HYPERFLEET-908 - feat: change default log format from text to JSON

Switch the default log format to JSON for production-readiness on GKE.

- Change DefaultConfig() to use FormatJSON instead of FormatText
- Fall back to FormatJSON on unknown format in ParseLogFormat()
- Update comments to clarify FormatText is for local dev, FormatJSON for production
- Update tests to match new default behavior

Author: kuudori

pkg/logger/logger.go

@@ -37,9 +37,9 @@ const (
 type LogFormat int
 
 const (
-	// FormatText is human-readable text format (default for development)
+	// FormatText outputs logs in human-readable text format
 	FormatText LogFormat = iota
-	// FormatJSON is structured JSON format (recommended for production)
+	// FormatJSON outputs logs in JSON format for structured logging
 	FormatJSON
 )
 
@@ -102,7 +102,7 @@ func DefaultConfig() *LogConfig {
 	}
 	return &LogConfig{
 		Level:     LevelInfo,
-		Format:    FormatText,
+		Format:    FormatJSON,
 		Output:    os.Stdout,
 		Component: "sentinel",
 		Version:   "dev",
@@ -154,7 +154,7 @@ func ParseLogFormat(format string) (LogFormat, error) {
 	case "json":
 		return FormatJSON, nil
 	default:
-		return FormatText, fmt.Errorf("unknown log format: %s (valid: text, json)", format)
+		return FormatJSON, fmt.Errorf("unknown log format: %s (valid: text, json)", format)
 	}
 }
 
@@ -555,6 +555,7 @@ func (n *noopLogger) Fatal(ctx context.Context, message string) {
 	fmt.Fprintf(os.Stderr, "FATAL: %s\n", message)
 	os.Exit(1)
 }
+
 func (n *noopLogger) Fatalf(ctx context.Context, format string, args ...interface{}) {
 	fmt.Fprintf(os.Stderr, "FATAL: %s\n", fmt.Sprintf(format, args...))
 	os.Exit(1)

pkg/logger/logger_test.go

@@ -74,8 +74,8 @@ func TestParseLogFormat(t *testing.T) {
 		{"json uppercase", "JSON", FormatJSON, false},
 		{"json mixed case", "Json", FormatJSON, false},
 		{"with whitespace", "  json  ", FormatJSON, false},
-		{"invalid format", "xml", FormatText, true},
-		{"empty string", "", FormatText, true},
+		{"invalid format", "xml", FormatJSON, true},
+		{"empty string", "", FormatJSON, true},
 	}
 
 	for _, tt := range tests {
@@ -89,9 +89,9 @@ func TestParseLogFormat(t *testing.T) {
 				if err != nil {
 					t.Errorf("unexpected error for input %q: %v", tt.input, err)
 				}
-				if format != tt.expected {
-					t.Errorf("expected %v, got %v", tt.expected, format)
-				}
+			}
+			if format != tt.expected {
+				t.Errorf("expected %v, got %v", tt.expected, format)
 			}
 		})
 	}
@@ -595,8 +595,8 @@ func TestDefaultConfig(t *testing.T) {
 	if cfg.Level != LevelInfo {
 		t.Errorf("expected default level to be Info, got %v", cfg.Level)
 	}
-	if cfg.Format != FormatText {
-		t.Errorf("expected default format to be Text, got %v", cfg.Format)
+	if cfg.Format != FormatJSON {
+		t.Errorf("expected default format to be JSON, got %v", cfg.Format)
 	}
 	if cfg.Output != os.Stdout {
 		t.Error("expected default output to be stdout")
@@ -809,3 +809,16 @@ func TestLoggerErrorWithStackTrace(t *testing.T) {
 		}
 	})
 }
+
+func TestDefaultFormatIsJSON(t *testing.T) {
+	var buf bytes.Buffer
+	cfg := DefaultConfig()
+	cfg.Output = &buf
+	log := NewHyperFleetLoggerWithConfig(cfg)
+
+	log.Info(context.Background(), "test")
+
+	if !json.Valid(buf.Bytes()) {
+		t.Errorf("expected default format output to be valid JSON, got: %s", buf.String())
+	}
+}