Sirepo: Containerized HPC Engineering in the Cloud NaglerRobert MoellerPaul BruhwilerDavid HallChris CookNathan 2019 Sirepo is a web-application used to design particle accelerators, X-ray beamlines and other physical systems. The supported codes are written in C/C++ and FORTRAN, sometimes with Python wrappers, and rely on MPI for parallel execution. Users to date, including an increasing number of students, typically execute simulations on a single node or a small cluster. We present recent developments of the server side Sirepo, which will enable browser-based execution of these codes on a supercomputer or user-specified cluster. Containerization is the key to ensuring robust execution at all stages of Sirepo development.