add -json flag

.github/workflows/release.yml

@@ -12,11 +12,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Set up Go
-        uses: actions/setup-go@v4
+        uses: actions/setup-go@v5
         with:
-          go-version: "1.20"
+          go-version: "1.23"
       - name: Run GoReleaser
         uses: goreleaser/goreleaser-action@v4
         with:

.github/workflows/test.yml

@@ -5,7 +5,6 @@ jobs:
     strategy:
       matrix:
         go:
-          - "1.21"
           - "1.22"
           - "1.23"
     name: Build

.gitignore

@@ -15,4 +15,4 @@
 .envrc
 cmd/tracer/tracer
 dist/
-tracer
+./tracer

README.md

@@ -22,8 +22,14 @@ tracer [options] [cluster] [task-id]
 
   -duration duration
         fetch logs duration from created / before stopping (default 1m0s)
+  -json
+        output as JSON lines
+  -sns string
+        SNS topic ARN
+  -stdout
+        output to stdout (default true)
   -version
-    	show the version 
+        show the version
 ```
 
 Environment variable `AWS_REGION` is required.

cmd/tracer/main.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"log/slog"
 	"os"
 	"strings"
 	"time"
@@ -43,9 +44,14 @@ func main() {
 	flag.BoolVar(&showVersion, "version", false, "show the version")
 	flag.BoolVar(&opt.Stdout, "stdout", true, "output to stdout")
 	flag.StringVar(&opt.SNSTopicArn, "sns", "", "SNS topic ARN")
+	flag.BoolVar(&opt.JSON, "json", false, "output as JSON lines")
 	flag.VisitAll(envToFlag)
 	flag.Parse()
 
+	if opt.JSON {
+		slog.SetDefault(slog.New(slog.NewJSONHandler(os.Stderr, nil)))
+	}
+
 	if showVersion {
 		fmt.Println("tracer", Version)
 		return
@@ -60,7 +66,7 @@ func main() {
 	copy(args, flag.Args())
 
 	if err := t.Run(ctx, args[0], args[1], &opt); err != nil {
-		fmt.Fprintln(os.Stderr, err)
+		slog.Error(err.Error())
 		os.Exit(1)
 	}
 }

lambda.go

@@ -2,15 +2,15 @@ package tracer
 
 import (
 	"context"
-	"fmt"
+	"log/slog"
 	"strings"
 
 	"github.com/aws/aws-sdk-go-v2/aws/arn"
 )
 
 func (t *Tracer) LambdaHandlerFunc(opt *RunOption) func(ctx context.Context, event *ECSTaskEvent) error {
 	return func(ctx context.Context, event *ECSTaskEvent) error {
-		fmt.Println(event.String())
+		slog.Info("event", "payload", event.String())
 		lastStatus := event.Detail.LastStatus
 		if lastStatus != "STOPPED" {
 			return nil

lambda/function.jsonnet

@@ -2,6 +2,7 @@
   FunctionName: 'tracer',
   MemorySize: 128,
   Handler: 'index.handler',
-  Role: 'arn:aws:iam::{account_id}:role/{role_name}',
+  // Role: 'arn:aws:iam::{account_id}:role/{role_name}',
+  Role: 'arn:aws:iam::314472643515:role/tracer',
   Runtime: 'provided.al2',
 }

tracer.go

@@ -3,8 +3,10 @@ package tracer
 import (
 	"bytes"
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
+	"log/slog"
 	"os"
 	"sort"
 	"strings"
@@ -71,7 +73,7 @@ func (tl *Timeline) Add(event *TimelineEvent) {
 	tl.events = append(tl.events, event)
 }
 
-func (tl *Timeline) Print(w io.Writer) (int, error) {
+func (tl *Timeline) Print(w io.Writer, json bool) (int, error) {
 	tl.mu.Lock()
 	defer tl.mu.Unlock()
 
@@ -81,16 +83,23 @@ func (tl *Timeline) Print(w io.Writer) (int, error) {
 		return tls[i].Timestamp.Before(tls[j].Timestamp)
 	})
 	n := 0
+	toString := func(e *TimelineEvent) string {
+		if json {
+			return e.JSON()
+		}
+		return e.String()
+	}
 	for _, e := range tls {
-		s := e.String()
-		if !tl.seen[s] {
-			l, err := fmt.Fprint(w, e.String())
-			if err != nil {
-				return n, err
-			}
-			n += l
-			tl.seen[s] = true
+		s := toString(e)
