Simple Direct File Upload to Amazon S3 in Rails


I watched the railscast episode on uploading to S3 that uses carrierwave, carrierwave_direct, fog and more gems. I was not satisfied with his solution. I wanted something simple that has the benefits of offloading the upload from the passenger process to Amazon S3. I also wanted a nice looking progress bar for upload process. In this article I discuss my simple direct File Upload to Amazon S3 using Javascript, jQuery, Amazon S3 CORS support, Simple Form with progress bar. Designed by me in Silicon Valley and developed by Denny: or

If you are looking for an elegant solution to this problem without unnecessary indirect dependencies forced by gems in Ryan Bate's solution, read on.


Step 1 - Configure S3 for CORS

  1. Create an Amazon S3 Bucket
  2. Click on Properties -> Permissions -> Edit CORS
  3. Enter a CORS configuration, such as the following. For security purposes you should restrict the origin further.
<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="">

Step 2 - Set your AWS Keys and bucket

The application can be configured via the following environment variables.


General Flow

This project uses client-side JavaScript and server-side Ruby. In general, the completed file-upload process follows these steps:

  1. A file is selected for upload by the user in their web browser.
  2. JavaScript is then responsible for making a request to your web application, which produces a temporary signature with which to sign the upload request.
  3. The temporary signed request is returned to the browser in JSON format.
  4. JavaScript then uploads the file directly to Amazon S3 using the signed request supplied by your Rails application.

Code Overview

The application flow is as follows:

  1. [Client] When the user chooses a file, a callback (defined in app/assets/javascripts/products.js) contacts the server to request a signed URL that can be used for uploading to S3.
  2. [Server] AWSController generates a signed URL according to Amazon S3 Docs and returns it using a JSON hash.
  3. [Client] The uploadToS3 function (defined in app/assets/javascripts/cors.js), takes the signed URL and the file, and PUTs the file onto S3.
  4. [Client] Once the upload is finished, the URL of the uploaded file is appended to the form as a hidden field.
  5. [Client] When the user submits the form, the file field is removed (to avoid uploading the file again). Name, price and the file URL are POSTed to the server.
  6. [Server] A new product record is created.

The most important files are are:

  • app/helpers/aws_helper - Builds the AWS authentication signature as described in Amazon S3 Docs It required the Amazon keys, as well as options about the request (request type, resource, etc).
  • app/controllers/aws_controller - Given a filename and content type, returns a JSON of the form:
  "put_url": "The *signed* URL that must be used to make the request from the client side]",
  "file_url": "The url the file will be uploaded to. A random number is appended to the file name to avoid name collisions."
  • app/assets/javascripts/cors.js - Performs the actual upload using an XMLHttpRequest. Required the signed URL, and the file to perform the request.
  • app/assets/javascripts/products.js - Handles UI callbacks, such as updating the progress bar. Also handles the file-upload callback. When the user chooses a file, the server is contacted to generate a signed URL, which is then passed to the CORS script described above to complete the upload.

Complete Source Code

The source code is available from : s3-cors-upload-rails

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