heroku: procfile

https://devcenter.heroku.com/articles/procfile

Rails

web: bundle exec rails server -p $PORT

Clojure

web: lein run -m demo.web $PORT

In case you have multiple buildpacks for the application you can ensure static rendering in procfile

web: bin/boot 

See also

• Heroku, Heroku Review Apps, procfile, app.json, Heroku Flow, heroku login, heroku --help Herokudns.com, Heroku Dynos

https://elements.heroku.com/buildpacks/heroku/heroku-buildpack-static