Using spec to Transparently Replace a Legacy System

Daniel Solano Gómez 
Outpace Systems, Inc.

Replacing a legacy production system can be a harrowing task, especially if you are not 100% sure about how it works. What if you had a tool that can help you understand how that legacy system behaves and ensures the replacement works the same way? As we discovered, we have such a tool: Clojure’s spec library. Through a combination of parsing logs and exercising the legacy system, we gained the understanding to ensure that the replacement retained many of the quirks of the old one. The end result was a complete success: we were able to replace the system with zero downtime and no surprises.

Daniel is a developer at Outpace Systems and a long-time member of the Clojure community. He has contributed to Clojure and maintains several open source projects, such as neko, tacular, liberator-transit, and leinjacker. Additionally, Daniel is a member of the Clojars Community Committee and a long-time participant in Clojure’s Google Summer of Code efforts. He recently joined up with Packt to produce ‘Mastering Clojure programming’, a video series aimed at Clojure beginners who want to transition to writing larger, practical programs.