Gate k6 checks on runner being configured

This is not necessary because k6 checks won't be actually created unless
the feature flag is enabled, but to avoid issues, prevent the creation
of k6 probers unless the k6 runner is correctly configured.

Signed-off-by: Marcelo E. Magallon <marcelo.magallon@grafana.com>

cmd/synthetic-monitoring-agent/main.go

@@ -78,10 +78,6 @@ func run(args []string, stdout io.Writer) error {
 		return fmt.Errorf("invalid API token")
 	}
 
-	if err := validateK6URI(*k6URI); err != nil {
-		return fmt.Errorf("invalid k6 URI: %w", err)
-	}
-
 	baseCtx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
@@ -117,6 +113,24 @@ func run(args []string, stdout io.Writer) error {
 		Str("features", features.String()).
 		Msg("starting")
 
+	if features.IsSet(feature.K6) {
+		newUri, err := validateK6URI(*k6URI)
+		if err != nil {
+			*k6URI = ""
+			zl.Warn().Str("k6URI", *k6URI).Err(err).Msg("invalid k6 URI")
+		} else if newUri != *k6URI {
+			*k6URI = newUri
+		}
+	} else {
+		*k6URI = ""
+	}
+
+	if len(*k6URI) > 0 {
+		zl.Info().Str("k6URI", *k6URI).Msg("enabling k6 checks")
+	} else {
+		zl.Info().Msg("disabling k6 checks")
+	}
+
 	promRegisterer := prometheus.NewRegistry()
 
 	if err := registerMetrics(promRegisterer); err != nil {
@@ -172,7 +186,11 @@ func run(args []string, stdout io.Writer) error {
 	}
 	defer conn.Close()
 
-	k6Runner := k6runner.New(*k6URI)
+	var k6Runner k6runner.Runner
+
+	if features.IsSet(feature.K6) && len(*k6URI) > 0 {
+		k6Runner = k6runner.New(*k6URI)
+	}
 
 	checksUpdater, err := checks.NewUpdater(checks.UpdaterOptions{
 		Conn:           conn,
@@ -264,30 +282,28 @@ func stringFromEnv(name string, override string) string {
 	return os.Getenv(name)
 }
 
-func validateK6URI(uri string) error {
+func validateK6URI(uri string) (string, error) {
 	u, err := url.Parse(uri)
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	switch u.Scheme {
 	case "http", "https":
 
 	case "":
 		if u.Path == "" {
-			return fmt.Errorf("missing path in %q", uri)
+			return "", fmt.Errorf("missing path in %q", uri)
 		}
 
-		if false {
-			_, err := exec.LookPath(u.Path)
-			if err != nil {
-				return err
-			}
+		uri, err = exec.LookPath(u.Path)
+		if err != nil {
+			return "", err
 		}
 
 	default:
-		return fmt.Errorf("invalid scheme %q", u.Scheme)
+		return "", fmt.Errorf("invalid scheme %q", u.Scheme)
 	}
 
-	return nil
+	return uri, nil
 }

internal/prober/prober.go

@@ -70,12 +70,20 @@ func (f proberFactory) New(ctx context.Context, logger zerolog.Logger, check sm.
 		target = check.Target
 
 	case sm.CheckTypeK6:
-		p, err = k6.NewProber(ctx, check, logger, f.runner)
-		target = check.Target
+		if f.runner != nil {
+			p, err = k6.NewProber(ctx, check, logger, f.runner)
+			target = check.Target
+		} else {
+			err = fmt.Errorf("k6 checks are not enabled")
+		}
 
 	case sm.CheckTypeMultiHttp:
-		p, err = multihttp.NewProber(ctx, check, logger, f.runner)
-		target = check.Target
+		if f.runner != nil {
+			p, err = multihttp.NewProber(ctx, check, logger, f.runner)
+			target = check.Target
+		} else {
+			err = fmt.Errorf("k6 checks are not enabled")
+		}
 
 	default:
 		return nil, "", fmt.Errorf("unsupported check type")