Heroku

The default configuration won't work out of the box for Heroku, because

• Heroku doesn't allow saving files to the filesystem (although it does use tempfiles)
• We won't need Rack::Cache on Heroku because it already uses the caching proxy Varnish, which we can make use of

Instead of the normal FileDataStore, we can use the S3DataStore.

Assuming you have an S3 account set up...

Gem dependencies:

- aws-s3 (require as aws/s3)
- dragonfly

Initializer (e.g. config/initializers/dragonfly.rb):

require 'dragonfly'
app = Dragonfly[:images]

app.configure_with(:imagemagick)
app.configure_with(:rails)
app.configure_with(:heroku, 'my_bucket_name') if Rails.env.production?

app.define_macro(ActiveRecord::Base, :image_accessor)

The datastore remains as the FileDataStore for non-production environments.

environment.rb (application.rb in Rails 3):

# make sure the last arg is the same as the app's configured prefix
config.middleware.insert_before 'Rack::Lock', 'Dragonfly::Middleware', :images, '/media'

We don't store the S3 access key and secret in the repository, rather we use Heroku's config variables using the command line (we only have to do this once).

From your app's directory:

heroku config:add S3_KEY=XXXXXXXXX S3_SECRET=XXXXXXXXXX

Obviously replace 'XXXXXXXXX' with your access key and secret.

Now you can benefit from super-fast images served straight from Heroku's cache!

NOTE: HEROKU'S CACHE IS CLEARED EVERY TIME YOU DEPLOY!!!

If this is an issue, you may want to look into using something like a Memcached add-on, or maybe an after-deploy hook for hitting specific Dragonfly urls you want to cache, etc. It won't be a problem for most sites though.