如何为FastAPI路由的OpenTelemetry Span添加用户ID属性？

No problem at all! Since you've already instrumented your FastAPI app with OpenTelemetry, adding the user ID as a custom attribute (tag) to your request spans is straightforward. Here's how to modify your code:

Updated main.py Code #

from typing import Dict
import fastapi
from opentelemetry import trace
from opentelemetry.sdk.trace.export import (
    ConsoleSpanExporter,
    SimpleExportSpanProcessor,
)
from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
from opentelemetry.sdk.trace import TracerProvider

trace.set_tracer_provider(TracerProvider())
trace.get_tracer_provider().add_span_processor(
    SimpleExportSpanProcessor(ConsoleSpanExporter())
)

app = fastapi.FastAPI()

@app.get("/user/{id}")
async def get_user(id: int) -> Dict[str, str]:
    """Test endpoint."""
    # Get the currently active span for this request
    current_span = trace.get_current_span()
    # Add the user ID as a custom attribute (tag)
    current_span.set_attribute("user.id", id)
    return {"message": "hello user!"}

FastAPIInstrumentor.instrument_app(app)

How This Works #

• trace.get_current_span() fetches the active span that's automatically created by the FastAPI OpenTelemetry instrumentation for each incoming request.
• set_attribute(key, value) adds your custom tag to the span. You can use any meaningful key name (following OpenTelemetry naming conventions, using dots for hierarchy is a good practice like user.id).

Verify the Result #

Run your app with uvicorn main:app --reload, then send a request to http://localhost:8000/user/123. Check your console output—you'll see the attributes section of the span now includes "user.id": 123.

If you need to add attributes to spans in multiple endpoints, you could even wrap this logic into a dependency to keep your code DRY!

内容的提问来源于stack exchange，提问作者louis_guitton