Tie every line to its request

How to do it

At the edge, accept an incoming traceparent header only if it matches the W3C format, otherwise create a new random ID. Keep the ID in request context, add it to every log line, and return it in a response header. Pass it on every outgoing call. Show it on error pages, so support can find the exact lines.

Example

import { AsyncLocalStorage } from 'node:async_hooks';
import { randomUUID } from 'node:crypto';

const TRACEPARENT = /^00-([0-9a-f]{32})-[0-9a-f]{16}-[0-9a-f]{2}$/;
export const requestContext = new AsyncLocalStorage();

app.use((req, res, next) => {
  const requestId = TRACEPARENT.exec(req.get('traceparent') ?? '')?.[1] ?? randomUUID().replaceAll('-', '');
  res.set('X-Request-Id', requestId);
  requestContext.run({ requestId, log: log.child({ request_id: requestId }) }, next);
});

import re
import uuid
import structlog

TRACEPARENT = re.compile(r"^00-([0-9a-f]{32})-[0-9a-f]{16}-[0-9a-f]{2}$")

@app.middleware("http")
async def tag_request(request, call_next):
    match = TRACEPARENT.match(request.headers.get("traceparent", ""))
    request_id = match.group(1) if match else uuid.uuid4().hex
    structlog.contextvars.clear_contextvars()
    structlog.contextvars.bind_contextvars(request_id=request_id)
    response = await call_next(request)
    response.headers["X-Request-Id"] = request_id
    return response

How to check

Trigger an error on staging. The error page shows an ID, and searching the logs for it returns every line of that request, across services.