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A Prometheus Python client library for asyncio-based applications

Project description

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aioprometheus is a Prometheus Python client library for asyncio-based applications. It provides metrics collection and serving capabilities for use with Prometheus and compatible monitoring systems. It supports exporting metrics into text and binary formats and pushing metrics to a gateway.

The ASGI middleware in aioprometheus can be used in FastAPI/Starlette and Quart applications. aioprometheus can also be used in other kinds of asyncio applications too.

The project documentation can be found on ReadTheDocs.

Install

$ pip install aioprometheus

The ASGI middleware does not have any external dependencies but the Starlette and Quart convenience functions that handle metrics requests do.

If you plan on using the ASGI middleware in a Starlette / FastAPI application then you can install the extra dependencies alongside aioprometheus by adding extras to the install.

$ pip install aioprometheus[starlette]

If you plan on using the ASGI middleware in a Quart application then you can install the extra dependencies alongside aioprometheus by adding extras to the install.

$ pip install aioprometheus[quart]

A Prometheus Push Gateway client and a HTTP service are included, but their dependencies are not installed by default. You can install them alongside aioprometheus by adding extras to the install.

$ 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 need 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,starlette,quart]

Usage

There are two basic steps involved in using aioprometheus; the first is to instrument your software by creating metrics to monitor events and the second is to expose the metrics to a collector.

Creating a new metric is easy. First, import the appropriate metric from aioprometheus. In the example below it’s a Counter metric. Next, instantiate the metric with a name and a help string. Finally, update the metric when an event occurs. In this case the counter is incremented.

from aioprometheus import Counter

events_counter = Counter(
    "events_counter",
    "Total number of events.",
)

events_counter.inc({"kind": "event A"})

By default, metrics get registered into the default collector registry which is available at aioprometheus.REGISTRY.

A number of convenience decorator functions are included in aioprometheus that can assist with automatically updating metrics. The examples directory contains various decorators examples.

Once your software is instrumented with various metrics you’ll want to expose them to Prometheus or a compatible metrics collector. There are multiple strategies available for this and the right choice depends on the kind of thing being instrumented.

If you are instrumenting a Starlette, FastAPI or Quart application then the easiest option for adding Prometheus metrics is to use the ASGI Middleware provided by aioprometheus.

The ASGI middleware provides a default set of metrics that include counters for total requests received, total responses sent, exceptions raised and response status codes for route handlers.

The example below shows how to use the aioprometheus ASGI middleware in a FastAPI application. FastAPI is built upon Starlette so using the middleware in Starlette would be the same.

from fastapi import FastAPI, Request, Response

from aioprometheus import Counter, MetricsMiddleware
from aioprometheus.asgi.starlette import metrics

app = FastAPI()

# Any custom application metrics are automatically included in the exposed
# metrics. It is a good idea to attach the metrics to 'app.state' so they
# can easily be accessed in the route handler - as metrics are often
# created in a different module than where they are used.
app.state.users_events_counter = Counter("events", "Number of events.")

app.add_middleware(MetricsMiddleware)
app.add_route("/metrics", metrics)


@app.get("/")
async def root(request: Request):
    return Response("FastAPI Middleware Example")


@app.get("/users/{user_id}")
async def get_user(
    request: Request,
    user_id: str,
):
    request.app.state.users_events_counter.inc({"path": request.scope["path"]})
    return Response(f"{user_id}")


if __name__ == "__main__":
    import uvicorn

    uvicorn.run(app)

Other examples in the examples/frameworks directory show how aioprometheus can be used within various web application frameworks.

The next example shows how to use the Service HTTP endpoint to provide a dedicated metrics endpoint for other applications such as long running distributed system processes.

#!/usr/bin/env python
"""
This example demonstrates how the ``aioprometheus.Service`` can be used to
expose metrics on a HTTP endpoint.

.. code-block:: console

    (env) $ python simple-service-example.py
    Serving prometheus metrics on: http://127.0.0.1:8000/metrics

You can open the URL in a browser or use the ``curl`` command line tool to
fetch metrics manually to verify they can be retrieved by Prometheus server.

"""

import asyncio
import socket

from aioprometheus import Counter
from aioprometheus.service import Service


async def main():

    service = Service()
    events_counter = Counter(
        "events", "Number of events.", const_labels={"host": socket.gethostname()}
    )

    await service.start(addr="127.0.0.1", port=8000)
    print(f"Serving prometheus metrics on: {service.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)

    # Finally stop server
    await service.stop()


if __name__ == "__main__":

    try:
        asyncio.run(main())
    except KeyboardInterrupt:
        pass

A counter metric is used to track the number of while loop iterations executed by the ‘updater’ coroutine. The Service is started and then a coroutine is started to periodically update the metric to simulate progress.

The Service can be configured to bind to a user defined network interface and port.

When the Service receives a request for metrics it forms a response by rendering the contents of its registry into the appropriate format. By default the Service uses the default collector registry, which is aioprometheus.REGISTRY. The Service can be configured to use a different registry by passing one in as an argument to the Service constructor.

The Service object requires optional extras to be installed so make sure you install aioprometheus with the ‘aiohttp’ extras.

$ pip install aioprometheus[aiohttp]

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.

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