You will have an opportunity to create your own Heroku account during the deployment if you don't have one already.
If you want to set the software up yourself on your own hosting you will need NodeJS and MongoDB which can run on any conventional web hosting including Digital Ocean (referral link), Amazon Web Services and Microsoft Azure.
This is less necessary now that they have automated deployment from git repositories.
Create an account at Compose.io and make a database. The free one will be enough to get started.
In the "Admin" tab of your database create a new user.
In your Compose dashboard copy the "URI" from the "Admin" tab and put your user credentials in it, and then in your Heroku application:
heroku config:set playtomic=mongodb://the_uri_you_copied
Upload the application to Heroku via the command line:
git add . git commit -m "Uploading server" git push heroku master
Find your application URL via the command line:
This toolkit is designed to scale 'horizontally' by using eventual consistency, that means the more resources you assign it on Heroku the more capacity you can handle. Each 'dyno' or thread or equivalent for your hosting maintains its own caching and state that is periodically synced against your database or expired.
Heroku can be automatically scaled using HireFire.io to create and terminate 'dynos' as your load requires.
Your Compose database can be manually upgraded at any time through their website.