1 - Download the RDS certificates (root plus region-specific intermediate ones) bundle:
wget -O config/rds-combined-ca-bundle.pem https://s3.amazonaws.com/rds-downloads/rds-combined-ca-bundle.pem
2 - Add config/rds-combined-ca-bundle.pem
to the repository and redeploy to Heroku.
3 - Update the DATABASE_URL
env var: