Prometheus metrics in Sanic

Question

I'm trying to add metrics to my Sanic app. Prometheus provides Python client running as ASGI app - https://prometheus.github.io/client_python/exporting/http/asgi/ .

The question is how to run 2 ASGI apps at once.

I found Starlette could help:

from prometheus_client import make_asgi_app
from starlette.applications import Starlette
from starlette.routing import Mount
from sanic import Sanic
from sanic.response import text
sanic_app = Sanic("MyHelloWorldApp")
@sanic_app.get("/")
async def hello_world(request):
 return text("Hello, world.")
metrics_app = make_asgi_app()
routes = [
 Mount("/", app=sanic_app),
 Mount("/metrics", app=metrics_app)
]
app = Starlette(routes=routes)
if __name__ == "__main__":
 import uvicorn
 uvicorn.run(app, host="127.0.0.1", port=8000, log_level="info")

metrics_app mounted and works, but Sunic returns an exception:

sanic.exceptions.SanicException: Loop can only be retrieved after the app has started running. Not supported with `create_server` function

Does anybody know a more straightforward way to use Prometheus Client with ASGI Sanic?

Answer 1

I've just read https://pyk.medium.com/a-guide-to-instrument-sanic-application-part-1-193b3eb403a

The next works!

import prometheus_client as prometheus
@app.get("/metrics")
async def metrics(request):
 return text(prometheus.exposition.generate_latest().decode("utf-8"))