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Ustrukturyzowane logowanie z identyfikatorami korelacji

Generuj możliwe do odczytu maszynowego logi JSON i przekazuj identyfikatory korelacji przez kontekst asynchroniczny do śledzenia żądań

Ustrukturyzowane logowanie z identyfikatorami korelacji to bezpłatna lekcja Node.js Backend Development Bootcamp na CoddyKit. To lekcja 1 z 4. Możesz przeczytać całą lekcję poniżej za darmo — a potem ćwiczyć ją interaktywnie w przeglądarce z wbudowanym edytorem kodu i tutorem AI dostępnym 24/7. To część ścieżki edukacyjnej Node.js Backend Development Bootcamp, a Twój postęp synchronizuje się między webem a aplikacją CoddyKit. Kurs Node.js Backend Development Bootcamp zawiera 4 lekcji w sumie.

Części tej lekcji nie zostały jeszcze przetłumaczone i są wyświetlane po angielsku.

Why Structured Logging

In production, logs are read by machines before humans. A line like console.log('User ' + id + ' failed login') is a free-form string: to find it later you must write brittle regex and you cannot aggregate or filter reliably.

Structured logging emits each log as a JSON object with consistent fields. Log aggregators (Loki, Elasticsearch, Datadog, CloudWatch) index those fields so you can query level="error" AND userId=42 instantly.

  • Free-form: easy to write, painful to query.
  • Structured: one JSON object per line (NDJSON), trivially parseable.

A Minimal JSON Logger

The core idea is small: build a plain object, stamp it with a level and timestamp, and write one JSON string per line to stdout. The runtime or container collects stdout and ships it to your aggregator.

Each log is a single line of valid JSON. This format is called NDJSON (newline-delimited JSON) and every modern log backend understands it.

function log(level, message, fields = {}) {
  const entry = {
    level,
    time: new Date().toISOString(),
    message,
    ...fields,
  };
  process.stdout.write(JSON.stringify(entry) + '\n');
}

log('info', 'server started', { port: 3000 });
log('error', 'login failed', { userId: 42, reason: 'bad_password' });

Use a Real Logger: pino

Hand-rolling works for learning, but production apps use a battle-tested logger. pino is the de-facto choice for Node.js: it is extremely fast because it serializes JSON in a worker-friendly way and writes asynchronously.

  • logger.info(obj, msg) — the first arg is the object of fields, the second is the message string.
  • Levels: trace, debug, info, warn, error, fatal.
  • In production you pipe stdout to pino-pretty only in dev; raw JSON goes to prod.
const pino = require('pino');
const logger = pino({ level: 'info' });

logger.info({ port: 3000 }, 'server started');
logger.error({ userId: 42, reason: 'bad_password' }, 'login failed');

// Child loggers bind fields onto every subsequent log:
const reqLog = logger.child({ requestId: 'abc-123' });
reqLog.info('handling request');

The Problem: Tracing One Request

Under load, hundreds of requests interleave their logs. When user 42 reports an error, you need to see every log line that belongs to their request — across middleware, services, and database calls.

The solution is a correlation ID (also called request ID or trace ID): a unique identifier generated once per request and attached to every log emitted while handling that request.

  • Query correlationId="7f3a..." and the aggregator reconstructs the whole request timeline.
  • If the ID arrives in an incoming header, you can correlate logs across services.

Generating and Accepting the ID

At the edge of your system, read an incoming correlation header if a caller (gateway, upstream service) already set one; otherwise generate a fresh UUID. Always echo it back in the response so clients and proxies can record it too.

Standard header names are x-request-id or x-correlation-id. Reusing an inbound ID is what makes tracing work across service boundaries.

const { randomUUID } = require('crypto');

function correlationMiddleware(req, res, next) {
  const incoming = req.headers['x-correlation-id'];
  const correlationId = incoming || randomUUID();
  req.correlationId = correlationId;
  res.setHeader('x-correlation-id', correlationId);
  next();
}

module.exports = { correlationMiddleware };

The Naive Approach and Its Pain

The obvious move is to pass req.correlationId as an argument into every function and every log call. This works but does not scale: a deep call stack (controller → service → repository → helper) forces you to thread the ID through functions that otherwise have no reason to know about it.

This is prop drilling for the backend. You want the ID available implicitly to any code running during the request — without changing every function signature.

AsyncLocalStorage to the Rescue

Node.js ships AsyncLocalStorage (in the async_hooks module). It creates a store that stays bound to the current asynchronous execution context — surviving across await, callbacks, timers, and promises — without being shared between concurrent requests.

Think of it as request-scoped thread-local storage. You call als.run(store, callback) once per request; anywhere inside that callback (no matter how deep or how many awaits later) als.getStore() returns the same store.

const { AsyncLocalStorage } = require('async_hooks');
const als = new AsyncLocalStorage();

async function deep() {
  await new Promise((r) => setTimeout(r, 10));
  // Same store, even after awaits and timers:
  return als.getStore().correlationId;
}

async function main() {
  await als.run({ correlationId: 'req-1' }, async () => {
    console.log('inside:', await deep());
  });
  console.log('outside:', als.getStore());
}

main();

Wiring AsyncLocalStorage into the Request

Replace the naive middleware: instead of attaching the ID to req, run the rest of the request inside als.run() with the ID in the store. Now every line of code executed for this request — controllers, services, DB callbacks — can reach the ID via getStore().