+		if tl.seen[s] {
+			continue
 		}
+		l, err := fmt.Fprint(w, s)
+		if err != nil {
+			return n, err
+		}
+		n += l
+		tl.seen[s] = true
 	}
 	return n, nil
 }
@@ -106,6 +115,20 @@ func (e *TimelineEvent) String() string {
 	return fmt.Sprintf("%s\t%s\t%s\n", ts.Format(TimeFormat), e.Source, e.Message)
 }
 
+func (e *TimelineEvent) JSON() string {
+	ts := e.Timestamp.In(time.Local)
+	b, _ := json.Marshal(struct {
+		Time    string `json:"time"`
+		Source  string `json:"src"`
+		Message string `json:"msg"`
+	}{
+		Time:    ts.Format(TimeFormat),
+		Source:  e.Source,
+		Message: e.Message,
+	})
+	return string(b) + "\n"
+}
+
 func New(ctx context.Context) (*Tracer, error) {
 	region := os.Getenv("AWS_REGION")
 	awscfg, err := config.LoadDefaultConfig(ctx, config.WithRegion(region))
@@ -138,6 +161,7 @@ type RunOption struct {
 	Stdout      bool
 	SNSTopicArn string
 	Duration    time.Duration
+	JSON        bool
 }
 
 func (t *Tracer) SetOutput(w io.Writer) {
@@ -151,7 +175,7 @@ func (t *Tracer) Run(ctx context.Context, cluster string, taskID string, opt *Ru
 	defer func() { t.report(ctx, cluster, taskID) }()
 
 	if cluster == "" {
-		return t.listClusters(ctx)
+		return t.listClusters(ctx, opt)
 	}
 
 	if taskID == "" {
@@ -162,6 +186,12 @@ func (t *Tracer) Run(ctx context.Context, cluster string, taskID string, opt *Ru
 	if err != nil {
 		return err
 	}
+
+	defer func() {
+		if _, err := t.timeline.Print(t.buf, opt.JSON); err != nil {
+			slog.Error("failed to print timeline", "error", err)
+		}
+	}()
 	if err := t.traceLogs(ctx, task); err != nil {
 		return err
 	}
@@ -172,14 +202,19 @@ func (t *Tracer) Run(ctx context.Context, cluster string, taskID string, opt *Ru
 func (t *Tracer) report(ctx context.Context, cluster, taskID string) {
 	opt := t.option
 	if opt.Stdout {
-		fmt.Fprintln(t.w, subject(cluster, taskID))
+		sub := &subject{cluster, taskID}
+		if opt.JSON {
+			fmt.Fprintln(t.w, sub.JSON())
+		} else {
+			fmt.Fprintln(t.w, sub.String())
+		}
 		if _, err := t.WriteTo(t.w); err != nil {
-			fmt.Fprintln(os.Stderr, err)
+			slog.Error("failed to write to output", "error", err)
 		}
 	}
 	if opt.SNSTopicArn != "" {
 		if err := t.Publish(ctx, opt.SNSTopicArn, cluster, taskID); err != nil {
-			fmt.Fprintln(os.Stderr, err)
+			slog.Error("failed to publish to SNS", "error", err)
 		}
 	}
 }
@@ -189,19 +224,29 @@ func (t *Tracer) WriteTo(w io.Writer) (int64, error) {
 	return int64(n), err
 }
 
-func subject(cluster, taskID string) string {
-	s := "Tracer:"
-	if taskID != "" {
-		s += " " + taskID
-	} else if cluster != "" {
-		s += " tasks"
+type subject struct {
+	Cluster string `json:"cluster"`
+	TaskID  string `json:"task_id"`
+}
+
+func (s *subject) JSON() string {
+	b, _ := json.Marshal(s)
+	return string(b)
+}
+
+func (s *subject) String() string {
+	str := "Tracer:"
+	if s.TaskID != "" {
+		str += " " + s.TaskID
+	} else if s.Cluster != "" {
+		str += " tasks"
 	}
-	if cluster != "" {
-		s += " on " + cluster
+	if s.Cluster != "" {
+		str += " on " + s.Cluster
 	} else {
-		s += " clusters"
+		str += " clusters"
 	}
-	return s
+	return str
 }
 
 const (
@@ -215,7 +260,7 @@ func (t *Tracer) Publish(ctx context.Context, topicArn, cluster, taskID string)
 		msg = msg[:snsMaxPayloadSize]
 	}
 
-	s := subject(cluster, taskID)
+	s := (&subject{cluster, taskID}).String()
 	if len(s) > snsSubjectLimitLength {
 		s = s[0:snsSubjectLimitLength-len(ellipsisString)] + ellipsisString
 	}
