Internet of Things (IoT) faces different architectural challenges to meet the large scale application issues, the heterogeneity, and the self-adaptivity. Many IoT applications require a dynamic construction of the system and should ensure a high degree of reliability. To this end, we propose the ReDy architecture [1], which is a reusable solution for reliable and dynamic distributed IoT applications. In this paper we propose a formalization and validation of the ReDy architecture. For this end, we propose a formal model using LNT language [2]. We propose also a suitable algorithm to implement a reliable and dynamic membership management. Then we give a formal validation of this critical part based on formal modeling and model checking techniques [3].