Set Heroku Environment Variables

You’ll need to set Heroku environment variables to provide configuration
values for the config/secrets.yml file. Heroku doesn’t have a .bashrc or
.bash_profile file, so you’ll set set environment variables on Heroku
with heroku config:add.

$ heroku config:add GMAIL_USERNAME='myname@gmail.com'
GMAIL_PASSWORD='secret'
$ heroku config:add MAILCHIMP_API_KEY='mykey'
MAILCHIMP_LIST_ID='mylistid'
$ heroku config:add OWNER_EMAIL='me@example.com'
DOMAIN_NAME='myapp.herokuapp.com'

When you set myapp.herokuapp.com, replace myapp with the name that
Heroku is using for your application. If you want to use a custom domain
name, you’ll need to set up DNS (domain name service), which we won’t
cover in this tutorial.

Check that the environment variables are set with:

$ heroku config