I prefer linode, aws or so.
linode : is a standard linux server. you can login, install 3rd party dependencies and play around just like in your own server. Installing nginx/rails/ruby is the same way as what you did on your own pc/laptop/server.
linode is cheap enough, $20 per month.
so, forget heroku, buy or setup your own VPS, use it for years, then you will be an linux expert.