Upgrading GitHub to Ruby 2.7

This post details the strategy and execution of upgrading GitHub from Ruby 2.6 to Ruby 2.7. Key contributions include the dual-booting strategy using environment variables, monkey-patching the `Warning` module to collect and distribute deprecation warnings to owning teams, and the phased rollout process in production. It also highlights performance improvements such as reduced application boot time and decreased object allocations, as well as contributions back to the open-source community.