Logging Best Practices for Go Microservices

Use structured JSON logging with context, correlation IDs, and severity levels to ensure traceability across microservices. Implement this pattern by initializing a logger with the log/slog package and passing context through your handlers.

import (
	"context"
	"log/slog"
	"os"
)

func init() {
	slog.SetDefault(slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
		Level: slog.LevelInfo,
	})))
}

func handleRequest(ctx context.Context) {
	logger := slog.With("trace_id", getTraceID(ctx))
	logger.Info("request started")
	// ... business logic
	logger.Info("request completed")
}

1. Initialize the logger with slog.NewJSONHandler to output structured JSON to os.Stdout.
2. Create a context-aware logger using slog.WithContext to attach request-specific data like trace IDs.
3. Log events at appropriate levels (Info, Warn, Error) including the trace ID for distributed tracing.
4. Ensure all service-to-service calls propagate the trace ID in headers to maintain the correlation chain.

Logging in Go microservices means recording what your code does in a format that machines can easily read and search. You should include a unique ID for each request so you can follow it as it jumps between different services. Think of it like a passport stamp that travels with a user's request, letting you see exactly where it went and what happened at each stop.