  Cloud-native Applications are 'distributed, elastic and horizontal-scalable
systems composed of (micro)services which isolate states in a minimum of
stateful components'. Hence, an important property is to ensure a low coupling
and a high cohesion among the (micro)services composing the cloud-native
application. Loosely coupled and highly cohesive services allow development
teams to work in parallel, reducing the communication overhead between teams.
However, despite both practitioners and researchers agree on the importance of
this general property, there are no validated metrics to effectively measure or
test the actual coupling level between services. In this work, we propose ways
to compute and visualize the coupling between microservices, by extending and
adapting the concepts behind the computation of the traditional structural
coupling. We validate these measures with a case study involving 17 open-source
projects and we provide an automatic approach to measure them. The results of
this study highlight how these metrics provide to practitioners a quantitative
and visual view of services compositions, which can be useful to conceive
advanced systems to monitor the evolution of the service.
