I'd like to chime in here in support of Cloud66. I've been running normal (non-dockerized) Cloud66 for about a year on a wide variety of projects, including the main Bike Index site (https://bikeindex.org), and it's fantastic.
It's all the ease of Heroku and all the flexibility of actual servers, and way cheaper than Heroku. The only reason I've touched Docker on Cloud66 is JRuby - since this article is about a python app, it would be also require Docker. But for Ruby MRI applications, the logical first step as soon as Heroku stops being cost effective is immediate (and painless) migration to Cloud66.
It's all the ease of Heroku and all the flexibility of actual servers, and way cheaper than Heroku. The only reason I've touched Docker on Cloud66 is JRuby - since this article is about a python app, it would be also require Docker. But for Ruby MRI applications, the logical first step as soon as Heroku stops being cost effective is immediate (and painless) migration to Cloud66.