Use download.TarballExists to make sure tarball is publicly accessible in script generator

hack/preload-images/preload_images.go

@@ -62,7 +62,7 @@ func main() {
 	for _, kv := range k8sVersions {
 		for _, cr := range containerRuntimes {
 			tf := download.TarballName(kv)
-			if tarballExists(tf) {
+			if download.PreloadExists(kv, cr) {
 				fmt.Printf("A preloaded tarball for k8s version %s already exists, skipping generation.\n", kv)
 				continue
 			}
@@ -77,13 +77,6 @@ func main() {
 	}
 }
 
-func tarballExists(tarballFilename string) bool {
-	fmt.Println("Checking if tarball already exists...")
-	gcsPath := fmt.Sprintf("gs://%s/%s", download.PreloadBucket, tarballFilename)
-	cmd := exec.Command("gsutil", "stat", gcsPath)
-	return cmd.Run() == nil
-}
-
 func verifyDockerStorage() error {
 	cmd := exec.Command("docker", "info", "-f", "{{.Info.Driver}}")
 	var stderr bytes.Buffer

hack/preload-images/upload.go

@@ -37,6 +37,13 @@ func uploadTarball(tarballFilename string) error {
 	gcsPath := fmt.Sprintf("%s/%s", gcsDest, tarballFilename)
 	cmd = exec.Command("gsutil", "acl", "ch", "-u", "AllUsers:R", gcsPath)
 	if output, err := cmd.CombinedOutput(); err != nil {
+		fmt.Printf(`Failed to update ACLs on this tarball in GCS. Please run
+		
+gsutil acl ch -u AllUsers:R %s
+
+manually to make this link public, or rerun this script to rebuild and reupload the tarball.
+		
+		`, gcsPath)
 		return errors.Wrapf(err, "uploading %s to GCS bucket: %v\n%s", hostPath, err, string(output))
 	}
 	return nil