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FastAPI LLM app monitoring best practices

Q: FastAPI LLM app monitoring best practices

Use Prometheus and Grafana for metrics collection and visualization, integrate structured logging with correlation IDs, implement health check endpoints, and use error tracking tools like Sentry to monitor your FastAPI LLM app effectively. Combine these with request tracing and rate limiting for robust observability and reliability.

Quick answer

Use Prometheus and Grafana for metrics collection and visualization, integrate structured logging with correlation IDs, implement health check endpoints, and use error tracking tools like Sentry to monitor your FastAPI LLM app effectively. Combine these with request tracing and rate limiting for robust observability and reliability.

PREREQUISITES

Python 3.8+
FastAPI
pip install fastapi uvicorn prometheus-client sentry-sdk

Setup monitoring tools

Install and configure essential monitoring tools such as prometheus-client for metrics, sentry-sdk for error tracking, and set up structured logging in your FastAPI app.

bash

pip install fastapi uvicorn prometheus-client sentry-sdk

Step by step example

This example shows how to add Prometheus metrics, Sentry error tracking, structured logging, and a health check endpoint to a FastAPI app serving an LLM.

python

import os
import logging
from fastapi import FastAPI, Request, Response
from prometheus_client import Counter, generate_latest, CONTENT_TYPE_LATEST
from prometheus_client import start_http_server
import sentry_sdk
from sentry_sdk.integrations.asgi import SentryAsgiMiddleware

# Initialize Sentry for error tracking
sentry_sdk.init(dsn=os.environ.get("SENTRY_DSN"))

app = FastAPI()
app.add_middleware(SentryAsgiMiddleware)

# Setup Prometheus metrics
REQUEST_COUNT = Counter('fastapi_requests_total', 'Total HTTP requests', ['method', 'endpoint', 'http_status'])

# Configure logging
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(levelname)s - %(message)s'
)
logger = logging.getLogger(__name__)

@app.middleware("http")
async def metrics_middleware(request: Request, call_next):
    response = await call_next(request)
    REQUEST_COUNT.labels(request.method, request.url.path, response.status_code).inc()
    logger.info(f"{request.method} {request.url.path} {response.status_code}")
    return response

@app.get("/metrics")
async def metrics():
    return Response(generate_latest(), media_type=CONTENT_TYPE_LATEST)

@app.get("/health")
async def health_check():
    return {"status": "healthy"}

@app.post("/llm")
async def llm_endpoint(request: Request):
    data = await request.json()
    prompt = data.get("prompt", "")
    logger.info(f"Received prompt: {prompt}")
    # Simulate LLM response
    if not prompt:
        logger.error("Empty prompt received")
        return {"error": "Prompt is required"}
    response_text = f"Echo: {prompt}"
    return {"response": response_text}

if __name__ == "__main__":
    # Start Prometheus metrics server on a separate port
    start_http_server(8001)
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=8000)

Common variations

Use async endpoints for better concurrency with FastAPI.
Integrate OpenTelemetry for distributed tracing.
Switch to different LLM models by changing your inference backend.
Use logging libraries like structlog for enhanced structured logs.

Troubleshooting tips

If metrics do not appear in Prometheus, verify the /metrics endpoint is reachable and prometheus-client server is running.
For missing Sentry errors, check your SENTRY_DSN environment variable and network connectivity.
Ensure logging output is not suppressed by your environment or container settings.

✅

Key Takeaways

Use Prometheus and Grafana for real-time metrics and visualization in FastAPI LLM apps.
Integrate Sentry for robust error tracking and alerting.
Implement structured logging with correlation IDs for traceability.
Add health check endpoints to monitor app availability.
Consider distributed tracing and rate limiting for production-grade observability.

Verified 2026-04 · gpt-4o, claude-3-5-sonnet-20241022

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