This deliverable is the first of Work Package (WP) 3 related to the development of the U2Demo platform. The deliverable provides a global architecture definition and guidelines for the U2Demo platform, aiming to facilitate the development and integration of innovative peer-to-peer energy trading and sharing solutions. The document presents a high-level architecture overview, articulates critical design principles and technical specifications, and outlines essential considerations regarding security, privacy, and implementation guidelines. The ultimate objective is to establish a robust, scalable, and secure open-source foundation for subsequent project phases. This deliverable is critical for the following activities of WP3 but also for the definition of the requirements that should be considered in the development of algorithms in WP4. However, the architecture presented in this document can evolve to accommodate all the need of algorithms.