When i did my ruby on rails app rollback on heroku, the application go down. How to fixed it? http://ezgo-test.herokuapp.com/
Please check logs and paste in the specific error, you can do as below.
heroku logs --tail --app app-name
As per your problem "No web processes running". you can fix it as below.
heroku ps:scale web=1 --app app-name
As per heroku documentation https://devcenter.heroku.com/articles/error-codes#h14-no-web-dynos-running .