aioprometheus

A Prometheus Python client library for asyncio-based applications

Project description

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

Example

The example below shows a single Counter metric collector being created and exposed via a HTTP 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.

The example script can 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 this 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.

There 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 that the simple example shown above.

Examples in the examples/frameworks directory show how aioprometheus can be used within existing aiohttp, quart and vibora applications instead of creating a separate aioprometheus.Service endpoint to handle metrics. The vibora example is shown below.

#!/usr/bin/env python
"""
Sometimes you want to expose Prometheus metrics from within an existing web
service and don't want to start a separate Prometheus metrics server.

This example uses the aioprometheus package to add Prometheus instrumentation
to a Vibora application. In this example a registry and a counter metric is
instantiated. A '/metrics' route is added to the application and the render
function from aioprometheus is called to format the metrics into the
appropriate format.
"""

from aioprometheus import render, Counter, Registry
from vibora import Vibora, Request, Response


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


@app.route("/")
async def hello(request: Request):
    app.events_counter.inc({"path": "/"})
    return Response(b"hello")


@app.route("/metrics")
async def handle_metrics(request: Request):
    """
    Negotiate a response format by inspecting the ACCEPTS headers and selecting
    the most efficient format. Render metrics in the registry into the chosen
    format and return a response.
    """
    content, http_headers = render(app.registry, [request.headers.get("accept")])
    return Response(content, headers=http_headers)


app.run()

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 orignal MIT license from the prometheus-python project as instructed by the original license.