Computed Aided Engineering (CAE) allow engineers to run Computational Fluid Dynamics, Finite Element Analysis and Thermal simulations. The software is built and maintained over years with many contributors as open source in large C++ codebases. Simulation software was designed for running on a desktop client. SimScale run these in the cloud as part of a modern mircoservice architecture. Anatol Dammer on of 5 co-founders takes us behind the scenes and explains how SimScale have taken large, difficult to scale, legacy codebases and built a microservice architecture using modern programming languages.