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starlette_exporter

Prometheus exporter for Starlette and FastAPI

starlette_exporter collects basic metrics for Starlette and FastAPI based applications:

  • Counter: starlette_requests_total
  • Histogram: starlette_request_duration_seconds

Metrics include labels for the HTTP method, the path, and the response status code.

starlette_requests_total{method="GET",path="/",status_code="200"} 1.0
starlette_request_duration_seconds_bucket{le="0.01",method="GET",path="/",status_code="200"} 1.0

Use the HTTP handler handle_metrics at path /metrics to expose a metrics endpoint to Prometheus.

Table of Contents

  1. Usage
    1. Starlette
    2. FastAPI
  2. Options
  3. Custom metrics
  4. Multiprocess mode (gunicorn deployments)
  5. Developing
  6. License

Usage

pip install starlette_exporter

Starlette

from starlette.applications import Starlette
from starlette_exporter import PrometheusMiddleware, handle_metrics

app = Starlette()
app.add_middleware(PrometheusMiddleware)
app.add_route("/metrics", handle_metrics)

...

FastAPI

from fastapi import FastAPI
from starlette_exporter import PrometheusMiddleware, handle_metrics

app = FastAPI()
app.add_middleware(PrometheusMiddleware)
app.add_route("/metrics", handle_metrics)

...

Options

app_name: Sets the value of the app_name label for exported metrics (default: starlette).

prefix: Sets the prefix of the exported metric names (default: starlette).

group_paths: setting this to True will populate the path label using named parameters (if any) in the router path, e.g. /api/v1/items/{item_id}. This will group requests together by endpoint (regardless of the value of item_id). This option may come with a performance hit for larger routers. Default is False, which will result in separate metrics for different URLs (e.g., /api/v1/items/42, /api/v1/items/43, etc.).

filter_unhandled_paths: setting this to True will cause the middleware to ignore requests with unhandled paths (in other words, 404 errors). This helps prevent filling up the metrics with 404 errors and/or intentially bad requests. Default is False.

buckets: accepts an optional list of numbers to use as histogram buckets. The default value is None, which will cause the library to fall back on the Prometheus defaults (currently [0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1.0, 2.5, 5.0, 7.5, 10.0]).

Example:

app.add_middleware(PrometheusMiddleware, app_name="hello_world", group_paths=True, prefix='myapp', buckets=[0.1, 0.25, 0.5])

Custom Metrics

starlette_exporter will export all the prometheus metrics from the process, so custom metrics can be created by using the prometheus_client API.

Example:

from prometheus_client import Counter
from starlette.responses import RedirectResponse

REDIRECT_COUNT = Counter("redirect_total", "Count of redirects", ("from",))

async def some_view(request):
    REDIRECT_COUNT.labels(from="some_view").inc()
    return RedirectResponse(url="https://example.com", status_code=302)

The new metric will now be included in the the /metrics endpoint output:

...
redirect_total{from="some_view"} 2.0
...

Multiprocess mode (gunicorn deployments)

Running starlette_exporter in a multiprocess deployment (e.g. with gunicorn) will need the PROMETHEUS_MULTIPROC_DIR env variable set, as well as extra gunicorn config.

For more information, see the Prometheus Python client documentation.

Developing

git clone https://github.com/stephenhillier/starlette_exporter
cd starlette_exporter
pytest tests

License

Code released under the Apache License, Version 2.0.

Dependencies

https://github.com/prometheus/client_python

https://github.com/encode/starlette

Credits

Starlette - https://github.com/encode/starlette

FastAPI - https://github.com/tiangolo/fastapi

Flask exporter - https://github.com/rycus86/prometheus_flask_exporter

Alternate Starlette exporter - https://github.com/perdy/starlette-prometheus


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