Bits of .NET

📝 Log to stdout/stderr, Not Files

Log files inside container fill disk. Container restarts lose logs. Docker captures stdout/stderr. Use docker logs.

✅ Good vs Bad

// ❌ BAD: Writing to file
File.WriteAllText("/app/logs/app.log", message);

// ✅ GOOD: Console output
Console.WriteLine(message);

// ❌ BAD: Log4Net to file
// ✅ GOOD: Serilog to Console

// Docker command to see logs
docker logs container_name
docker logs -f container_name  # follow
docker logs --tail 100 container_name
docker logs --since 2024-01-01 container_name

🎯 JSON Logging

// Structured logging (JSON)
Console.WriteLine(JsonSerializer.Serialize(new {
    level = "Information",
    message = "User logged in",
    userId = 123,
    timestamp = DateTime.UtcNow
}));

// Docker parses JSON logs automatically
docker logs --details container_name

// Log drivers
docker run --log-driver json-file --log-opt max-size=10m --log-opt max-file=3
docker run --log-driver fluentd --log-opt fluentd-address=localhost:24224

💡 Log Management

• Set log rotation: –log-opt max-size=10m –log-opt max-file=3
• Use Fluentd, Logstash, or Loki for aggregation
• ELK stack (Elasticsearch, Logstash, Kibana) for centralized logging
• Never store logs inside container (they disappear on restart)