __call__
    await self.next_app(original_scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/abstract.py", line 272, in __call__
    await self.app(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/abstract.py", line 272, in __call__
    await self.app(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/abstract.py", line 272, in __call__
    await self.app(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/connexion/middleware/lifespan.py", line 26, in __call__
    await self.next_app(scope, receive, send)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/aioprometheus/asgi/middleware.py", line 175, in __call__
    path = self.get_full_or_template_path(scope)
  File "/home/dp/venv-xx/lib/python3.10/site-packages/aioprometheus/asgi/middleware.py", line 216, in get_full_or_template_path
    for route in self.starlette_app.routes:
AttributeError: 'ConnexionMiddleware' object has no attribute 'routes'
INFO:     127.0.0.1:54772 - "GET /anything HTTP/1.1" 500 Internal Server Error

The failing routine inside of MetricsMiddleware looks like this (https://github.com/claws/aioprometheus/blob/master/src/aioprometheus/asgi/middleware.py#L213):

        if self.use_template_urls:
            if self.starlette_app:
                # Extract the route template from Starlette / FastAPI apps
                for route in self.starlette_app.routes:                     # <---------
                    match, _child_scope = route.matches(scope)
                    # Enum value 2 represents the route template Match.FULL
                    if match.value == 2:
                        return route.path

I found that subclassing MetricsMiddleware and setting self.use_template_urls = False does enable things to work, however then you lose coalescing of metrics by route.

I was wondering if anyone else has successfully built a Connexion + Prometheus setup. I am not wedded to aioprometheus.

If there is a good recipe out there, could the authors add it to the cookbook please? This could save a lot of pain and suffering.

[RobbeSneyders]

Hi @danielbprice,

Connexion sets scope["app"] here, which is then used by the Prometheus Middleware.

We could either:

• Set the Starlette router we use as scope["app"] so the Prometheus middleware can use it
• Create a Connexion-specific ASGI middleware that handles a ConnexionMiddleware
• Mimick the interface of a Starlette application with the ConnexionMiddleware

Not yet sure which is the best approach.

We can find the Starlette router used by Connexion like this:

for middleware in self.middleware_stack:
    if isinstance(middleware, RoutingMiddleware):
        router = middleware.router

For any of the possible approaches mentioned above, this should be enough info to get it to work. We would appreciate it if you could try it out and report back.

FYI, there's two Prometheus middleware that work with starlette:

• https://github.com/perdy/starlette-prometheus/tree/master
• https://github.com/claws/aioprometheus/tree/master

[danielbprice]

Thanks for the reply. I will take another lap on this after I catch up with the 3.0.2 release.