Proposal: Kamal gets ruby version build arg from ruby itself

rubyonrails-core
1

Problem: The ruby version currently is duplicated at least once in a new Rails app that uses Kamal. “.ruby-version” and “Dockerfile”.

Proposal: Have the “deploy.yml.tt” generator have the following:

builder:
  ...
  args:
    RUBY_VERSION: <%= "\<%= Gem.ruby_version %>" %>

How will this solve the problem? For the default use case, Kamal is a ruby script running with the Ruby version the app uses. This means, with the above change, the builder will pass the correct Ruby version to Docker, overriding the RUBY_VERSION in the Dockerfile.

1 Like
2

The way I understand it .ruby_version is a declaration what ruby version is required for this project,

Dockerfile has it’s own mechanism to set up the world, so this requirement is fulfilled.

So I’d rather look for a way for Dockerfile to get version from .ruby_version file, than telling bundler “the required version is whatever version currently available”.

3

That is what this does. Kamal can only be run from the app directory AFAIK, which means that Gem.ruby_version is the same as the version in the file. Gem.ruby_version also handles apps that are not using .ruby_version.