@@ -236,7 +281,7 @@ func (t *Tracer) traceTask(ctx context.Context, cluster string, taskID string) (
 		return nil, fmt.Errorf("failed to describe tasks: %w", err)
 	}
 	if len(res.Tasks) == 0 {
-		return nil, fmt.Errorf("no tasks found: %w", err)
+		return nil, fmt.Errorf("no tasks found. cluster: %s, task_id: %s", cluster, taskID)
 	}
 	task := res.Tasks[0]
 
@@ -278,8 +323,6 @@ func (t *Tracer) traceTask(ctx context.Context, cluster string, taskID string) (
 }
 
 func (t *Tracer) traceLogs(ctx context.Context, task *ecsTypes.Task) error {
-	defer t.timeline.Print(t.buf)
-
 	res, err := t.ecs.DescribeTaskDefinition(ctx, &ecs.DescribeTaskDefinitionInput{
 		TaskDefinition: task.TaskDefinitionArn,
 	})
@@ -393,7 +436,7 @@ func (t *Tracer) listAllTasks(ctx context.Context, cluster string) error {
 	return nil
 }
 
-func (t *Tracer) listClusters(ctx context.Context) error {
+func (t *Tracer) listClusters(ctx context.Context, opt *RunOption) error {
 	res, err := t.ecs.ListClusters(ctx, &ecs.ListClustersInput{})
 	if err != nil {
 		return err
@@ -403,6 +446,17 @@ func (t *Tracer) listClusters(ctx context.Context) error {
 		clusters = append(clusters, arnToName(c))
 	}
 	sort.Strings(clusters)
+	if opt.JSON {
+		err := json.NewEncoder(t.buf).Encode(
+			struct {
+				Clusters []string `json:"clusters"`
+			}{clusters},
+		)
+		if err != nil {
+			return fmt.Errorf("failed to encode JSON: %w", err)
+		}
+		return nil
+	}
 	for _, c := range clusters {
 		t.buf.WriteString(c)
 		t.buf.WriteByte('\n')
@@ -431,9 +485,13 @@ func (t *Tracer) listTasks(ctx context.Context, cluster string, status ecsTypes.
 		if err != nil {
 			return fmt.Errorf("failed to describe tasks: %w", err)
 		}
-		for _, task := range res.Tasks {
-			t.buf.WriteString(strings.Join(taskToColumns(&task), "\t"))
-			t.buf.WriteRune('\n')
+		for _, ts := range res.Tasks {
+			task := newTask(&ts)
+			if t.option.JSON {
+				t.buf.WriteString(task.JSON())
+			} else {
+				t.buf.WriteString(task.String())
+			}
 		}
 		if nextToken = listRes.NextToken; nextToken == nil {
 			break
@@ -480,14 +538,41 @@ func arnToName(arn string) string {
 	return arn[strings.LastIndex(arn, "/")+1:]
 }
 
-func taskToColumns(task *ecsTypes.Task) []string {
-	return []string{
-		arnToName(*task.TaskArn),
-		arnToName(*task.TaskDefinitionArn),
-		aws.ToString(task.LastStatus),
-		aws.ToString(task.DesiredStatus),
-		task.CreatedAt.In(time.Local).Format(time.RFC3339),
-		aws.ToString(task.Group),
-		string(task.LaunchType),
+type task struct {
+	Arn            string `json:"arn"`
+	TaskDefinition string `json:"task_definition"`
+	LastStatus     string `json:"last_status"`
+	DesiredStatus  string `json:"desired_status"`
+	CreatedAt      string `json:"created_at"`
+	Group          string `json:"group"`
+	LaunchType     string `json:"launch_type"`
+}
+
+func newTask(t *ecsTypes.Task) *task {
+	return &task{
+		Arn:            arnToName(*t.TaskArn),
+		TaskDefinition: arnToName(*t.TaskDefinitionArn),
+		LastStatus:     aws.ToString(t.LastStatus),
+		DesiredStatus:  aws.ToString(t.DesiredStatus),
+		CreatedAt:      t.CreatedAt.In(time.Local).Format(time.RFC3339),
+		Group:          aws.ToString(t.Group),
+		LaunchType:     string(t.LaunchType),
 	}
 }
+
+func (t *task) String() string {
+	return strings.Join([]string{
+		t.Arn,
+		t.TaskDefinition,
+		t.LastStatus,
+		t.DesiredStatus,
+		t.CreatedAt,
+		t.Group,
+		t.LaunchType,
+	}, "\t") + "\n"
+}
+
+func (t *task) JSON() string {
+	b, _ := json.Marshal(t)
+	return string(b) + "\n"
+}