Golang Logging

Golang Logging Standards

Priority: P1 (HIGH)

Principles

• Structured Logging: Use JSON or structured text. Readable by machines and humans.
• Leveled Logging: Debug, Info, Warn, Error.
• Contextual: Include correlation IDs (TraceID, RequestID) in logs.
• No log.Fatal: Avoid terminating app inside libraries. Return error instead. Only main should exit.

Libraries

• log/slog (Recommended): Stdlib since Go 1.21. Fast, structured, zero-dep.
• Zap (uber-go/zap): High performance, good if pre-1.21 or extreme throughput needed.
• Zerolog: Zero allocation, fast JSON logger.

Workflow: Set Up Structured Logging with slog

1. Create JSON handler at startup in main()
2. Optionally wrap in middleware to inject request-scoped attributes
3. Use slog.With() to add correlation IDs per request
4. Pass logger via context or dependency injection

See slog setup and usage examples

References

• Slog Patterns

Anti-Patterns

• No fmt.Println in production: Use slog or zap for structured, leveled logging.
• No log.Fatal in libraries: Return errors; only main() should call os.Exit.
• No unstructured log strings: Include correlation IDs and structured fields via slog.Attr.