What I do is upload file to bucket, and make public link.
it work fine when I run my local nodejs host, upload succesed, make public link and able to download, however when I deploy to my nodejs hosting (Leancloud, something like Heroku) the error message was showed.

<Error>
<Code>NoSuchKey</Code>
<Message>The specified key does not exist.</Message>
</Error>

I am sure that the json file is in the root of the folder, and the "storage" is set.

var storage = gcloud.storage({
  keyFilename:  
  projectId: 
});

it works fine in local nodejs host http://localhost:3000/#/upload but not http://mywebsite/#/upload

and formidable is used to do the file handling