Heroku: Can app.json Provision Staging and Production Apps?

Author: Jacek Trociński, Last Revision: 2021.03.11, Topic area: Heroku

The app.json manifest file is only used when creating an application, because of this, it typically only impacts Review and CI apps, both of which are short-lived apps. Staging and production apps do not make use of the app.json file.

The app.json is specifically used with Heroku's /app-setups API endpoint. This is what Heroku uses to create Review Apps, Heroku CI apps and Button Apps. However to be clear it is only used once when the app is created. It not used after this, so if you have manually changed anything on your app after it was initially created the app.json does not get updated to align with this. It also isn't used to re-align your already existing app.