Migration and Modernization of a Loyalty Microservices System from Spring Boot 2.6 to Spring Boot 3.4

This project is part of my 6-month final year internship and involves migrating a production loyalty (fidélité) platform built with Spring Boot 2.6, Maven, REST APIs, and Swagger/OpenAPI. The system uses a microservices architecture including services like loyalty management, caisse, portail, and batch processing. My goal is to upgrade everything to Spring Boot 3.4, update dependencies, replace javax with jakarta, ensure Swagger and Spring Security compatibility, and test each service independently before full integration, and I’m mainly looking for advice on how to structure the migration phases and best practices.