Support of Strong Consistency on Fog Applications

Providing scalability for mobile distributed applications often leads the applications to compromise their consistency requirements. However, some of these applications depend on strong consistency to guarantee that one consistent state is observed by all participants over (some of) the shared objects of the application. While deploying the application in the Cloud facilitates state management and trivially solves the strong consistency requirements, this also creates a geographical barrier between mobile devices and the application servers that penalises performance with an unavoidable latency and jitter. Fog Computing architectures can mitigate this impact by deploying surrogate servers at the network edge but its performance depends of a middleware service able to monitor the application and deploy each fragment of the state at the most convenient location. Such alternative leads to the emergence of distributed transactions that require increasing efforts to maintain strong consistency. This paper addresses how virtual synchrony, in particular a technique named Light-Weight Group (LWG), can help supporting strong consistency for mobile applications in the Fog Computing environment.