App Platform is a Platform-as-a-Service (PaaS) offering that allows developers to publish code directly to DigitalOcean servers without worrying about the underlying infrastructure.
When you give App Platform access to your code, it defaults to using a Dockerfile if one is present in the root of the directory or specified in the app spec. Otherwise, App Platform checks your code to determine what language or framework it uses. If it supports the language or framework, it chooses an appropriate resource type and uses the proper buildpack to build the app and deploy a container.
heroku-buildpack-ruby is the buildpack for detecting and building Ruby applications.
App Platform looks for any of the following to detect a Ruby or Ruby on Rails application:
You can configure the Ruby version used at runtime by specifying a
Gemfile file at the root of your source code:
source "https://rubygems.org" ruby "2.5.1" # ...
Gemfileto an app’s repo alongside its source code.