When I tried to deploy one of my rails app on Heroku, the following problem occured.
The reason was that I set DOMAIN_NAME etc. inside secret.yml and this file was git ignored since I wanted to keep credentials private. So Heroku couldn’t find these configuration values.
Using figaro gem seems a good way to fix this. But I didn’t want to add another gem and create a new yml file.
What I did was set Heroku environment variables directly and it worked: