This document summarizes the lessons learned from migrating a Ruby on Rails codebase to JRuby. Some key points covered include choosing a deployment strategy like Warbler or TorqueBox, addressing issues with forking and signals in JRuby, using thread-safe patterns to avoid sharing mutable state between threads, and alternatives to C extensions and OpenSSL in JRuby. Tuning aspects like connection pools, thread pools, and JVM memory are also discussed.