Application Logging

Table of Contents

• Overview
• When to Use
• Quick Start
• Reference Guides
• Best Practices

Overview

Implement comprehensive structured logging with proper levels, context, and centralized aggregation for effective debugging and monitoring.

When to Use

• Application debugging
• Audit trail creation
• Performance analysis
• Compliance requirements
• Centralized log aggregation

Quick Start

Minimal working example:

// logger.js
const winston = require("winston");

const logFormat = winston.format.combine(
  winston.format.timestamp({ format: "YYYY-MM-DD HH:mm:ss" }),
  winston.format.errors({ stack: true }),
  winston.format.json(),
);

const logger = winston.createLogger({
  level: process.env.LOG_LEVEL || "info",
  format: logFormat,
  defaultMeta: {
    service: "api-service",
    environment: process.env.NODE_ENV || "development",
  },
  transports: [
    new winston.transports.Console({
      format: winston.format.combine(
        winston.format.colorize(),
        winston.format.simple(),
      ),
    }),
    new winston.transports.File({
      filename: "logs/error.log",
// ... (see reference guides for full implementation)

Reference Guides

Detailed implementations in the references/ directory:

Guide	Contents
Node.js Structured Logging with Winston	Node.js Structured Logging with Winston
Express HTTP Request Logging	Express HTTP Request Logging
Python Structured Logging	Python Structured Logging
Flask Integration	Flask Integration
ELK Stack Setup	ELK Stack Setup
Logstash Configuration	Logstash Configuration

Best Practices

✅ DO

• Use structured JSON logging
• Include request IDs for tracing
• Log at appropriate levels
• Add context to error logs
• Implement log rotation
• Use timestamps consistently
• Aggregate logs centrally
• Filter sensitive data

❌ DON'T

• Log passwords or secrets
• Log at INFO for every operation
• Use unstructured messages
• Ignore log storage limits
• Skip context information
• Log to stdout in production
• Create unbounded log files