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
