Logging Like a Pro

Why Logging Matters

Effective logging is essential for debugging, monitoring, and auditing. It helps uncover issues in production and ensures traceability of actions in your applications.

What Makes a Good Log Message

// Good
                      _log.Info("User login successful: userId=1234");
                      
                      // Bad
                      _log.Info("Something happened");
                        

Log Levels Explained

Level	Purpose	When to Use
DEBUG	Internal dev info	Tracing logic, flow
INFO	High-level events	User login, request received
WARN	Unexpected but non-breaking	Retry attempt, fallback used
ERROR	Application failure	DB not reachable, exception thrown
FATAL	System critical failure	Service crash

Structured vs Unstructured Logging

// Structured
                      {
                        "timestamp": "2025-06-09T08:00:00Z",
                        "level": "INFO",
                        "message": "User logged in",
                        "userId": "1234"
                      }
                      
                      // Unstructured
                      User logged in successfully with ID 1234
                        

Logging in C# with Serilog

Log.Logger = new LoggerConfiguration()
                          .MinimumLevel.Debug()
                          .WriteTo.Console()
                          .WriteTo.File("logs/log.txt", rollingInterval: RollingInterval.Day)
                          .CreateLogger();
                      
                      Log.Information("Application Started");
                        

Logging in Python

import logging
                      
                      logging.basicConfig(level=logging.INFO,
                          format='%(asctime)s - %(levelname)s - %(message)s')
                      
                      logging.info("Service started")
                        

Real-World Logging Examples

// C# Bad
                      _log.Error("Exception occurred");
                      
                      // C# Good
                      _log.Error(ex, "Payment processing failed for OrderId={OrderId}", orderId);
                        

# Python Bad
                      logging.warning("Something is wrong")
                      
                      # Python Good
                      logging.warning("Payment delay detected for user_id=%s", user_id)
                        

Anti-Patterns to Avoid

• ❌ Logging passwords, tokens, or PII
• ❌ Logging stack traces without context
• ❌ Overusing INFO/ERROR for all logs
• ❌ Ignoring structured logs in favor of raw text

Stay tuned for quiz and downloadable guide!