feat(cli): implement structured logging

Author: batovpasha

cmd/cli/main.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"log/slog"
 	"os"
 	"time"
 
@@ -14,6 +15,20 @@ import (
 	"github.com/batovpasha/aws-cw-log-sampler/internal/sample"
 )
 
+type contextHandler struct {
+	slog.Handler
+}
+type ctxKey string
+
+const traceIDKey ctxKey = "trace_id"
+
+func (h *contextHandler) Handle(ctx context.Context, r slog.Record) error {
+	if traceId, ok := ctx.Value(traceIDKey).(string); ok {
+		r.AddAttrs(slog.String(string(traceIDKey), traceId))
+	}
+	return h.Handler.Handle(ctx, r)
+}
+
 func main() {
 	fs := flag.CommandLine
 	flags := cli.RegisterCommonFlags(fs)
@@ -30,7 +45,12 @@ func main() {
 		os.Exit(1)
 	}
 
-	ctx := context.Background()
+	h := slog.NewJSONHandler(os.Stdout, nil)
+	logger := slog.New(&contextHandler{Handler: h})
+	slog.SetDefault(logger)
+	traceID := time.Now().UTC().Format(time.RFC3339)
+	ctx := context.WithValue(context.Background(), traceIDKey, traceID)
+
 	cfg, err := config.LoadDefaultConfig(ctx)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)

internal/cloudwatchlogs/cloudwatchlogs.go

@@ -41,7 +41,6 @@ Outer:
 			return nil, fmt.Errorf("describe log streams: %w", err)
 		}
 		if len(output.LogStreams) == 0 {
-			fmt.Println("no streams found in", logGroupName)
 			break
 		}
 

internal/sample/rand_log_streams.go

@@ -3,7 +3,7 @@ package sample
 import (
 	"context"
 	"fmt"
-	"log"
+	"log/slog"
 	"math/rand/v2"
 	"sync/atomic"
 	"time"
@@ -36,7 +36,7 @@ func SampleByRandLogStreams(
 		g.Go(func() error {
 			processed, err := processLogGroup(ctx, client, cutoff, srcGroup, dstGroup, randLogStreamsNumber)
 			if err != nil {
-				fmt.Printf("error processing log group %s: %v\n", srcGroup, err)
+				slog.WarnContext(ctx, "error processing log group", "log_group", srcGroup, "error", err)
 				return nil
 			}
 			processedLogStreams.Add(processed)
@@ -45,7 +45,7 @@ func SampleByRandLogStreams(
 	}
 
 	_ = g.Wait()
-	log.Printf("processed %d log streams\n", processedLogStreams.Load())
+	slog.InfoContext(ctx, "complete log stream processing", "number", processedLogStreams.Load())
 }
 
 func processLogGroup(
@@ -60,17 +60,17 @@ func processLogGroup(
 		return processed, fmt.Errorf("describe log streams: %w", err)
 	}
 	if len(allStreams) == 0 {
-		fmt.Println("no log streams found")
+		slog.InfoContext(ctx, "no log streams found")
 		return processed, nil
 	}
-	fmt.Printf("number of log streams: %d\n", len(allStreams))
+	slog.InfoContext(ctx, "list log streams", "number", len(allStreams))
 
 	randStreams := pickRandomLogStreams(allStreams, randLogStreamsNumber)
 	randStreamNames := make([]string, len(randStreams))
 	for i, s := range randStreams {
 		randStreamNames[i] = aws.ToString(s.LogStreamName)
 	}
-	fmt.Printf("randomly selected streams: %v\n", randStreamNames)
+	slog.InfoContext(ctx, "pick random log streams", "number", len(randStreamNames))
 
 	for _, srcStreamName := range randStreamNames {
 		// logGroupName/streamName/year/month/day/hour/minutes - almost the same format as CloudWatch Data Protection uses
@@ -80,8 +80,8 @@ func processLogGroup(
 			srcStreamName,
 			time.Now().UTC().Format("2006/01/02/15/04"),
 		)
-		fmt.Println("destination stream name:", dstStreamName)
 
+		slog.InfoContext(ctx, "copy log streams", "src_stream", srcStreamName, "dst_stream", dstStreamName)
 		err = cloudwatchlogs.CopyLogStream(
 			ctx,
 			client,
@@ -91,7 +91,7 @@ func processLogGroup(
 			dstStreamName,
 		)
 		if err != nil {
-			fmt.Printf("error copying log stream %s: %v\n", srcStreamName, err)
+			slog.WarnContext(ctx, "error copying log stream", "error", err)
 			continue
 		}
 		processed++

internal/sample/sample.go

@@ -3,7 +3,7 @@ package sample
 import (
 	"context"
 	"fmt"
-	"log"
+	"log/slog"
 
 	"github.com/batovpasha/aws-cw-log-sampler/internal/cloudwatchlogs"
 )
@@ -27,7 +27,7 @@ func Sample(ctx context.Context, client *cloudwatchlogs.Client, cfg *Config) err
 	if err != nil {
 		return fmt.Errorf("list log groups: %w", err)
 	}
-	log.Println("number of log groups:", len(srcGroups))
+	slog.InfoContext(ctx, "list log groups", "number", len(srcGroups))
 
 	switch cfg.Type {
 	case TypeRandLogStreams: