Purpose

Uploads static assets to S3 when building Heroku apps.

Requires the NodeJS buildpack to be installed. https://github.com/heroku/heroku-buildpack-nodejs

Setting Mandatory Environment Variables for Build

AWS_ACCESS_KEY_ID=<aws access key id>
AWS_SECRET_ACCESS_KEY=<aws secret access key>
AWS_DEFAULT_REGION=<aws-region>
AWS_STATIC_BUCKET_NAME=<s3-bucket-name>
# prefix to include in path
AWS_STATIC_PREFIX=static
# The directory to upload to S3 (uploads the content of the directory)
AWS_STATIC_SOURCE_DIRECTORY=public

Exported Environment Variables to Runtime

STATIC_SERVER=<AWS_STATIC_BUCKET_NAME>.s3.amazonaws.com
STATIC_PATH=/<AWS_STATIC_PREFIX>/<YYYY-MM-DD>/<git-commit-sha1>

These variables can be overriden with config vars as expected

heroku config:set STATIC_SERVER=your.cdn.host

To return to the default value just unset the config vars

heroku config:unset STATIC_SERVER