Crucially, you must call next() inside the run callback so the downstream handlers inherit the context.

const { AsyncLocalStorage } = require('async_hooks');
const { randomUUID } = require('crypto');

const als = new AsyncLocalStorage();

function context() {
  return als.getStore() || {};
}

function correlationMiddleware(req, res, next) {
  const correlationId = req.headers['x-correlation-id'] || randomUUID();
  res.setHeader('x-correlation-id', correlationId);
  als.run({ correlationId }, () => next());
}

module.exports = { als, context, correlationMiddleware };

Auto-Injecting the ID into Every Log

The payoff: wrap your logger so it reads the correlation ID from AsyncLocalStorage automatically. Application code calls log.info('saved order') with no ID argument, yet every emitted line carries the right correlationId.

With pino you express this declaratively using the mixin option, which merges extra fields into every log record at write time.

const pino = require('pino');
const { als } = require('./context');

const logger = pino({
  level: 'info',
  mixin() {
    const store = als.getStore();
    return store ? { correlationId: store.correlationId } : {};
  },
});

// Anywhere deep in the request, no ID passed explicitly:
function saveOrder(order) {
  logger.info({ orderId: order.id }, 'order saved');
}

module.exports = { logger, saveOrder };

Propagating the ID to Downstream Calls

Correlation only spans services if you forward the ID on outbound requests. When your service calls another HTTP API, read the ID from context and set it as a header. The downstream service's middleware will reuse it, so both services' logs share one ID.

The same principle applies to message queues (put the ID in message metadata) and background jobs (store it on the job payload).

const { context } = require('./context');

async function callInventoryService(sku) {
  const { correlationId } = context();
  const res = await fetch('https://inventory.internal/check', {
    method: 'POST',
    headers: {
      'content-type': 'application/json',
      'x-correlation-id': correlationId,
    },
    body: JSON.stringify({ sku }),
  });
  return res.json();
}

module.exports = { callInventoryService };

Production Hygiene

A few rules keep your structured logs clean and safe:

  • Never log secrets or PII — passwords, tokens, full card numbers. Configure pino redact paths (e.g. ['req.headers.authorization', '*.password']).
  • Log at the right level — info for business events, warn for recoverable issues, error with the serialized error object for failures.
  • Keep field names stable — correlationId always means the same thing; dashboards and alerts depend on it.
  • One JSON object per line — do not pretty-print in production; it breaks NDJSON parsing.
const pino = require('pino');

const logger = pino({
  level: process.env.LOG_LEVEL || 'info',
  redact: ['req.headers.authorization', 'password', '*.password', 'creditCard'],
});

logger.info({ user: { id: 7, password: 'hunter2' } }, 'login');
// -> password is replaced with [Redacted] in the output

Quick Check

You need the correlation ID available to every function in a deep call stack during a request, without passing it as an argument and without leaking it between concurrent requests. What is the correct mechanism in Node.js?

Recap

You learned how to make logs both machine-parseable and traceable:

  • Structured logging emits one JSON object per line (NDJSON) so aggregators can index and query fields.
  • pino is the standard fast Node.js logger; the field object comes first, the message second.
  • A correlation ID is generated or reused from an inbound header once per request and echoed in the response.
  • AsyncLocalStorage threads that ID through the whole async call stack without changing function signatures, and isolates concurrent requests.
  • Pino's mixin auto-injects the ID into every log; forwarding it as an outbound header extends tracing across services.
  • Practice good hygiene: redact secrets, use correct levels, keep field names stable, never pretty-print in production.

Często zadawane pytania

Czy lekcja „Ustrukturyzowane logowanie z identyfikatorami korelacji” jest bezpłatna?

Tak — pełny tekst „Ustrukturyzowane logowanie z identyfikatorami korelacji” jest dostępny za darmo tutaj w sieci. Aby ćwiczyć ją interaktywnie (wbudowany edytor kodu i tutor AI dostępny 24/7) i odblokować resztę kursu Node.js Backend Development Bootcamp, przejdź na CoddyKit PRO. Kurs Node.js Backend Development Bootcamp zawiera 4 lekcji w sumie.

Co nauczysz się w „Ustrukturyzowane logowanie z identyfikatorami korelacji”?

Generuj możliwe do odczytu maszynowego logi JSON i przekazuj identyfikatory korelacji przez kontekst asynchroniczny do śledzenia żądań Ćwiczysz Node.js Backend Development Bootcamp z praktycznym kodem, który uruchamiasz bezpośrednio w przeglądarce, a tutor AI dostępny 24/7 odpowiada na Twoje pytania podczas pracy nad lekcją.

Czy potrzebuję doświadczenia, aby zacząć Node.js Backend Development Bootcamp?

Nie wymagamy żadnego doświadczenia. Node.js Backend Development Bootcamp w CoddyKit jest strukturyzowany dla początkujących i zaawansowanych użytkowników, więc możesz zacząć tutaj lub od początku i uczyć się w swoim tempie. To lekcja 1 z 4.

Ile czasu zajmuje lekcja „Ustrukturyzowane logowanie z identyfikatorami korelacji”?

Większość lekcji CoddyKit trwa około 5–10 minut. Każda lekcja to mały, interaktywny krok, dzięki czemu robisz systematyczne postępy i zawsze wracasz dokładnie do tego samego miejsca — na webie i w aplikacji.

Czy mogę pisać i uruchamiać kod w tej lekcji Node.js Backend Development Bootcamp?

Tak. Każda lekcja Node.js Backend Development Bootcamp zawiera wbudowany edytor kodu, więc piszesz i uruchamiasz prawdziwy kod bezpośrednio w przeglądarce i od razu otrzymujesz sprzężenie zwrotne od AI — bez konfiguracji na komputerze.

Wszystkie lekcje w tym kursie

  1. Ustrukturyzowane logowanie z identyfikatorami korelacji
  2. Śledzenie rozproszone za pomocą spanów OpenTelemetry
  3. Udostępnianie metryk aplikacji i metoda RED
  4. Propagacja kontekstu za pomocą AsyncLocalStorage
← Powrót do Node.js Backend Development Bootcamp