Logging with Pino

Configure Pino through Fastify for structured JSON logs with request context and production-ready performance.

Recipe

Quick-reference recipe card - copy-paste ready.

import Fastify from "fastify";
 
const app = Fastify({
  logger: {
    level: process.env.LOG_LEVEL ?? "info",
    redact: ["req.headers.authorization", "req.body.password"],
    serializers: {
      req(req) {
        return { method: req.method, url: req.url, id: req.id };
      },
    },
  },
});
 
app.get("/users", async (req) => {
  req.log.info({ action: "list_users" });
  return [];
});

When to reach for this: Every Fastify service. Pino is the default and the right choice for production JSON logging.

Working Example

import Fastify from "fastify";
 
const app = Fastify({
  logger: {
    level: "info",
    timestamp: () => `,"time":"${new Date().toISOString()}"`,
    redact: {
      paths: ["req.headers.authorization", "req.headers.cookie", "body.password"],
      censor: "[REDACTED]",
    },
  },
  genReqId: (req) => req.headers["x-request-id"] as string ?? crypto.randomUUID(),
  requestIdLogLabel: "requestId",
});
 
app.addHook("onRequest", async (req) => {
  req.log.info({ event: "request_start" });
});
 
app.addHook("onResponse", async (req, reply) => {
  req.log.info({
    event: "request_complete",
    statusCode: reply.statusCode,
    responseTime: reply.elapsedTime,
  });
});
 
app.get("/users/:id", async (req) => {
  req.log.info({ userId: req.params.id, action: "get_user" });
  return { id: (req.params as { id: string }).id };
});

What this demonstrates:

• Structured JSON logs with request ID propagation
• Redaction of sensitive headers and body fields
• Request lifecycle logging via hooks
• reply.elapsedTime for response timing

Deep Dive

How It Works

• Pino writes JSON lines to stdout (one log per line)
• req.log is a child logger bound to the request ID
• Pino is async: serializes in worker thread (minimal main-thread impact)
• Log aggregators (Datadog, Loki, CloudWatch) parse JSON lines natively

Log Levels

Development Pretty Print

const app = Fastify({
  logger: {
    transport: process.env.NODE_ENV === "development"
      ? { target: "pino-pretty", options: { colorize: true } }
      : undefined,
  },
});

Never use pino-pretty in production. It blocks the main thread.

Gotchas

• Logging full req.body - PII in log storage. Fix: redact paths; log only necessary fields.
• pino-pretty in production - kills throughput and blocks event loop. Fix: JSON to stdout only.
• Missing request ID - cannot correlate logs across services. Fix: genReqId from x-request-id header.
• console.log alongside Pino - unstructured logs mixed with JSON. Fix: ban console.log in lint rules.
• Logging inside tight loops - log volume explodes. Fix: sample or aggregate.
• Not logging error context - log.error(err) without err serializer loses stack. Fix: req.log.error({ err }, "message").

Alternatives

FAQs

Related

• Logging Basics - structured logging principles
• Request Correlation IDs - distributed tracing
• PII Redaction and Compliance - redaction rules
• Fastify Basics - logger configuration
• Fastify Best Practices - section checklist

Stack versions: This page was written for Node.js 24.18.0 (Active LTS), npm 10+, TypeScript 5.6+, Express 5, Fastify 5, and NestJS 11.