Pino (Structured Logging)

Overview

Pino is the fastest JSON logger for Node.js. It outputs structured logs that integrate with observability platforms (Datadog, ELK, Splunk, CloudWatch).

Version: v9.x (2024-2025)
Performance: ~5x faster than Winston, ~10x faster than Bunyan

Key Benefit: Structured JSON logs → easy parsing, filtering, and alerting in production.

When to Use This Skill

✅ Use Pino when:

• Building production APIs
• Need structured JSON logs
• Integrating with observability platforms
• Require request tracing (correlation IDs)
• Must redact sensitive data (passwords, tokens)

❌ Skip Pino when:

• Simple scripts or CLI tools
• Early prototyping (console.log is fine)
• Client-side JavaScript

---

Quick Start

Installation

npm install pino pino-pretty
npm install -D @types/pino

Basic Configuration

// src/lib/logger.ts
import pino from 'pino';

const isDev = process.env.NODE_ENV === 'development';

export const logger = pino({
  level: process.env.LOG_LEVEL || (isDev ? 'debug' : 'info'),
  
  // Pretty print in development
  transport: isDev ? {
    target: 'pino-pretty',
    options: {
      colorize: true,
      translateTime: 'SYS:standard',
      ignore: 'pid,hostname',
    },
  } : undefined,
  
  // Redact sensitive fields
  redact: {
    paths: [
      'password',
      'token',
      'authorization',
      'cookie',
      '*.password',
      '*.token',
      'req.headers.authorization',
    ],
    censor: '[REDACTED]',
  },
  
  // Add base context to all logs
  base: {
    service: process.env.SERVICE_NAME || 'api',
    env: process.env.NODE_ENV,
    version: process.env.APP_VERSION,
  },
});

export default logger;

---

Log Levels

// In order of severity (lowest to highest)
logger.trace('Detailed debugging');     // level 10
logger.debug('Debug information');      // level 20
logger.info('Normal operation');        // level 30
logger.warn('Warning condition');       // level 40
logger.error('Error occurred');         // level 50
logger.fatal('App is crashing');        // level 60

Level Configuration

// Set via environment
LOG_LEVEL=debug npm start

// Or in code
const logger = pino({ level: 'debug' });

---

Structured Logging

Log Objects, Not Strings

// ❌ Avoid string interpolation
logger.info(`User ${userId} logged in from ${ip}`);

// ✅ Use structured objects
logger.info({ userId, ip, action: 'login' }, 'User logged in');

Output (JSON)

{
  "level": 30,
  "time": 1702300800000,
  "service": "api",
  "userId": "user_123",
  "ip": "192.168.1.1",
  "action": "login",
  "msg": "User logged in"
}

---

Child Loggers (Context)

Request Context

// Create child logger with request context
const requestLogger = logger.child({
  requestId: 'req_abc123',
  userId: 'user_456',
});

// All logs include context automatically
requestLogger.info('Processing request');
requestLogger.info({ orderId: 'order_789' }, 'Order created');

Output

{
  "requestId": "req_abc123",
  "userId": "user_456",
  "msg": "Processing request"
}
{
  "requestId": "req_abc123",
  "userId": "user_456",
  "orderId": "order_789",
  "msg": "Order created"
}

---

Express Request Logging

Middleware

// src/middleware/request-logger.ts
import { randomUUID } from 'crypto';
import { Request, Response, NextFunction } from 'express';
import { logger } from '../lib/logger';

// Extend Express Request type
declare global {
  namespace Express {
    interface Request {
      log: typeof logger;
      requestId: string;
    }
  }
}

export function requestLogger(req: Request, res: Response, next: NextFunction) {
  const requestId = (req.headers['x-request-id'] as string) || randomUUID();
  const start = Date.now();

  // Create child logger with request context
  const childLogger = logger.child({
    requestId,
    method: req.method,
    path: req.path,
    userAgent: req.headers['user-agent'],
  });

  // Attach to request for use in handlers
  req.log = childLogger;
  req.requestId = requestId;

  // Set response header for tracing
  res.setHeader('x-request-id', requestId);

  // Log request start
  childLogger.info('Request started');

  // Log request completion
  res.on('finish', () => {
    childLogger.info({
      statusCode: res.statusCode,
      duration: Date.now() - start,
    }, 'Request completed');
  });

  next();
}

Usage in Express

// src/app.ts
import express from 'express';
import { requestLogger } from './middleware/request-logger';

const app = express();
app.use(requestLogger);

app.get('/users/:id', async (req, res) => {
  req.log.info({ userId: req.params.id }, 'Fetching user');
  
  try {
    const user = await getUser(req.params.id);
    req.log.debug({ user }, 'User found');
    res.json(user);
  } catch (error) {
    req.log.error({ error }, 'Failed to fetch user');
    res.status(500).json({ error: 'Internal error' });
  }
});

