application-logging

SKILL.md

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

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