generalcommission / aioprometheus

A Prometheus Python client library for asyncio-based applications

aioprometheus

aioprometheus is a Prometheus Python client library for asyncio-based applications. It provides metrics collection and serving capabilities, supports multiple data formats and pushing metrics to a gateway.

The project documentation can be found on ReadTheDocs.

Install

$ pip install aioprometheus

A Prometheus Push Gateway client and ASGI service are also included, but their dependencies are not installed by default. You can install them alongside aioprometheus by running:

$ pip install aioprometheus[aiohttp]

Prometheus 2.0 removed support for the binary protocol, so in version 20.0.0 the dependency on prometheus-metrics-proto, which provides binary support, is now optional. If you want binary response support, for use with an older Prometheus, you will need to specify the 'binary' optional extra:

$ pip install aioprometheus[binary]

Multiple optional dependencies can be listed at once, such as:

$ pip install aioprometheus[aiohttp,binary]

Example

The example below shows a single Counter metric collector being created and exposed via the optional aiohttp service endpoint.

#!/usr/bin/env python
"""
This example demonstrates how a single Counter metric collector can be created
and exposed via a HTTP endpoint.
"""
import asyncio
import socket
from aioprometheus import Counter, Service


if __name__ == "__main__":

    async def main(svr: Service) -> None:

        events_counter = Counter(
            "events", "Number of events.", const_labels={"host": socket.gethostname()}
        )
        svr.register(events_counter)
        await svr.start(addr="127.0.0.1", port=5000)
        print(f"Serving prometheus metrics on: {svr.metrics_url}")

        # Now start another coroutine to periodically update a metric to
        # simulate the application making some progress.
        async def updater(c: Counter):
            while True:
                c.inc({"kind": "timer_expiry"})
                await asyncio.sleep(1.0)

        await updater(events_counter)

    loop = asyncio.get_event_loop()
    svr = Service()
    try:
        loop.run_until_complete(main(svr))
    except KeyboardInterrupt:
        pass
    finally:
        loop.run_until_complete(svr.stop())
    loop.close()

In this simple example the counter metric is tracking the number of while loop iterations executed by the updater coroutine. In a realistic application a metric might track the number of requests, etc.

Following typical asyncio usage, an event loop is instantiated first then a metrics service is instantiated. The metrics service is responsible for managing metric collectors and responding to metrics requests.

The service accepts various arguments such as the interface and port to bind to. A collector registry is used within the service to hold metrics collectors that will be exposed by the service. The service will create a new collector registry if one is not passed in.

A counter metric is created and registered with the service. The service is started and then a coroutine is started to periodically update the metric to simulate progress.

This example and demonstration requires some optional extra to be installed.

$ pip install aioprometheus[aiohttp,binary]

The example script can then be run using:

(venv) $ cd examples
(venv) $ python simple-example.py
Serving prometheus metrics on: http://127.0.0.1:5000/metrics

In another terminal fetch the metrics using the curl command line tool to verify they can be retrieved by Prometheus server.

By default metrics will be returned in plan text format.

$ curl http://127.0.0.1:5000/metrics
# HELP events Number of events.
# TYPE events counter
events{host="alpha",kind="timer_expiry"} 33

Similarly, you can request metrics in binary format, though the output will be hard to read on the command line.

$ curl http://127.0.0.1:5000/metrics -H "ACCEPT: application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited"

The metrics service also responds to requests sent to its / route. The response is simple HTML. This route can be useful as a Kubernetes /healthz style health indicator as it does not incur any overhead within the service to serialize a full metrics response.

$ curl http://127.0.0.1:5000/
<html><body><a href='/metrics'>metrics</a></body></html>

The aioprometheus package provides a number of convenience decorator functions that can assist with updating metrics.

The examples directory contains many examples showing how to use the aioprometheus package. The app-example.py file will likely be of interest as it provides a more representative application example than the simple example shown above.

Examples in the examples/frameworks directory show how aioprometheus can be used within various web application frameworks without needing to create a separate aioprometheus.Service endpoint to handle metrics. The FastAPI example is shown below.

#!/usr/bin/env python
"""
Sometimes you may not want to expose Prometheus metrics from a dedicated
Prometheus metrics server but instead want to use an existing web framework.

This example uses the registry from the aioprometheus package to add
Prometheus instrumentation to a FastAPI application. In this example a registry
and a counter metric is instantiated and gets updated whenever the "/" route
is accessed. A '/metrics' route is added to the application using the standard
web framework method. The metrics route renders Prometheus metrics into the
appropriate format.

Run:

  $ pip install fastapi uvicorn
  $ uvicorn fastapi_example:app

"""

from aioprometheus import render, Counter, Registry
from fastapi import FastAPI, Header, Response
from typing import List


app = FastAPI()
app.registry = Registry()
app.events_counter = Counter("events", "Number of events.")
app.registry.register(app.events_counter)


@app.get("/")
async def hello():
    app.events_counter.inc({"path": "/"})
    return "hello"


@app.get("/metrics")
async def handle_metrics(response: Response, accept: List[str] = Header(None)):
    content, http_headers = render(app.registry, accept)
    return Response(content=content, media_type=http_headers["Content-Type"])

License

aioprometheus is released under the MIT license.

aioprometheus originates from the (now deprecated) prometheus python package which was released under the MIT license. aioprometheus continues to use the MIT license and contains a copy of the original MIT license from the prometheus-python project as instructed by the original license.