Fastify

Setup

instrumentation.ts

import { init } from 'autotel';

init({
  service: 'my-fastify-api',
  autoInstrumentations: ['http', 'fastify'],
  endpoint: process.env.OTLP_ENDPOINT,
});

Run with:

tsx --import ./instrumentation.ts src/index.ts

Tracing Route Handlers

import Fastify from 'fastify';
import { trace, type TraceContext } from 'autotel';

const app = Fastify({ logger: true });

const fetchUser = trace((ctx: TraceContext) => async (userId: string) => {
  ctx.setAttribute('db.userId', userId);
  await new Promise((resolve) => setTimeout(resolve, 50));
  return { id: userId, name: `User ${userId}` };
});

app.get('/users/:userId', async (request, reply) => {
  const { userId } = request.params;
  try {
    return await fetchUser(userId);
  } catch {
    reply.code(500);
    return { error: 'Failed to fetch user' };
  }
});

app.get('/error', async () => {
  throw new Error('Test error');
});

await app.listen({ port: 3000 });

What Gets Traced

With autoInstrumentations: ['http', 'fastify']:

• HTTP server spans — automatic per-request spans
• Fastify lifecycle — hook and handler execution time
• Your trace() calls — business logic spans as children

Examples

• example-fastify — Fastify with HTTP/Fastify auto-instrumentation and manual trace().