This project is the answer to recently missing support for Debian Strech that is basis for ruby:2.3.1
image and others. This takes Ubuntu 20.04 as base image and uses https://github.com/rbenv/ruby-build to install ruby in specific version. I will try to keep this as compatibile as possible with official ruby images.
Replace:
FROM ruby:2.3.1
With:
FROM ipepe/ubuntu-ruby:2.3.1
And it's done!
You can check available ruby versions on https://hub.docker.com/r/ipepe/ubuntu-ruby/tags. If you cannot find one there, and you really really need one, create an Issue here