Microservices, Size Estimation, Cloud Computing, Domain-driven Design, COSMIC Function Point.

Cloud computing is becoming the de-facto standard for enterprises. The monolith applications of the past do not measure up to cloud standards. As a result, less coupled, more agile Microservices Architecture style has emerged. The Microservices Architecture proposes the use of smaller services when compared to traditional service oriented architectures. Since we were introduced to Microservices Architecture, there is an ongoing debate about what the actual size of a microservice should be. This thesis aims to identify what measures would help in finding the optimal size of a microservice. To achieve this aim, two different domain-driven design examples were taken for empirical analysis. Then those examples were modified to get more granular and less granular microservices. In the end, the more granular, original and less granular examples were compared. During the comparison, afferent coupling, efferent coupling, relational cohesion and COSMIC function points were calculated and compared. The results indicate that afferent and efferent coupling and relational cohesion values are better for deciding the optimal size. Based on the results, it is concluded that the domain-driven design can be used to obtain the optimal service granularity of microservices.