Go Observability

Observability is not optional for production services. Every service must produce structured logs, expose metrics, and propagate trace context. Use the stdlib log/slog for logging and OpenTelemetry for tracing and metrics.

1. Structured Logging with slog

Use log/slog (Go 1.21+) as the standard logging package:

// ✅ Good — structured, leveled logging
logger := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
    Level: slog.LevelInfo,
}))

logger.Info("user created",
    slog.String("user_id", user.ID),
    slog.String("email", user.Email),