Heroku error: No web processes running

If you ever encounter the following error in your Heroku logs, the answer is simple.

$ heroku logs

2014-05-15T08:20:31.044847+00:00 heroku[router]: at=error code=H14 desc="No web processes running" method=GET path=/favicon.ico host=your-app-name.herokuapp.com request_id=61d3dd5c-944d96-43fe-8ab5-2911042932e7 fwd="80.20.247.81" dyno= connect= service= status=503 bytes=

You probably pushed your files to Heroku and added a Procfile later to define your web dyno. Because of this Heroku does not know about that Procfile and your dyno has a size of 0.

Run this command to fix it

$ heroku ps:scale web=1