Tutorial / FastAPI
Warning
[WIP tutorial]
The library offers a middleware that can be added to a FastAPI project to automatically get some metrics making it dead simple to get useful information at a low effort cost.
The middleware
The PytheusMiddlewareASGI when added to the project will collect three metrics:
http_request_duration_seconds: the duration of the http requesthttp_request_size_bytes: size in bytes of the requesthttp_response_size_bytes: size in bytes of the response
These will have three labels: method, path & status_code allowing for a lot of flexibility on observing your system. For example seeing the duration of GET requests to the /api path with a status_code of 200.
Note
http_request_size_bytes for now depends on the availability of the Content-Length header in the request.
Using the middleware
In the file where you are creating your FastAPI application import and add the middleware:
from fastapi import FastAPI
from pytheus.middleware import PytheusMiddlewareASGI
app = FastAPI()
app.add_middleware(PytheusMiddlewareASGI)
that will take care of collecting the metrics!
Now, we just need to decide where to expose the metrics, this is usually a /metrics endpoint:
from fastapi.responses import PlainTextResponse
from pytheus.exposition import generate_metrics
@app.get('/metrics', response_class=PlainTextResponse)
async def pytheus_metrics():
return generate_metrics()
That's it!
If you visit the /metrics endpoint twice you will able to see metrics for that request:
# HELP http_request_duration_seconds duration of the http request
# TYPE http_request_duration_seconds histogram
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="0.005"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="0.01"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="0.025"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="0.05"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="0.1"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="0.25"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="0.5"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="1"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="2.5"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="5"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="10"} 1.0
http_request_duration_seconds_bucket{method="GET",route="/metrics",status_code="200",le="+Inf"} 1.0
http_request_duration_seconds_sum{method="GET",route="/metrics",status_code="200"} 0.0014027919969521463
http_request_duration_seconds_count{method="GET",route="/metrics",status_code="200"} 1.0
# HELP http_request_size_bytes http request size
# TYPE http_request_size_bytes histogram
# HELP http_response_size_bytes http response size
# TYPE http_response_size_bytes histogram
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="10.0"} 0.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="100.0"} 0.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="1000.0"} 1.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="10000.0"} 1.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="100000.0"} 1.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="1000000.0"} 1.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="10000000.0"} 1.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="100000000.0"} 1.0
http_response_size_bytes_bucket{method="GET",route="/metrics",status_code="200",le="+Inf"} 1.0
http_response_size_bytes_sum{method="GET",route="/metrics",status_code="200"} 296.0
http_response_size_bytes_count{method="GET",route="/metrics",status_code="200"} 1.0
Note
You will need to hit /metrics twice because the first time on a fresh start you won't have metrics. On the second request you will see metrics from the previous request.