John Gallagher (he/him)

Based in Belfast, I’m a Principal Engineer for Dynatrace with over a decade of experience building production systems in Ruby and Rails. I'm the author of Software Design Simplified, a practical guide to better code through refactoring, TDD, and evolutionary design. Alongside by day job, I work with teams on complex systems, helping them ship safer, reduce time to recovery, and cut infrastructure costs. I’m passionate about maintainable code, developer workflows, and observability in production. Whether pairing on design problems or running workshops, I help engineers level up their understanding of how to write simpler, more resilient Ruby applications.