process types
webとかworkerみたいなdynoの種別のこと webとreleaseだけ特別な処理がされる
特別なprocess type
webのみがインターネットからHTTPを受け取れる
A Heroku app’s web process type is special: it’s the only process type that can receive external HTTP traffic from Heroku’s routers. If your app includes a web server, you should declare it as your app’s web process.
releaseはRelease Phaseで使う