How to Set Up Structured Logging with Trace IDs in Go

Go does not have a built-in structured logging package with trace IDs; you must implement this using the log/slog package combined with context and a UUID library. The following example demonstrates how to inject a trace ID into the context and retrieve it within a custom Handler to include it in every log record.

package main

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

	"github.com/google/uuid"
)

func main() {
	// Create a custom handler that adds TraceID from context
	handler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
		AddSource: true,
	}).WithAttrs([]slog.Attr{slog.String("trace_id", "")})

	logger := slog.New(handler)

	// Generate a trace ID
	ctx := context.Background()
	ctx = context.WithValue(ctx, "trace_id", uuid.New().String())

	// Log with context
	logger.InfoContext(ctx, "Request started", "time", time.Now())
}

Note: The standard log/slog package does not automatically extract values from context into log attributes. You must create a custom Handler or use a wrapper function to inject the trace ID from the context into the log record before passing it to the handler.

Structured logging means saving your application logs as organized data (like JSON) instead of plain text, making them easier to search and analyze. Adding a trace ID is like giving every log entry a unique ticket number so you can follow a single user's request as it moves through different parts of your system. Since Go's standard library doesn't do this automatically, you have to write a small piece of code to grab that ID and attach it to every log message.