Install Ruby if not already installed

install_ruby.yml

- name: Download Ruby source
  get_url: url=https://.../ruby-{{ ruby_version }}.tar.gz dest=/tmp/ruby.tar.gz
  tags: ruby_install
  
- name: Make tmp directory for Ruby source
  file: path=/tmp/ruby state=directory
  tags: ruby_install

... Run through the rest of the configuration ...

main.yml

---
- name: Check current Ruby version
  shell: ruby --version 2>/dev/null | awk '{ print $2 }'
  register: installed_ruby_version

# {{ ruby_version }} comes from my group variables
- include_ruby.yml
  when: installed_ruby_version.stdout.find(ruby_version) != 0