Heroku is a now only a commercial service without a developer environment.
Practicalli is looking into other services as that are more developer friendly.
Using Heroku Pipelines the staging environment is promoted to production rather than being rebuilt
The Heroku dashboard can be used to promote the application into production, once the staging application is signed off.
Heroku Build processλ︎
The build process starts when commits are pushed to Heroku, either directly or via a continuous integration service (eg. CircleCI).