At GitHub, we recently added a new feature to Rails that will be available in 7.0: support for handling associations across database clusters. Read about it on the blog.
Read about GitHub’s Ruby 2.7 upgrade at https://github.blog/2020-08-25-upgrading-github-to-ruby-2-7/.
Read about GitHub’s Rails 6.0 upgrade at https://github.blog/2019-09-09-running-github-on-rails-6-0/.
Read about GitHub’s Rails upgrade at https://github.blog/2018-09-28-upgrading-github-from-rails-3-2-to-5-2/.