Logging Best Practices

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