Why responses my heroku hosted container app with "Not authoritative" - docker

Question

I try to run my simple Web-App as Docker Container within Heroku.
When build and run the container locally all works fine.
But on accessing the generated endpoint https://html5-landingpage-buddah.herokuapp.com/ Heroku responses with HTTP 400 Bad Request and the message "Not authoritative"
Logs inside Heroku don't help much:
2020-09-19T14:45:45.269487+00:00 heroku[router]: at=info method=GET path="/" host=html5-landingpage-buddah.herokuapp.com request_id=5f07ea7e-d925-4fbe-b7ba-29387a3284cc fwd="XX.XX.XX.XXX" dyno=web.1 connect=1ms service=1ms status=400 bytes=212 protocol=https
I did a research for the error but found no helpful information.
Also re-creating the App in Heroku, renaming the URL and moving the App to another Region did not help.
Here is the log from restart to the first request on the web app:
2021-06-15T17:11:36.977277+00:00 heroku[web.1]: Starting process with command `./app`
2021-06-15T17:11:39.852345+00:00 app[web.1]: [main] INFO de.clique.westwood.example.html5.landingpage.buddah.App - Server started on port 54225
2021-06-15T17:11:39.852374+00:00 app[web.1]: [main] INFO de.clique.westwood.example.html5.landingpage.buddah.App - Serving albums from ./static/album
2021-06-15T17:11:41.363857+00:00 heroku[web.1]: State changed from starting to up
2021-06-15T17:11:48.162254+00:00 heroku[router]: at=info method=GET path="/" host=html5-landingpage-buddah.herokuapp.com request_id=85c642cb-a48d-41ac-89e1-7a520749e9bc fwd="94.31.82.142" dyno=web.1 connect=1ms service=4ms status=421 bytes=219 protocol=https
2021-06-15T17:11:48.275223+00:00 heroku[router]: at=info method=GET path="/" host=html5-landingpage-buddah.herokuapp.com request_id=406e9e77-f40e-47b9-a33b-af0af5b8f171 fwd="94.31.82.142" dyno=web.1 connect=1ms service=3ms status=421 bytes=219 protocol=https
2021-06-15T17:11:48.520876+00:00 heroku[router]: at=info method=GET path="/favicon.ico" host=html5-landingpage-buddah.herokuapp.com request_id=d3782734-765c-45f1-98a8-04e2098e7267 fwd="94.31.82.142" dyno=web.1 connect=1ms service=4ms status=421 bytes=219 protocol=https
2021-06-15T17:11:48.906097+00:00 heroku[router]: at=info method=GET path="/favicon.ico" host=html5-landingpage-buddah.herokuapp.com request_id=79e4404f-e505-4c16-9778-9f72882d74be fwd="94.31.82.142" dyno=web.1 connect=1ms service=4ms status=421 bytes=219 protocol=https

Answer 1

The error Not Authoritative simply means that Heroku is unable to redirect the traffic from the said domain name to your application.
According to Heroku,
The web process must listen for HTTP traffic on $PORT, which is set by Heroku. EXPOSE in Dockerfile is not respected, but can be used for local testing. Only HTTP requests are supported.
You will need to replace your EXPOSE and ENTRYPOINT as such
CMD [ "sh", "-c", "java -jar ./app --bind 0.0.0.0:$PORT" ]