---

tRPC Logging Middleware

// src/server/middleware/logging.ts
import { middleware } from '../trpc';
import { logger } from '@/lib/logger';

export const loggerMiddleware = middleware(async ({ path, type, next, ctx }) => {
  const start = Date.now();
  const log = ctx.log || logger;
  
  log.debug({ path, type }, 'tRPC procedure started');

  try {
    const result = await next();
    
    log.info({
      path,
      type,
      duration: Date.now() - start,
    }, 'tRPC procedure completed');
    
    return result;
  } catch (error) {
    log.error({
      path,
      type,
      duration: Date.now() - start,
      error,
    }, 'tRPC procedure failed');
    
    throw error;
  }
});

// Apply to all procedures
export const loggedProcedure = publicProcedure.use(loggerMiddleware);

---

Error Logging

With Stack Traces

try {
  await riskyOperation();
} catch (error) {
  // Pino serializes Error objects automatically
  logger.error({ err: error }, 'Operation failed');
}

Custom Error Serializer

const logger = pino({
  serializers: {
    err: pino.stdSerializers.err,  // Default error serializer
    error: (error) => ({
      type: error.constructor.name,
      message: error.message,
      stack: error.stack,
      code: error.code,
      // Add custom fields
      ...(error.details && { details: error.details }),
    }),
  },
});

---

Sensitive Data Redaction

Configuration

const logger = pino({
  redact: {
    paths: [
      'password',
      'secret',
      'token',
      'apiKey',
      'authorization',
      'cookie',
      'creditCard',
      '*.password',           // Nested fields
      '*.secret',
      'req.headers.cookie',
      'req.headers.authorization',
      'user.email',           // PII
    ],
    censor: '[REDACTED]',
    remove: false,            // Keep key, redact value
  },
});

Output

{
  "user": {
    "id": "123",
    "email": "[REDACTED]",
    "password": "[REDACTED]"
  }
}

---

Production Configuration

// src/lib/logger.ts
import pino from 'pino';

const isProduction = process.env.NODE_ENV === 'production';

export const logger = pino({
  level: process.env.LOG_LEVEL || 'info',
  
  // No transport in production (JSON to stdout)
  transport: isProduction ? undefined : {
    target: 'pino-pretty',
  },
  
  // Faster serialization in production
  formatters: {
    level: (label) => ({ level: label }),
  },
  
  // ISO timestamp
  timestamp: pino.stdTimeFunctions.isoTime,
  
  // Redaction
  redact: ['password', 'token', '*.password'],
  
  // Base context
  base: {
    service: process.env.SERVICE_NAME,
    version: process.env.APP_VERSION,
    env: process.env.NODE_ENV,
  },
});

---

Rules

Do ✅

• Use structured objects, not string interpolation
• Create child loggers for request context
• Redact sensitive data (passwords, tokens, PII)
• Include correlation IDs for tracing
• Use appropriate log levels
• Log errors with { err: error }

Avoid ❌

• console.log() in production code
• Logging sensitive data (passwords, tokens)
• String interpolation for structured data
• Excessive debug logging in production
• Blocking I/O in log transports

---

Log Level Guidelines

| Level | Use Case | Production | |-------|----------|------------| | trace | Very detailed debugging | Off | | debug | Development debugging | Off | | info | Normal operations | On | | warn | Potential issues | On | | error | Errors (handled) | On | | fatal | App crashing | On |

---

Troubleshooting

"Logs not appearing":
  → Check LOG_LEVEL environment variable
  → Verify level: logger.level returns current level
  → Debug level is often disabled in production

"pino-pretty not working":
  → Only use in development
  → Check transport configuration
  → npm install pino-pretty

"Sensitive data in logs":
  → Add paths to redact array
  → Use wildcards: '*.password'
  → Verify with test logs

"Performance issues":
  → Remove pino-pretty in production
  → Reduce log level
  → Check for sync logging (avoid)

---

Integration with Observability

Datadog

// Datadog expects JSON logs to stdout
const logger = pino({
  formatters: {
    level: (label) => ({ level: label }),
  },
  // Datadog trace correlation
  mixin: () => ({
    dd: {
      trace_id: getCurrentTraceId(),
      span_id: getCurrentSpanId(),
    },
  }),
});

ELK Stack

// Elasticsearch-friendly format
const logger = pino({
  timestamp: pino.stdTimeFunctions.isoTime,
  formatters: {
    level: (label) => ({ level: label }),
  },
});

---

File Structure

src/
├── lib/
│   └── logger.ts           # Logger configuration
├── middleware/
│   └── request-logger.ts   # Express middleware
└── server/
    └── middleware/
        └── logging.ts      # tRPC middleware

References

• https://getpino.io — Official documentation
• https://github.com/pinojs/pino — GitHub
• https://github.com/pinojs/pino-pretty — Pretty printing