Logging best practices

Logging Best Practices

Table of Contents

• Overview
• When to Use
• Quick Start
• Reference Guides
• 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:

Guide	Contents
Log Levels	Log Levels
Structured Logging (JSON)	Structured Logging (JSON)
Contextual Logging	Contextual Logging
PII and Sensitive Data Handling	PII and Sensitive Data Handling
Performance Logging	Performance Logging
Centralized Logging	Centralized Logging
Distributed Tracing	Distributed Tracing
Log Sampling (High-Volume Services)	Log Sampling (High-Volume Services)

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