如何在Heroku上部署dockerized golang Web服务?

Please find below the logs on my heroku container:

2018-02-23T04:18:38.227618+00:00 app[web.1]: + exec app
2018-02-23T04:18:38.238070+00:00 app[web.1]: GRPC:2018/02/23 04:18:38 Starting server...
2018-02-23T04:19:35.943530+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch
2018-02-23T04:19:35.943530+00:00 heroku[web.1]: Stopping process with SIGKILL
2018-02-23T04:19:36.048633+00:00 heroku[web.1]: Process exited with status 137
2018-02-23T04:19:36.058234+00:00 heroku[web.1]: State changed from starting to crashed

I am unable to bind my app to a port. My Dockerfile specifies "EXPOSE 9090" and my go server runs on port 9090. I tried to use os.Getenv("PORT") as well but didn't have any luck.