Logging Best Practices

Table of Contents

• [Overview](#overview)

• [When to Use](#when-to-use)

• [Quick Start](#quick-start)

• [Reference Guides](#reference-guides)

• [Best Practices](#best-practices)

Overview

Comprehensive guide to implementing structured, secure, and performant logging across applications. Covers log levels, structured logging formats, contextual information, PII protection, and centralized logging systems.

When to Use

• Setting up application logging infrastructure

• Implementing structured logging

• Configuring log levels for different environments

• Managing sensitive data in logs

• Setting up centralized logging

• Implementing distributed tracing

• Debugging production issues

• Compliance with logging regulations

Quick Start

Minimal working example:

// logger.ts

enum LogLevel {

  DEBUG = 0, // Detailed information for debugging

  INFO = 1, // General informational messages

  WARN = 2, // Warning messages, potentially harmful

  ERROR = 3, // Error messages, application can continue

  FATAL = 4, // Critical errors, application must stop

}

class Logger {

  constructor(private minLevel: LogLevel = LogLevel.INFO) {}

  debug(message: string, context?: object) {

    if (this.minLevel <= LogLevel.DEBUG) {

      this.log(LogLevel.DEBUG, message, context);

    }

  }

  info(message: string, context?: object) {

    if (this.minLevel <= LogLevel.INFO) {

      this.log(LogLevel.INFO, message, context);

    }

  }

  warn(message: string, context?: object) {

// ... (see reference guides for full implementation)

Reference Guides

Detailed implementations in the references/ directory:

Best Practices

✅ DO

• Use structured logging (JSON) in production

• Include correlation/request IDs in all logs

• Log at appropriate levels (don't overuse DEBUG)

• Redact sensitive data (PII, passwords, tokens)

• Include context (userId, requestId, etc.)

• Log errors with full stack traces

• Use centralized logging in distributed systems

• Set up log rotation to manage disk space

• Monitor log volume and costs

• Use async logging for performance

• Include timestamps in ISO 8601 format

• Log business events (user actions, transactions)

• Set up alerts for error patterns

❌ DON'T

• Log passwords, tokens, or sensitive data

• Use console.log in production

• Log at DEBUG level in production by default

• Log inside tight loops (use sampling)

• Include PII without anonymization

• Ignore log rotation (disk will fill up)

• Use synchronous logging in hot paths

• Log to multiple transports without need

• Forget to include error stack traces

• Log binary data or large objects

• Use string concatenation (use structured fields)

• Log every single request in high-volume APIs