Flower is a handy tool for monitoring Celery processes. As it's build on top of Tornado web server it needs it's own outside facing port and can't be run as part of your regular Heroku app which only provides one web process type. Luckily Flower is really easy to install as another app and can be run free of charge on Heroku.
This project template/guide helps you to bootstrap the process and creates a simple app for running Flower.
Clone the repo:
git clone https://github.com/jorilallo/celery-flower-heroku.git
Create an Heroku app:
heroku create APP_NAME
Configure the app by providing your broker url (RabbitMQ, Redis, what have you) and a password for logging into Flower:
heroku config:set BROKER_URL=redis://...
heroku config:set FLOWER_BASIC_AUTH="username:password"
Push to heroku:
git push heroku master
Now visit the app. It will ask for a username and a password which you defined above.