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164"""Metrics middleware for FastAPI with OpenTelemetry and Prometheus.
This module provides automatic instrumentation for HTTP requests and
custom business metrics using OpenTelemetry and Prometheus.
Metrics exported on port 8001 (configurable via METRICS_PORT env var):
- HTTP request duration (histogram)
- HTTP request count by endpoint (counter)
- HTTP error rate by status code (counter)
- Active requests (gauge)
"""
import logging
from collections.abc import Awaitable, Callable
from fastapi import FastAPI, Request, Response
from prometheus_client import (
REGISTRY,
Counter,
Gauge,
Histogram,
generate_latest,
)
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.routing import Match
from ..config import settings
logger = logging.getLogger(__name__)
# Prometheus Metrics
http_requests_total = Counter(
"http_requests_total",
"Total HTTP requests",
["method", "endpoint", "status"],
)
http_request_duration_seconds = Histogram(
"http_request_duration_seconds",
"HTTP request duration in seconds",
["method", "endpoint"],
buckets=[0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0],
)
http_requests_in_progress = Gauge(
"http_requests_in_progress",
"Number of HTTP requests currently being processed",
["method", "endpoint"],
)
class MetricsMiddleware(BaseHTTPMiddleware):
"""Middleware to collect HTTP metrics."""
async def dispatch(
self, request: Request, call_next: Callable[[Request], Awaitable[Response]]
) -> Response:
"""Process request and collect metrics.
Args:
request: FastAPI request object
call_next: Next middleware/handler in chain
Returns:
Response from downstream handler
"""
# Skip metrics endpoint itself
if request.url.path == "/metrics":
return await call_next(request)
method = request.method
# Get endpoint pattern (e.g., /api/documents/{job_id}/status)
endpoint = self._get_endpoint_pattern(request)
# Track in-progress requests
http_requests_in_progress.labels(method=method, endpoint=endpoint).inc()
try:
# Time the request
with http_request_duration_seconds.labels(
method=method, endpoint=endpoint
).time():
response = await call_next(request)
# Record request
http_requests_total.labels(
method=method,
endpoint=endpoint,
status=response.status_code,
).inc()
return response
except Exception:
# Record error
http_requests_total.labels(
method=method,
endpoint=endpoint,
status=500,
).inc()
raise
finally:
# Decrement in-progress counter
http_requests_in_progress.labels(method=method, endpoint=endpoint).dec()
def _get_endpoint_pattern(self, request: Request) -> str:
"""Get endpoint pattern from request (e.g., /api/documents/{job_id}).
Args:
request: FastAPI request object
Returns:
Endpoint pattern string (or path if no pattern found)
"""
try:
for route in request.app.routes:
match, _ = route.matches(request.scope)
if match == Match.FULL:
return route.path # type: ignore[no-any-return]
# Fallback to raw path if no route matches
return request.url.path
except Exception as e:
logger.warning(f"Failed to get endpoint pattern: {e}")
return request.url.path
def setup_metrics(app: FastAPI) -> None:
"""Set up metrics collection for FastAPI application.
This function:
1. Registers the metrics middleware
2. Adds a /metrics endpoint for Prometheus scraping
Args:
app: FastAPI application instance
"""
if not settings.enable_metrics:
logger.info("Metrics collection disabled")
return
logger.info(f"Setting up metrics on port {settings.metrics_port}")
# Add metrics middleware
app.add_middleware(MetricsMiddleware)
# Add metrics endpoint
@app.get("/metrics", include_in_schema=False)
async def metrics() -> Response:
"""Prometheus metrics endpoint.
Returns:
Response with Prometheus format metrics
"""
return Response(
content=generate_latest(REGISTRY),
media_type="text/plain; version=0.0.4",
)
logger.info("Metrics collection enabled at /metrics")