Vaiheittaisen modernisointistrategian suunnittelu perintökoodiin perustuvalle logistiikkajärjestelmälle

Legacy logistics systems often accumulate technical debt over a long lifetime, which can make maintenance and making changes painful and risky. As these systems are commonly business critical systems, replacement or a big bang rewrite is often not possible or a good business decision, due to operational and organizational constraints. This thesis investigates incremental modernization as an alternative strategy for a legacy logistics system of a Finnish company. The thesis uses a constructive research approach to combine system analysis, literature review and construction of usable artifacts. The study identified three main sources of debt and problems: architectural, process and knowledge debt. As a result, the study constructed and designed an iterative modernization strategy utilizing strangler fig pattern, modular monolith as a target architecture, and modernized development processes as the artifacts. The strategy and the technical solutions were demonstrated as feasible through a proof-of-concept implementation focusing on modernizing a CO2 emissions reporting module. The implementation showed that the modernized components of the new modular monolith can coexist with the legacy system and be taken into use with strategic and controlled routing. The results show that the suggested modernization strategy provides a concrete starting point for the incremental modernization of the mission critical legacy system.