starlette_exporter

Prometheus exporter for Starlette and FastAPI.

The middleware collects basic metrics:

• 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.

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
...

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