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CarrierWave on Heroku with CloudFront

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CarrierWave on Heroku with CloudFront

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This post will enable you to have your Rails app accept file uploads through a gem called CarrierWave. Optionally, you can use CloudFront in order to have a CDN backbone for those files. This is currently the best method for file uploading on Heroku.

For a full-fledged working project with this on Heroku's cedar stack, check out http://github.com/dickeytk/painting-gallery


  • Go to S3 and get an AWS Access Key ID and an AWS Secret Access Key.
  • Create a new S3 bucket in the US East Availability Zone. (Since that's the same one that your Heroku dyno is already in)
  • If you want to use CloudFront, add a CloudFront distribution pointing to the S3 bucket you just created.


Add the gems to your Gemfile:

gem 'fog'
gem 'carrierwave'
gem 'rmagick' # optional, for image resizing support

Add the file './config/initializers/carrierwave.rb' for your CarrierWave configuration:

# ./config/initializers/carrierwave.rb
CarrierWave.configure do |config|
  config.fog_credentials = {
    :provider => "AWS",
    :aws_access_key_id => ENV['AWS_ACCESS_KEY_ID'],
    :aws_secret_access_key => ENV['AWS_SECRET_ACCESS_KEY'],
  config.fog_directory = ENV['S3_BUCKET']

  # use only one of the following 2 settings
  config.fog_host = "http://#{ENV['S3_BUCKET']}.s3.amazonaws.com" # for no cloudfront
  config.fog_host = ENV['S3_CDN'] # for cloudfront


Add your environment variables:

$ heroku config:add AWS_ACCESS_KEY_ID=[your_access_key_here]
$ heroku config:add AWS_SECRET_ACCESS_KEY=[your_access_key_here]
$ heroku config:add S3_BUCKET=[your_s3_bucket]
$ heroku config:add S3_CDN=[your_cloudfront_url] # optional for cloudfront support

That's it! Should be configured now. All you need to do is add a string column to a model for the file name, a file uploader to add files to a model, and a form to actually accept the uploads. CarrierWave's docs explain how to do that all very well.

Using your own domain

If you want to use your own domain (such as content.jeffdickey.info like I use on this site) simply add a CNAME in your dns config pointing to the S3 bucket, then change the S3_CDN environment variable to point to it.

Optional CloudFront note

Now, if you are going to use CloudFront, you should add this bit to your uploader which will append a file's hash to the end of a filename. This is so CloudFront won't cache old content.

  # ./app/uploaders/image_uploader.rb

  # ...

  # Appends hash to filename to prevent CloudFront from caching old content
  def filename
    if original_filename
      @hash ||= Digest::MD5.hexdigest(File.dirname(current_path))

Known issue

There is a potential issue to look out for here. Uploading files that will take >30 seconds will result in Heroku killing the request, so you need to directly upload the files. This S3 SWF upload plugin should help with that. But don't throw that on just 'because'. It's likely to just cause grief.


I hope this works out well for you! I've configured this type of setup several times now and seems to work great! I did it all from memory though, so let me know if you run into any issues.


Source: http://jeffdickey.info/using-carrierwave-on-heroku-for-image-uploading-w-cloudfront



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