As it's possible that you manage the Ruby version by yourself we created the
capistrano-opscomplete Gem
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to support you with this task.
As before, add the Gem to your Gemfile:
gem 'capistrano-opscomplete', require: false
And again, actually install it by calling bundle:
$ bundle
Now make the tasks the Gem provides available to you during deploy by adding the following to your Capfile:
# Include opscomplete tasks
require 'capistrano/opscomplete'
Finally in your config/deploy.rb add the following hook which checks if the Ruby version in your .ruby-version file is already available and install it, if that's not the case:
# Install new Ruby version if not already installed
after 'deploy:updating', 'opscomplete:ruby:ensure'
If you want to handle the ruby version for rollbacks too, you should add:
after 'deploy:reverting', 'opscomplete:ruby:ensure'